Impact of SumiLarv® 2MR on Aedes aegypti larvae: a multicenter study in Brazil

BACKGROUND

Aedes aegypti is associated with dengue, Zika, and chikungunya transmission. These arboviruses are responsible for national outbreaks with severe public health implications. Vector control is one of the tools used to prevent mosquito proliferation, and SumiLarv® 2MR is an alternative commercial product based on pyriproxyfen for larval/pupal control. In this study, the residual effectiveness of SumiLarv® 2MR in different regions of Brazil was evaluated in simulated field conditions.

METHODS

We conducted a multicenter study across four Brazilian states-Amapá, Pernambuco, Rio de Janeiro, and São Paulo-given the importance to the country's climatic variances in the north, northeast, and southeast regions and their influence on product efficiency. The populations of Ae. aegypti from each location were held in an insectary. Third-instar larvae (L3) were added every 2 weeks to water containers with SumiLarv® 2MR discs in 250-, 500- and 1000-l containers in Amapá and Rio de Janeiro, and 100-l containers in Pernambuco and São Paulo, using concentrations of 0.04, 0.08, and 0.16 mg/l.

RESULTS

Adult emergence inhibition over 420 days was observed in all tests conducted at a concentration of 0.16 mg/l; inhibition for 308-420 days was observed for 0.08 mg/l, and 224-420 days for 0.04 mg/l.

CONCLUSIONS

Sumilarv® 2MR residual activity demonstrated in this study suggests that this new pyriproxyfen formulation is a promising alternative for Aedes control, regardless of climatic variations and ideal concentration, since the SumiLarv® 2MR showed adult emergence inhibition of over 80% and residual activity greater than 6 months, a period longer than that recommended by the Ministry of Health of Brazil between product re-application in larval breeding sites.

Regionality in vector control: effect of fluctuating temperature in the susceptibility of Aedes aegypti (Diptera: Culicidae) larvae to Pyriproxyfen

Using Pyriproxyfen in controlling Aedes aegypti shows great potential considering its high competence in low dosages. As an endocrine disruptor, temperature can interfere with its efficiency, related to a decrease in larval emergence inhibition in hotter environments. However, previous studies have been performed at constant temperatures in the laboratory, which may not precisely reflect the environmental conditions in the field. The aim of this study was to assess the effect of the fluctuating temperatures in Pyriproxyfen efficiency on controlling Aedes aegypti larvae. We selected maximum and minimum temperatures from the Brazilian Meteorological Institute database from September to April for cities grouped by five regions. Five fluctuating temperatures (17-26; 20-28.5; 23-32.5; 23-30.5; 19.5-31 °C) were applied to bioassays assessing Pyriproxyfen efficiency in preventing adult emergence in Aedes aegypti larvae in five concentrations. In the lowest temperatures, the most diluted Pyriproxyfen treatment (0.0025 mg/L) was efficient in preventing the emergence of almost thrice the larvae than in the hottest temperatures (61% and 21%, respectively, p value = 0.00015). The concentration that inhibits the emergence of 50% of the population was lower than that preconized by the World Health Organization (0.01 mg/L) in all treatments, except for the hottest temperatures, for which we estimated 0.010 mg/L. We concluded that fluctuating temperatures in laboratory bioassays can provide a more realistic result to integrate the strategies in vector surveillance. For a country with continental proportions such as Brazil, considering regionalities is crucial to the rational use of insecticides.

Community perception of the autodissemination of pyriproxyfen for controlling malaria vectors in south-eastern Tanzania

BACKGROUND

The efficacy of the autodissemination of pyriproxyfen to control malaria vectors has been demonstrated under semi field environment in Tanzania. However, the information on how best communities should be engaged for its routine and large-scale adoption are lacking. This study assessed the community's level of knowledge, perceptions, acceptability of the autodissemination of pyriproxyfen, and the perceived risks on the safety of pyriproxyfen on the environment.

METHODS

This was a concurrent mixed methods study, comprised of a community-based survey of 400 household representatives and eight focus group discussions (FGDs). The study was conducted in two villages in Mlimba district in south-eastern Tanzania between June and August 2022. For the quantitative data analysis, descriptive statistics were applied using R software, while inductive approach was used for qualitative data analysis, using NVivo software.

RESULTS

Knowledge on autodissemination of pyriproxyfen approach was found to be relatively low among both the FGD respondents and surveyed community members (36%, n = 144). Nevertheless, when it was explained to them, the envisioned community support for the autodissemination approach was relatively high (97%, n = 388). One of the major perceived benefits of the autodissemination of pyriproxyfen was the reduction of malaria-transmitting mosquitoes and associated malaria transmission. Environmental impact of pyriproxyfen on non-target organisms and health risk to children were among the major concerns. When provided with information on the safety and its utilization particularly through autodissemination approach, 93.5% (n = 374) of the survey respondents said that they would allow the PPF-contaminated pots to be placed around their homes. Similarly, FGD respondents were receptive towards the autodissemination of pyriproxyfen, but emphasized on the need for raising awareness among community members before related field trials.

CONCLUSION

This study indicates a low knowledge but high support for scaling up of the autodissemination of pyriproxyfen as a complementary tool for malaria control in rural Tanzania. The Findings of this study suggest that community sensitization activities are required to improve the community's acceptability and trust of the approach before respective field trials.

In vitro screening of genotoxicity and mutagenicity of pyriproxyfen in human lymphocytes and Salmonella typhimurium TA98 and TA100 strains

Pyriproxyfen (PPX) is a pesticide/larvicide used to increase productivity in agriculture against insects by inhibiting development of insects' larvae. In this study, cytotoxic, genotoxic, and mutagenic effects of PPX were investigated in human peripheral lymphocytes and Salmonella typhimurium strains by performing chromosomal aberration, micronucleus (MN) tests, and Ames test, respectively. For the chromosome aberration (CA) and MN methods, blood from four healthy donors (two men and two women, nonsmokers) were used. Two hundred microliters of blood was inoculated into PbMax medium and prepared according to International Guidelines. For the Ames test, S. typhimurium TA98 and TA100 strains were used to detect frameshift and base pair substitution mutagens, respectively. PPX induced both the CA percentage and MN frequency in human peripheral lymphocytes and exhibited cytotoxic effects. In addition, it showed a mutagenic effect at all doses in TA98 and TA100 strains in the presence of S9mix; however, no such effect was observed in the absence of S9mix. According to the obtained results, it can be said that PPX has genotoxic and mutagenic potentials.

The promoting effects of pyriproxyfen on autophagy and apoptosis in silk glands of non-target insect silkworm, Bombyx mori

Pyriproxyfen is a juvenile hormone analogue. The physiological effects of its low-concentration drift during the process of controlling agricultural and forestry pests on non-target organisms in the ecological environment are unpredictable, especially the effects on organs that play a key role in biological function are worthy of attention. The silk gland is an important organ for silk-secreting insects. Herein, we studied the effects of trace pyriproxyfen on autophagy and apoptosis of the silk gland in the lepidopteran model insect, Bombyx mori (silkworm). After treating fifth instar silkworm larvae with pyriproxyfen for 24 h, we found significant shrinkage, vacuolization, and fragmentation in the posterior silk gland (PSG). In addition, the results of autophagy-related genes of ATG8 and TUNEL assay also demonstrated that autophagy and apoptosis in the PSG of the silkworm was induced by pyriproxyfen. RNA-Seq results showed that pyriproxyfen treatment resulted in the activation of juvenile hormone signaling pathway genes and inhibition of 20-hydroxyecdysone (20E) signaling pathway genes. Among the 1808 significantly differentially expressed genes, 796 were upregulated and 1012 were downregulated. Among them, 30 genes were identified for autophagy-related signaling pathways, such as NOD-like receptor signaling pathway and mTOR signaling pathway, and 30 genes were identified for apoptosis-related signaling pathways, such as P53 signaling pathway and TNF signaling pathway. Further qRT-PCR and in vitro gland culture studies showed that the autophagy-related genes Atg5, Atg6, Atg12, Atg16 and the apoptosis-related genes Aif, Dronc, Dredd, and Caspase1 were responsive to the treatment of pyriproxyfen, with transcription levels up-regulated from 24 to 72 h. In addition, ATG5, ATG6, and Dronc genes had a more direct response to pyriproxyfen treatment. These results suggested that pyriproxyfen treatment could disrupt the hormone regulation in silkworms, promoting autophagy and apoptosis in the PSG. This study provides more evidence for the research on the damage of juvenile hormone analogues to non-target organisms or organs in the environment, and provides reference information for the scientific and rational use of juvenile hormone pesticides.

Current and future opportunities of autodissemination of pyriproxyfen approach for malaria vector control in urban and rural Africa

Despite the progress made in reducing malaria burden, new ways to address the increasing challenges of insecticide resistance and the invasion and spread of exotic malaria vectors such as Anopheles stephensi in Africa are urgently needed. While African countries are adopting larviciding as a complementary intervention for malaria vector control, the autodissemination technology has the potential to overcome barriers associated with the identification and treatment of prolific habitats that impede conventional larviciding approaches in rural settings. The autodissemination technology as a "lure and release" strategy works by exploiting the resting behavior of gravid mosquitoes to transfer lethal concentration of biological or chemical insecticide such as pyriproxyfen (PPF), an insect growth regulator (IGRs) to their oviposition sites and result in adult emergence inhibition. Despite the evidence of the autodissemination approach to control other mosquito-borne diseases, there is growing and promising evidence for its use in controlling malaria vectors in Africa, which highlights the momentous research that needs to be sustained. This article reviews the evidence for efficacy of the autodissemination approach using PPF and discusses its potential as efficient and affordable complementary malaria vector control intervention in Africa. In the previous studies that were done in controlled semi-field environments, autodissemination with PPF demonstrated its potential in reducing densities of captive population of malaria vectors such as Anopheles gambiae and Anopheles arabiensis. Of importance, empirical evidence and biology-informed mathematical models to demonstrate the utility of the autodissemination approach to control wild populations of malaria vectors under field environment either alone or in combination with other tools are underway. Among others, the key determining factors for future introduction of this approach at scale is having scalable autodissemination devices, optimized PPF formulations, assess its integration/complementarity to existing conventional larviciding, and community perception and acceptance of the autodissemination approach.

Sterilized Anopheles funestus can autodisseminate sufficient pyriproxyfen to the breeding habitat under semi-field settings

BACKGROUND

Anopheles funestus, the main malaria vector, prefer to oviposit in permanent and/or semi-permanent breeding habitats located far from human dwellings. Difficulties in identifying and accessing these habitats jeopardize the feasibility of conventional larviciding. In this way, a semi-field study was conducted to assess the potential of autodissemination of pyriproxyfen (PPF) by An. funestus for its control.

METHODS

The study was conducted inside a semi-field system (SFS). Therein, two identical separate chambers, the treatment chamber with a PPF-treated clay pot (0.25 g AI), and the control chamber with an untreated clay pot. In both chambers, one artificial breeding habitat made of a plastic basin with one litre of water was provided. Three hundred blood-fed female An. funestus aged 5-9 days were held inside untreated and treated clay pots for 30 min and 48 h before being released for oviposition. The impact of PPF on adult emergence, fecundity, and fertility through autodissemination and sterilization effects were assessed by comparing the treatment with its appropriate control group.

RESULTS

Mean (95% CI) percentage of adult emergence was 15.5% (14.9-16.1%) and 70.3% (69-71%) in the PPF and control chamber for females exposed for 30 min (p < 0.001); and 19% (12-28%) and 95% (88-98%) in the PPF and control chamber for females exposed for 48 h (p < 0.001) respectively. Eggs laid by exposed mosquitoes and their hatch rate were significantly reduced compared to unexposed mosquitoes (p < 0.001). Approximately, 90% of females exposed for 48 h retained abnormal ovarian follicles and only 42% in females exposed for 30 min.

CONCLUSION

The study demonstrated sterilization and adult emergence inhibition via autodissemination of PPF by An. funestus. Also, it offers proof that sterilized An. funestus can transfer PPF to prevent adult emergence at breeding habitats. These findings warrant further assessment of the autodissemination of PPF in controlling wild population of An. funestus, and highlights its potential for complementing long-lasting insecticidal nets.

Evaluating the attrition, fabric integrity and insecticidal durability of two dual active ingredient nets (Interceptor® G2 and Royal® Guard): methodology for a prospective study embedded in a cluster randomized controlled trial in Benin

BACKGROUND

Following the World Health Organization (WHO) endorsement of dual active ingredient (AI) nets, an increased uptake of pyrethroid-chlorfenapyr and pyrethroid-pyriproxyfen nets is expected. Studies evaluating their physical and insecticidal durability are essential for making programmatic and procurement decisions. This paper describes the methodology for a prospective study to evaluate the attrition, fabric integrity, insecticidal durability of Interceptor® G2 (alpha-cypermethrin-chlorfenapyr) and Royal Guard® (alpha-cypermethrin-pyriproxyfen), compared to Interceptor® (alpha-cypermethrin), embedded in a 3-arm cluster randomized controlled trial (cRCT) in the Zou Department of Benin.

METHODS

Ten clusters randomly selected from each arm of the cRCT will be used for the study. A total of 750 ITNs per type will be followed in 5 study clusters per arm to assess ITN attrition and fabric integrity at 6-, 12-, 24- and 36-months post distribution, using standard WHO procedures. A second cohort of 1800 nets per type will be withdrawn every 6 months from all 10 clusters per arm and assessed for chemical content and biological activity in laboratory bioassays at each time point. Alpha-cypermethrin bioefficacy in Interceptor® and Royal Guard® will be monitored in WHO cone bioassays and tunnel tests using the susceptible Anopheles gambiae Kisumu strain. The bioefficacy of the non-pyrethroid insecticides (chlorfenapyr in Interceptor® G2 and pyriproxyfen in Royal Guard®) will be monitored using the pyrethroid-resistant Anopheles coluzzii Akron strain. Chlorfenapyr activity will be assessed in tunnel tests while pyriproxyfen activity will be assessed in cone bioassays in terms of the reduction in fertility of blood-fed survivors observed by dissecting mosquito ovaries. Nets withdrawn at 12, 24 and 36 months will be tested in experimental hut trials within the cRCT study area against wild free-flying pyrethroid resistant An. gambiae sensu lato to investigate their superiority to Interceptor® and to compare them to ITNs washed 20 times for experimental hut evaluation studies. Mechanistic models will also be used to investigate whether entomological outcomes with each dual ITN type in experimental hut trials can predict their epidemiological performance in the cRCT.

CONCLUSION

This study will provide information on the durability of two dual AI nets (Interceptor® G2 and Royal Guard®) in Benin and will help identify suitable methods for monitoring the durability of their insecticidal activity under operational conditions. The modelling component will determine the capacity of experimental hut trials to predict the epidemiological performance of dual AI nets across their lifespan.

Assessing the susceptibility and efficacy of traditional neurotoxic (pyrethroid) and new-generation insecticides (chlorfenapyr, clothianidin, and pyriproxyfen), on wild pyrethroid-resistant populations of Anopheles gambiae from southern Benin

BACKGROUND

The objective of this study was to determine the susceptibility of wild Anopheles gambiae sensu lato (s.l.) from southern Benin to the new insecticides (chlorfenapyr (CFP), pyriproxyfen (PPF), and clothianidin (CTD)) and assess the efficacy of insecticide-treated bed nets (ITNs) that contain these new products.

METHODS

Wild An. gambiae from the Benin communes of Allada, Ifangni, Akpro-Missérété, and Porto-Novo were tested for their susceptibility to CFP and PPF using the WHO bottle tests, and pyrethroids (alpha-cypermethrin, deltamethrin, and permethrin) and CTD using WHO tube tests. WHO cone tests were used to evaluate the efficacy of Interceptor® (which contains alpha-cypermethrin (ACM) only), Interceptor® G2, (CFP + ACM), and Royal Guard® nets (PPF + ACM). The ovaries of blood-fed An. gambiae from Ifangni exposed to a new PPF net were dissected, and egg development status was examined using Christopher's stages to determine the fertility status of the mosquitoes. Using a standardized protocol, the oviposition rate and oviposition inhibition rate were calculated from live blood-fed An. gambiae placed in oviposition chambers after exposure to PPF.

RESULTS

In all four mosquito populations, pyrethroid mortality ranged from 5 to 80%, while chlorfenapyr and clothianidin mortality ranged from 98 to 100%. At Ifangni, all mosquitoes exposed to Royal Guard® nets were infertile (100%) while the majority (74.9%) of mosquitoes exposed to Interceptor® nets had fully developed their eggs to Christopher's stage V. The oviposition inhibition rate after exposure of the mosquitoes to the PPF was 99% for the wild population of An. gambiae s.l. and the susceptible laboratory strain, An. gambiae sensu stricto (Kisumu).

CONCLUSIONS

The results of this study suggest that pyrethroid-resistant An. gambiae from the selected communes in southern Benin are susceptible to chlorfenapyr, clothianidin, and pyriproxyfen. In addition, based on bioassay results, new and unused Interceptor® G2 and Royal Guard® nets were effective on Ifangni's mosquito populations. Despite the availability of new effective insecticides, continued vigilance is needed in Benin. Therefore, monitoring of resistance to these insecticides will continue to periodically update the Benin national insecticide resistance database and management plan.

Pyriproxyfen influences growth as well as thyroid hormone-related and gh/igf-1 gene expression during the early life stage of zebrafish (Danio rerio)

Pyriproxyfen is an agricultural chemical pesticide that has been detected in the aquatic environment. This study aimed to clarify the effects of pyriproxyfen on the growth as well as thyroid hormone- and growth-related gene expression of zebrafish (Danio rerio) during its early life stage. Pyriproxyfen exhibited a lethal effect in a concentration-dependent manner: the lowest and no effect concentrations were 250.7 and 111.7 μg/L, respectively. These concentrations were considerably higher than the residual environmental concentrations, indicating the low risk of this pesticide when present at such concentrations. In the zebrafish group treated with 56.6 μg/L pyriproxyfen, thyroid hormone receptor β gene expression levels remained unchanged, whereas thyroid-stimulating hormone β subunit, iodtyronin deiodinase 2, and thyroid hormone receptor α gene expression levels significantly decreased compared with the control group expression levels. In zebrafish treated with 111.7 or 250.7 μg/L pyriproxyfen, iodtyronin deiodinase 1 gene expression levels significantly increased. These results indicate that pyriproxyfen disrupts thyroid hormone activity in zebrafish. Furthermore, pyriproxyfen exposure inhibited zebrafish growth; consequently, we examined the expression of growth hormone (gh) and insulin-like growth factor-I (igf-1), which are important for growth. Pyriproxyfen exposure suppressed gh expression; however, the igf-1 expression levels remained unchanged. Therefore, growth inhibition due to pyriproxyfen exposure was attributed to the suppression of gh expression.

Molecularly imprinted ormosil as a sorbent for targeted dispersive solid phase micro extraction of pyriproxyfen from strawberry samples

Novel molecularly imprinted organically modified silica was prepared by reacting acrylamide and 3-(tri-methoxysilyl) propyl methacrylate followed by condensation and hydrolysis with tetraethyl ortho-silicate for the determination of pyriproxyfen. The sorbent proved to be highly selective for the template molecule, pyriproxyfen. The characterization of sorbent was carried out using SEM, BET and TGA. The prominent peaks in FTIR at 3700 cm^-1 and 1071 cm^-1 confirmed the stretching of amide group's N-H and Si-O-Si bond linkage of MI_Ormosil. The pseudo-first-order model (R² 0.99) described the adsorption kinetics of the MI_Ormosil, whereas among adsorption isotherms, Freundlich model showed the best fit (R² 0.99). The molecularly imprinted silica was applied for the determination of target analytes from strawberries sample using dispersive solid-phase micro extraction (DSPME) followed by high-performance liquid chromatography (HPLC). The LOD (4.93 x10^-5 μg mL^-1) and LOQ (1.49 x10^-4 μg m-¹) values were calculated by signal to noise ratio through HPLC. Results show that the maximum binding capacity and percentage recovery values of MI_Ormosil were 13 mg g^-1 (n = 5) and 97.3% respectively.

The inhibition of ecdysone signal pathway was the key of pyriproxyfen poisoning for silkworm, Bombyx mori

Pyriproxyfen is a juvenile hormone-like pesticide. Once intake occurs, it leads to a series of poisoning characters consequences in silkworm, Bombyx mori (ID: 7091, Lepidoptera), such as non- cocooning, non-pupation, production of low-active eggs, and extended stages. However, the poisoning mechanism is still unclear. Here, silkworms were fed mulberry leaves soaked with different pyriproxyfen concentrations, and the heads were dissected for transcriptome analysis, while the hemolymph was used for determinations of ecdysone and juvenile hormone titers. As a result, after conjoint analysis of 3 feeding groups and a control group, 555 differentially expressed genes (DEGs) were obtained, which were mainly involved in hormone metabolism, glycometabolism and protein metabolism. Meanwhile, 119 genes were significantly correlated with the pyriproxyfen concentrations, and they were mainly involved in drug metabolism and glycometabolism. The ecdysone titers in several feeding groups were significantly lower than those of the control group, while juvenile hormone was not detected in all groups, including the control and feeding groups. Correspondingly, due to activation of the juvenile hormone signaling pathway by pyriproxyfen, key genes in the ecdysone synthesis pathway were downregulated, and a large number of downstream genes were up- or downregulated. In addition, nearly all genes in the detoxification pathway were upregulated. These results suggested that, affected by the juvenile hormone signaling pathway, ecdysone titers decreased and further affected a series of downstream processes, and this was the key reason for pyriproxyfen poisoning in silkworm, B. mori, which could lay a foundation for the study of pyriproxyfen resistance in silkworm.

Fate and dietary risk assessment of pyriproxyfen, dinotefuran, and its metabolites residues in tomato across different regions in China

Registration of a new formulation called 30% suspension concentrate (30% SC, pyriproxyfen 10% + dinotefuran 20%) to inhibit the occurrence of whitefly in tomato is currently under review in China, so it is necessary to research the residue behavior and dietary risk of pyriproxyfen and dinotefuran in tomato under field conditions. According to Good Agricultural Practices (GAP), the formulation was sprayed once at the dosage of 112.5 g a.i./ha (active ingredient/hectare) at the initial stage of the occurrence of tomato whitefly and the recommended pre-harvest interval (PHI) for sampling was 5 days. Meanwhile, the residues of pyriproxyfen, dinotefuran, and the metabolites of dinotefuran in tomato samples were determined using QuEChERS (quick, easy, cheap, effective, rugged, and safe) and high-performance liquid chromatography-tandem mass spectrometry. The results showed that the terminal residue levels of the analytes detected in tomato samples were below 0.19 mg/kg for pyriproxyfen and 0.25 mg/kg for dinotefuran at the recommended PHI (5 days), which were lower than the maximum residue limits of China. The dietary risk assessment was also carried out based on field trial results, toxicological data, and Chinese dietary pattern. Both the chronic risk quotients (≤ 26.59%) and acute risk quotients (≤ 1.14%, general population, > 1 year) of pyriproxyfen and dinotefuran were far below 100%, indicating a low risk to consumers' health. The paper will be conducive to provide guidance for the rational application of these insecticides on tomato.

Toxicological effects of trace amounts of pyriproxyfen on the midgut of non-target insect silkworm

Pyriproxyfen is an insect growth regulator that is widely used in public health and pest control in agriculture. Our previous studies have shown that trace amounts of pyriproxyfen in the environment can cause serious toxic effects in the non-target insect silkworm, including failing to pupate, metamorphose and spin cocoons. However, it is unknown why pyriproxyfen not only has no lethal effects on fifth instar larvae but also tend to increase their body weight. The midgut is the main digestive organs of the silkworm, our results showed that the residual of pyriproxyfen in the silkworm at 24 h after 1 × 10^-4 mg/L pyriproxyfen treatment caused severe damage to the midgut microvilli, goblet cells, and nuclei of the silkworm, but body weight and digestibility of the larval were both increased. In addition, pyriproxyfen significantly (p < 0.05) increased the activities of digestive enzymes (α-amylase, trehalase, trypsin and lipase) in the midgut of silkworm. However, it caused down-regulation of ecdysone synthesis-related genes at the end of the fifth instar silkworm, decreased ecdysone titer, and prolonged larval instar. At the same time, pyriproxyfen also activated transcription of detoxification enzymes-related genes such as the cytochrome P450 enzyme genes Cyp9a22 and Cyp15C1, the carboxylesterase genes CarE-8 and CarE-11, and the glutathione S-transferase gene GSTo2. This study elucidated a novel toxicological effect of pyriproxyfen to insects, which not only expands the understanding of the effects of juvenile hormone pesticides on lepidopteran insects but also provides a reference for exploring the ecological security of non-target organisms.

Persistence, leaching and associated toxicity risks of insecticide pyriproxyfen in soil ecosystem

Pyriproxyfen is a pyridine-based insecticide used for pest control in fruits and vegetables. It is a potent endocrine disruptor and hormone imitator. Considering its potential hazards to non-target organisms and the associated environment, a lab study was conducted for assessing persistence, mobility in sandy loam soil and associated risk to various non-target organisms and soil enzymes. Pyriproxyfen formulation was applied at 0.05 and 0.10 µg g^-1 soil which was equivalent to recommended and double dose of 100 and 200 g a.i. ha^-1, respectively. Three methods namely QuEChERS, liquid-solid extraction (LSE) and matrix solid phase dispersion (MSPD) were compared for achieving efficient sample preparation. MSPD was applied for final analysis as it gave better recoveries (94.2 to 104.3%) over other methods with limits of detection and quantification (LOD and LOQ) as 0.0001 and 0.0005 µg g^-1, respectively. Dissipation followed first order kinetics with half-lives of 7.6 and 8.2 days in both doses but residues retained over 45 days in soil. Leaching studies conducted at 50 and 100 µg of pyriproxyfen showed extremely poor leaching potential. Retention of over 90% residues in top 5 cm soil surface indicated minimal threat of ground and surface water contamination. Toxicological study demonstrated very different behaviour toward different enzymatic activities. Pyriproxyfen was relatively toxic for alkaline phosphatase and fluorescein diacetate hydrolase enzymes. β-glucosidase activity was triggered whereas arylsulfatase activity remained unaffected. Unacceptable risk to soil invertebrates at double dose application clearly indicated that its longer persistence in soil could be toxic to other non-target organisms and needs further investigations.

Novel pyriproxyfen based treatment for Aedes breeding control through a long-lasting formulation: Laboratory and field trials in Western Maharashtra, India

BACKGROUND & OBJECTIVES

There is a need to evaluate novel techniques for dengue control in India. Several formulations of pyriproxyfen have been assessed for efficacy and duration of action. Pyriproxyfen is also used as a microencapsulated ready-to-use formulation against the Aedes vector. We evaluated a novel pyriproxyfen-based microencapsulated formulation. This slow-release, ready-to-use aqueous spray is a larvicidal formulation, and we assessed its efficacy and residual action through laboratory and semi-field trials against Aedes immature stages.

METHODS

The study was carried out as per the guidelines for laboratory and field/small-scale field testing of mosquito larvicides by the World Health Organization. The evaluation was conducted in laboratory and semi-field conditions from August to December 2018. We tested the novel formulation on three materials (plastic, ceramic, and enamel) in the laboratory for its action as an antilarval. Four containers of each kind were sprayed with the formulation and kept as replicates. Four controls were used in the laboratory trials - 120 larvae (third instar) were introduced in the replicates and the controls each. Readings were taken daily till complete adult emergence or larval and pupal mortality. In the semi-field trials, we applied this formulation to the inside of desert coolers and observed larvicidal and pupicidal activity over five months. Data is presented in numbers and percentages, along with mean and standard deviation. Adult emergence and Emergence Inhibition was calculated.

RESULTS

There was 100% adult emergence inhibition amongst the exposed larvae in the treated containers in the laboratory trials. In the untreated controls, adult emergence ranged from 80-95% in all types of containers. In the semifield trials, Inhibition Emergence was 100% in the treated desert coolers during the five months of the study period.

INTERPRETATION & CONCLUSION

This advancement in insecticide formulation technology promises to make dengue control more effective and efficient.

Restricted double access mesoporous polypyrrole as adsorbent in pipette-tip solid phase extraction for simultaneous determination of progesterone, pyriproxyfen, and deltamethrin in chicken eggs

In this study, two sample preparation techniques were evaluated in the simultaneous determination of three compounds with different physicochemical properties, progesterone, pyriproxyfen, and deltamethrin that may be present in the chicken egg. In this procedure, firstly the restricted double access mesoporous polypyrrole was synthesized, which was evaluated as adsorbent in pipette-tip solid phase extraction and dispersive solid phase extraction. After optimizing the extraction parameters, it was found that pipette-tip solid phase extraction was more efficient and, therefore, it was used in the validation and application of the method. The analytical method showed good recoveries, acceptable linearity (r > 0.99), limits of quantification, precision and accuracy, robustness and stability within the limits of the literature. Finally, the developed method was successfully applied in simultaneous determination of analytes in different chicken egg samples. Therefore, this work provided a promising strategy for the extraction of different organic compounds from egg products.

Behavior of two classes of organic contaminants in the presence of graphene oxide: Ecotoxicity, physicochemical characterization and theoretical calculations

Graphene oxide (GO) production has increased considerably and therefore its presence in the environment is inevitable. When in aquatic environment GO can interact with co-existing compounds, modifying their toxicities for several organisms. However, the toxic effects of co-exposure of GO and organic compounds are rarely reported in the literature. Herein, we studied the behavior of four organic aquatic contaminants found in surface water such as 2-phenylbenzotriazoles (non-Cl PBTA-9 and PBTA-9) and phenoxyphenyl pesticides, pyriproxyfen (PYR) and lambdacyhalothrin (LCT), in the presence of GO. GO reduced 90% and 83% of the toxicity of non-Cl PBTA-9 and PBTA for Daphnia. When PBTAs were adsorbed onto GO surface their interactions caused GO agglomeration (up to 20 mm) and consequent precipitation, making PBTAs less bioavailable. PYR and LCT's toxicities increased up to 83% for PYR and 47% for LCT in the presence of GO, because their adsorption on GO lead to the stabilization of the suspensions (up to 0.5 μm). Those particles were then easily ingested and retained in the digestive tract of the daphnids, triggering the Trojan horse effect. Based on theoretical calculations we observed that PBTA compounds are planar, electron-poorer and more reactive than the studied pesticides, suggesting a better stability of the GO/PBTA complexes. PYR and LCT are nonplanar, electron-richer and less reactive towards GO than PBTAs, forming less stable GO complexes that could facilitate the desorption of pesticides, increasing toxic effects. Our results suggest that the properties of the organic toxicants can influence the stability of graphene oxide suspensions, playing a fundamental role in the modulation of their toxicity. Further research is needed for a deep understanding of the behavior of nanomaterials in the presence of contaminants and their effect in the toxicity of aquatic organisms.

Durability of three types of dual active ingredient long-lasting insecticidal net compared to a pyrethroid-only LLIN in Tanzania: methodology for a prospective cohort study nested in a cluster randomized controlled trial

BACKGROUND

Progress achieved by long-lasting insecticidal nets (LLINs) against malaria is threatened by widespread selection of pyrethroid resistance among vector populations. LLINs with non-pyrethroid insecticides are urgently needed. This study aims to assess the insecticide and textile durability of three classes of dual-active ingredient (A.I.) LLINs using techniques derived from established WHO LLIN testing methods to set new standards of evaluation.

METHODS

A WHO Phase 3 active ingredients and textile durability study will be carried out within a cluster randomized controlled trial in 40 clusters in Misungwi district, Tanzania. The following treatments will be evaluated: (1) Interceptor®G2 combining chlorfenapyr and the pyrethroid alpha-cypermethrin, (2) Royal Guard® treated with pyriproxyfen and alpha-cypermethrin, (3) Olyset™ Plus which incorporates a synergist piperonyl butoxide and the pyrethroid permethrin, and (4) a reference standard alpha-cypermethrin only LLIN (Interceptor®). 750 nets will be followed in 5 clusters per intervention arm at 6, 12, 24 and 36 months post distribution for survivorship and hole index assessment. A second cohort of 1950 nets per net type will be identified in 10 clusters, of which 30 LLINs will be withdrawn for bio-efficacy and chemical analysis every 6 months up to 36 months and another 30 collected for experimental hut trials every year. Bio-efficacy will be assessed using cone bioassays and tunnel tests against susceptible and resistant laboratory strains of Anopheles gambiae sensu stricto. Efficacy of field-collected nets will be compared in six experimental huts. The main outcomes will be Anopheles mortality up to 72 h post exposure, blood feeding and egg maturation using ovary dissection to assess impact on fecundity.

CONCLUSIONS

Study findings will help develop bio-efficacy and physical durability criteria for partner A.I., in relation to the cRCT epidemiological and entomological outcomes, and refine preferred product characteristics of each class of LLIN. If suitable, the bioassay and hut outcomes will be fitted to transmission models to estimate correlation with cRCT outcomes.

TRIAL REGISTRATION NUMBER

NCT03554616.

LC-MS/MS method for the simultaneous quantification of pyriproxyfen and bifenthrin and their dissipation kinetics under field conditions in chili and brinjal

Bifenthrin, a synthetic pyrethroid, and pyriproxyfen, a plant growth regulator, are used extensively in agriculture for controlling the different insect pests. The present study was undertaken to examine the dissipation behavior of a formulation with a combination of pyriproxyfen and bifenthrin on chili and brinjal under field conditions at four different locations. Dissipation study of combination of pyriproxyfen and bifenthrin revealed swift degradation in both crops with a half-life of 2.5-2.6 and 2.0-2.1 days in brinjal and chili, respectively. Also, a simple method for simultaneous quantification of pyriproxyfen and bifenthrin was developed and validated using modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) technique on liquid chromatography with tandem mass spectrometry (LC-MS/MS). Recovery of the method was found to be under an acceptable range of 90.0%-93.5% and 88.7%-94.3% in chili and 92.4%-96.6% and 97.4%-100.9% in brinjal for pyriproxyfen and bifenthrin, respectively. At harvest time, the terminal residues of bifenthrin and pyriproxyfen were below the maximum residue limits set by European Union in chili and brinjal, respectively, suggesting that the use of this pesticide formulation is safe and does not impose harmful effects on human health. PRACTICAL APPLICATION: In this paper, dissipation behavior of a pesticide formulation with a combination of pyriproxyfen and bifenthrin was undertaken under field conditions at four different locations on chili and brinjal in India. The simultaneous quantification of pyriproxyfen and bifenthrin using LC-MS/MS technique has been validated incorporating modified QuEChERS extraction method with limit of detection at 0.005 µg/g and limit of quantification at 0.01 µg/g, which is well below the EU-MRLs (European Union legislation Maximum Residue Level) of pyriproxyfen and bifenthrin in both chili and brinjal. Furthermore, dissipation kinetics of a formulation undertaken under field conditions at four different locations on chili and brinjal suggested that the terminal residues of both bifenthrin and pyriproxyfen were below the maximum residue limits set by European Union in chili and brinjal, respectively, at the time of harvest and that the use of this pesticide formulation is safe.

The JH-Met2-Kr-h1 pathway is involved in pyriproxyfen-induced defects of metamorphosis and silk protein synthesis in silkworms, Bombyx mori

Environmental residues of pryriproxyfen, a juvenile hormone analogue (JHA) type pesticide, may have on unintended consequences on non-target insects. However, the mechanism of pyriproxyfen action and silk protein synthesis in silkworms has not been reported. In the present study, we treated the silkworms with trace pyriproxyfen (1 × 10^-4 mg/L) and found that the silkworm larvae showed no obvious poisoning symptoms, while the development of silk glands and cocoon-forming function were both seriously damaged due to the accumulation of pyriproxyfen in posterior silk gland (PSG). The titer of the juvenile hormone (JH) was increased, whereas the content of 20-hydroxyecdysone (20E) was reduced in pyriproxyfen-exposed hemolymph. Met2 is a component of the JH receptor complex and JH can promote its phosphorylation. We found Met2 and SRC were up-regulated in the larval stage after pyriproxyfen exposure, the JH-Met2/SRC complex led to the up-regulation of downstream genes Kr-h1, and Dimm, and then specifically inhibited the transcription of Fib-H. Meanwhile, the transcription of ecdysone inducible transcription factor Br-C Z4 was also inhibited by pyriproxyfen and resulted in the defects of metamorphosis. In conclusion, the trace pyriproxyfen could affect the metamorphosis and silk protein synthesis through the Met2-mediated pathway. Our study provided new evidence that Met2 might be a potential target gene of JHA in Lepidoptera.

The pyriproxyfen metabolite, 4'-OH-PPF, disrupts thyroid hormone signaling in neural stem cells, modifying neurodevelopmental genes affected by ZIKA virus infection

North-Eastern Brazil saw intensive application of the insecticide pyriproxyfen (PPF) during the microcephaly outbreak caused by the Zika virus (ZIKV). ZIKV requires the neural RNA-binding protein Musashi-1 to replicate. Thyroid hormone (TH) represses MSI1. PPF is a suspected TH disruptor. We hypothesized that co-exposure to the main metabolite of PPF, 4'-OH-PPF, could exacerbate ZIKV effects through increased MSI1 expression. Exposing an in vivo reporter model, Xenopus laevis, to 4'-OH-PPF decreased TH signaling and increased msi1 mRNA and protein, confirming TH-antagonistic properties. Next, we investigated the metabolite's effects on mouse subventricular zone-derived neural stem cells (NSCs). Exposure to 4'-OH-PPF dose-dependently reduced neuroprogenitor proliferation and dysregulated genes implicated in neurogliogenesis. The highest dose induced Msi1 mRNA and protein, increasing cell apoptosis and the ratio of neurons to glial cells. Given these effects of the metabolite alone, we considered if combined infection with ZIKV worsened neurogenic events. Only at the fourth and last day of incubation did co-exposure of 4'-OH-PPF and ZIKV decrease viral replication, but viral RNA copies stayed within the same order of magnitude. Intracellular RNA content of NSCs was decreased in the combined presence of 4'-OH-PPF and ZIKV, suggesting a synergistic block of transcriptional machinery. Seven out of 12 tested key genes in TH signaling and neuroglial commitment were dysregulated by co-exposure, of which four were unaltered when exposed to 4'-OH-PPF alone. We conclude that 4'-OH-PPF is an active TH-antagonist, altering NSC processes known to underlie correct cortical development. A combination of the TH-disrupting metabolite and ZIKV could aggravate the microcephaly phenotype.

Quantitative determination of pyriproxyfen and its metabolite residues in bee products of China using a modified QuEChERS approach with UPLC-MS/MS

Given the key role of bees as indicators for environmental assessment, residues in bees and bee products have attracted great interest. In this regard, an improved, highly sensitive method for quantifying the insecticide pyriproxyfen and its four metabolites (4'-OH-Pyr, DPH-Pyr, 2-OH-PY, 4'-OH-POP) in honeybees, larvae, and bee products (honey, pollen, royal jelly and wax) should be established. For this purpose, we used ultra-performance liquid chromatography coupled with triple-quadrupole mass spectrometry for rapid quantification (≤5 min). Recoveries for various matrices ranged from 73.77% to 114.97%, with satisfactory intra-day and inter-day precision (relative standard deviations of 0.03-8.61% and 0.10-7.25%, respectively). The results demonstrated excellent linearity (R² > 0.9903) with a limit of quantification of 1 μg/kg for six different matrices. We collected and analyzed 597 samples (honey, bees and wax) from four major beekeeping areas in China. Only 47 of these samples contained residues of pyriproxyfen and two of its metabolites (2-OH-PY, 4'-OH-Pyr), and high levels of contamination were found in bee samples (2-739 μg/kg), with substantive accumulation in wax (levels were 9.49% higher than in other samples). The result demonstrate that the method provides a reliable and convenient means of monitoring pyriproxyfen and its metabolites in bee products for better product quality, human health, and international commercial competition and also lays a foundation for risk assessment of potential pyriproxyfen contamination in China.

Toxicity and fate of chiral insecticide pyriproxyfen and its metabolites in zebrafish (Danio rerio)

Pyriproxyfen is a juvenile hormone analogue insecticide used worldwide. At present, the potential threat of pyriproxyfen to aquatic organism has not been well explored. In this work, the bioaccumulation, metabolic profile and toxicity of pyriproxyfen and its metabolites to zebrafish were studied, and the enantioselectivity of pyriproxyfen and the major chiral metabolites were also determined. Sixteen metabolites of pyriproxyfen in zebrafish were identified. Hydroxylation, ether linkage cleavage and oxidation in phase I metabolism, followed by sulfate and glucuronic acid conjugation. The bioconcentration factors ranged from 1175 to 1246. Hydroxylation metabolites of pyriproxyfen showed enantioselective behavior in zebrafish with enantiomer fractions (EFs) of 4'-OH- pyriproxyfen and 5″-OH- pyriproxyfen ranged from 0.50 to 0.71. Toxicological indexes including acute toxicity, joint toxicity and oxidative stress were tested. Among all the metabolites, 4'-OH- pyriproxyfen was found 2 folds more toxic to zebrafish than pyriproxyfen. (-)-Pyriproxyfen was found 2 folds more toxic than rac- and (+)-pyriproxyfen. Antagonistic effects were found in binary joint toxicity of pyriproxyfen and its hydroxylated metabolites. Pyriproxyfen and its metabolites also showed oxidative stress damage by inhibiting the activity of CAT and SOD and increasing MDA. This work provided deep insight into the metabolism and the potential risks of pyriproxyfen to aquatic organisms.

Pyriproxyfen induces intracellular calcium overload and alters antioxidant defenses in Danio rerio testis that may influence ongoing spermatogenesis

We investigated the in vitro effects of pyriproxyfen on ionic balance in the testis of the zebrafish by measuring ⁴⁵Ca²⁺ influx. In vivo pyriproxyfen treatment was carried out to study oxidative stress, and conduct morphological analysis of the testis and liver. Whole testes were incubated in vitro with/without pyriproxyfen (10^-12, 10^-9 or 10^-6 M; 30 min) and ⁴⁵Ca²⁺ influx determined. To study pyriproxyfen's mechanism of action, inhibitors/activators of ionic channels or pumps/exchangers, protein kinase inhibitors or a calcium chelator were added 15 min before the addition of ⁴⁵Ca²⁺ and pyriproxyfen. We evaluated the in vivo effects of 7 day exposure to waterborne pyriproxyfen (10^-9 M) on reactive oxygen species (ROS) formation, lipid peroxidation, and reduced glutathione content (GSH), glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT) and γ-glutamyltransferase (GGT) activity. Morphological analyses of the testis and liver were carried out after in vivo exposure of D. rerio to pyriproxyfen. Pyriproxyfen increased ⁴⁵Ca²⁺ influx by opening the voltage-dependent T-type channels (T-type VDCC), inhibiting sarco/endoplasmic reticulum ⁴⁵Ca²⁺-ATPase (SERCA) and the NCX exchanger (forward mode) and by mobilizing calcium from stores. The involvement of potassium channels and protein kinase C (PKC) was also demonstrated in pyriproxyfen-induced intracellular calcium elevation. In vivo pyriproxyfen treatment of D. rerio increased lipid peroxidation, decreased GSH content and increased GST activity in testes, in addition to increasing the number and size of spermatogonia cysts and inducing hepatocyte basophilia and dilation of blood vessels in the liver. The toxicity of pyriproxyfen is mediated by calcium overload, increased lipid peroxidation, and a diminished antioxidant capacity in the testis, due to GSH depletion, and altered spermatogenesis. The development of high basophilia in the liver suggests that pyriproxyfen may have estrogenic activity, possibly acting as an endocrine-disruptor. These findings indicate that these alterations may contribute to pyriproxyfen toxicity and spermatogenesis disruption.

in rural Tanzania

Fundamentally, larviciding with pyriproxyfen (PPF) has potential to complement Long Lasting Insecticide Nets (LLINs) and indoor residual sprays (IRS) in settings where resistance to pyrethroids and residual malaria transmission exist. In this study, we evaluated the field effectiveness of larviciding using PPF to reduce dry season productivity of mosquito breeding habitats that were located by pastoralists within the study area. Using pastoralist knowledge, dry season breeding habitats in Mofu village rural Tanzania were located and monitored for larval productivity for a period of 8 months before PPF intervention. During the intervention, six out of twelve breeding habitats were treated with Sumilarv 0.5G PPF granules. The impact of deposited PPF was monitored by recording emergence inhibition of larvae collected from treated habitats compared to the appropriate control group for a period of three months and half post-intervention. During baseline, the average proportion (+SD) of adult emerged was similar between two clusters, with (0.89 + 0.22) for the control cluster and (0.93 + 0.16) for the treatment cluster of breeding habitats. Following treatment with PPF, the average proportion (+SD) of adult emerged in the treated breeding habitats was significantly low (0.096 + 0.22) compared to adults that emerged from larvae in the untreated habitats (0.99 + 0.22) (p < 0.0001). Of all emerged adults, approximately 94% were An. gambiae s.l. and the remaining 6% were An. funestus s.l. This is the first study demonstrating the usefulness of engaging pastoralist community to locate and identify hard to find mosquito breeding habitats. Reduced productivity of the targeted habitats with PPF offers prospect of implementing PPF larviciding in dry season when habitats are few and permanent to control mosquito population in rural settings.

Effect of pyriproxyfen exposure on cocooning and gene expression in the silk gland of Bombyx mori （Linnaeus, 1758）

Bombyx mori（Linnaeus, 1758） is an important economical insect, and the sericulture is a flourishing industry in many developing countries. Pyriproxyfen, a juvenile hormone pesticide, is often applied to cultivations widely in the world, and its exposure often resulted in silk yield reduction and non-cocooning. However, the effect of pyriproxyfen exposure on cocooning and gene expression level in the silk gland of B. mori has not been studied yet, and this study focused on the above issues. The result indicated that pyriproxyfen exposure can lead to silk gland injury, reduction of silk yield and cocooning rate. Furthermore, the expression levels of silk protein synthesis related genes were down regulated significantly. The same change trends were shown between PI3K/Akt and CncC/Keap1 pathway, which is the expressions of key genes can be elevated by pyriproxyfen exposure. In addition, the activity of detoxification enzymes (P450, GST and CarE) and the expression levels of detoxification genes were elevated after pyriproxyfen exposure, suggesting that detoxification enzymes may play an important role in detoxification of pyriproxyfen in silk gland. These results provided possible clues to the silk gland injury and gene transcriptional level changes in silkworm after pyriproxyfen exposure.

Sublethal effects of a juvenile hormone analog, Pyriproxyfen on demographic parameters of non-target predator, Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae)

Insect predators, in general, play an important role in regulating pest populations in agricultural systems, but may be negatively affected by pesticides used in pest management. Convergent lady beetle, Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae) is known as an important biological control agent of soft-bodied insect pests. The development of Integrated Pest Management (IPM) program against insect pests requires an assessment of the side effect of insecticides on biological control agents. In the present work, we assessed the sublethal effects of an insect growth regulator, Pyriproxyfen (juvenile hormone mimic) on a common aphidophagous beetle, H. convergens by computing its demographic parameters through age-stage, two-sex life table theory. Present results showed that sublethal (LC₁₀ and LC₃₀) concentrations of tested insecticide prolonged the pre-adult developmental duration while adult longevity, fecundity and fertility were reduced following treatment compared with control. However, total pre-ovipositional period (TPOP) was declined with the increasing trend of insecticide concentration. In additions, population growth parameters such as intrinsic rate of increase r, finite rate of increase λ and net reproductive rate R₀ were dramatically reduced in H. convergens population when they treated with sublethal concentrations pyriproxyfen. Therefore, the results obtained through this study reflected that pyriproxyfen impairs the population growth parameters and could reduce the biological services provided by H. convergens. Thus, more attention should be paid to the use of this insecticide in IPM program.

Effects of pyriproxyfen exposure on immune signaling pathway and transcription of detoxification enzyme genes in fat body of silkworm, Bombyx mori

Sericulture is a very important and flourishing industry in developing countries. Bombyx mori is a kind of important and well-studied economic insects in the whole world. In China, applying of pyriproxyfen pesticide often resulted in non-cocooning and silk yield reduction. However, the effects of pyriproxyfen exposure on immune signaling pathway in fat body of silkworm has not been reported yet now. In the present study, we found that the growth and development of silkworm were significantly affected by pyriproxyfen exposure and the fat body tissues were injured after treatment. It was also showed that the expressions of key genes of PI3K/Akt and CncC/Keap1 pathway can be elevated at 24-96 h after pyriproxyfen exposure. Furtherly, the relative expression levels of detoxification enzyme genes and the activities of detoxification enzymes were both increased by pyriproxyfen exposure. These results provided comprehensive view of fat body injury and gene expression changes in silkworm after pyriproxyfen exposure.

Measuring mosquito control: adult-mosquito catches vs egg-trap data as endpoints of a cluster-randomized controlled trial of mosquito-disseminated pyriproxyfen

BACKGROUND

Aedes aegypti and Culex quinquefasciatus are the main urban vectors of arthropod-borne viruses causing human disease, including dengue, Zika, or West Nile. Although key to disease prevention, urban-mosquito control has met only limited success. Alternative vector-control tactics are therefore being developed and tested, often using entomological endpoints to measure impact. Here, we test one promising alternative and assess how three such endpoints perform at measuring its effects.

METHODS

We conducted a 16-month, two-arm, cluster-randomized controlled trial (CRCT) of mosquito-disseminated pyriproxyfen (MD-PPF) in central-western Brazil. We used three entomological endpoints: adult-mosquito density as directly measured by active aspiration of adult mosquitoes, and egg-trap-based indices of female Aedes presence (proportion of positive egg-traps) and possibly abundance (number of eggs per egg-trap). Using generalized linear mixed models, we estimated MD-PPF effects on these endpoints while accounting for the non-independence of repeated observations and for intervention-unrelated sources of spatial-temporal variation.

RESULTS

On average, MD-PPF reduced adult-mosquito density by 66.3% (95% confidence interval, 95% CI: 47.3-78.4%); Cx. quinquefasciatus density fell by 55.5% (95% CI: 21.1-74.8%), and Ae. aegypti density by 60.0% (95% CI: 28.7-77.5%). In contrast, MD-PPF had no measurable effect on either Aedes egg counts or egg-trap positivity, both of which decreased somewhat in the intervention cluster but also in the control cluster. Egg-trap data, therefore, failed to reflect the 60.0% mean reduction of adult Aedes density associated with MD-PPF deployment.

CONCLUSIONS

Our results suggest that the widely used egg-trap-based monitoring may poorly measure the impact of Aedes control; even if more costly, direct monitoring of the adult mosquito population is likely to provide a much more realistic and informative picture of intervention effects. In our CRCT, MD-PPF reduced adult-mosquito density by 66.3% in a medium-sized, spatially non-isolated, tropical urban neighborhood. Broader-scale trials will be necessary to measure MD-PPF impact on arboviral-disease transmission.

Impact of pyriproxyfen on virus behavior: implications for pesticide-induced virulence and mechanism of transmission

Background

More than 3 years since the last Zika virus (ZIKV) outbreak in Brazil, researchers are still deciphering the molecular mechanisms of neurovirulence and vertical transmission, as well as the best way to control spread of ZIKV, a flavivirus. The use of pesticides was the main strategy of mosquito control during the last ZIKV outbreak.

Methods

We used vesicular stomatitis virus (VSV) tagged with green fluorescent protein (GFP) as our prototypical virus to study the impact of insecticide pyriproxyfen (PPF). VZV-GFP infected and uninfected Jurkat, HeLa and trophoblast cells were treated with PPF and compared to untreated cells (control). Cell viability was determined by the MTT assay. Cell morphology, presence of extracellular vesicles (EVs), virus infection/GFP expression as well as active mitochondrial levels/localization were examined by confocal microscopy.

Results

PPF, which was used to control mosquito populations in Brazil prior to the ZIKV outbreak, enhances VSV replication and has cell membrane-altering properties in the presence of virus. PPF causes enhanced viral replication and formation of large EVs, loaded with virus as well as mitochondria. Treatment of trophoblasts or HeLa cells with increasing concentrations of PPF does not alter cell viability, however, it proportionately increases Jurkat cell viability. Increasing concentrations of PPF followed by VSV infection does not interfere with HeLa cell viability. Both Jurkats and trophoblasts show proportionately increased cell death with increased concentrations of PPF in the presence of virus.

Conclusions

We hypothesize that PPF disrupts the lipid microenvironment of mammalian cells, thereby interfering with pathways of viral replication. PPF lowers viability of trophoblasts and Jurkats in the presence of VSV, implying that the combination renders immune system impairment in infected individuals as well as enhanced vulnerability of fetuses towards viral vertical transmission. We hypothesize that similar viruses such as ZIKV may be vertically transmitted via EV-to-cell contact when exposed to PPF, thereby bypassing immune detection. The impact of pesticides on viral replication must be fully investigated before large scale use in future outbreaks of mosquito borne viruses.

Repeated exposure of pyriproxyfen to pregnant female mice causes developmental abnormalities in prenatal pups

The continuous exposure to conventional pesticides leads to severe health and environmental issues especially at prenatal stage during developmental period. Herein, we aimed to investigate the anomalies due to repeated exposure of pyriproxyfen in pregnant female mice and their neonates. Twenty-four pregnant female mice were repeatedly administered with pyriproxyfen at 30, 100, 300, and 1000 mg/kg by oral gauge from gestation day (GD) 7 to gestation day 17 and six females were given distilled water in the control group. All the live pups were euthanized at postnatal day (PND) 7 and their organs (heart, liver, kidney, and brain) were dissected out, weighed, and assessed for further histopathological examinations. The results exhibited a significant (P < 0.001) decrease in the body weight gain of all treated pregnant mice in comparison to the controls and a significant increase in the gestational length was observed in group IV (P < 0.01) and group V (P < 0.001). In addition, no live pups were born in groups IV and V and one pregnant female mouse was also found dead in both treatments. The body weights of the pups were significantly decreased in group II (P < 0.05) and group III (P < 0.001) and the relative organ (liver, heart, and kidney) weight of the pups was increased significantly (P < 0.001, P < 0.01, P < 0.05) due to prenatal exposure in group II as compared to group I. The relative brain weights of the pups were decreased significantly (P < 0.001) in groups II and III as compared to group I. The liver, kidney, heart, and brain sections exhibited various histological alterations in groups II and III by hematoxylin and eosin staining. Furthermore, immunohistochemical staining of the coronal sections of pup's brain showed significant (P < 0.001) reduction in cortical radial thickness and total neural count in group II and III as compared to group I. Therefore, the prenatal exposure to pyriproxyfen provoked the damage to various organs in mice offspring and an increase in fetal death at higher doses.

Aedes mosquito surveillance and the use of a larvicide for vector control in a rural area of the Lao People's Democratic Republic

Background

Refillable water containers are commonly used in rural areas of Lao PDR, and they act as Aedes mosquito breeding sites. Aedes aegypti and Ae. albopictus mosquitos are transmission vectors for the dengue virus, which causes dengue fever.

Methods

Two isolated rural villages in the central part of Lao PDR were selected as study sites. In the intervention village, domestic water containers were continuously treated with a long-lasting matrix release formulation, containing pyriproxyfen, named SumiLarv®2MR. In the control village, entomological activity was monitored, but no intervention was performed. Baseline data were collected in both villages during the late rainy season (October 2017) then distributed SumiLarv®2MR disks in intervention village. This data was compared with data collected during the intervention periods in the dry season (February 2018), rainy season (July 2018 and 2019), and late rainy season (September 2018) in the region.

Results

Compared with the baseline data (20.24%), the percentage of water containers infested with Ae. aegypti larvae was significantly decreased in the treated village, especially in the rainy seasons in July 2018 (4.11%; P < 0.001) and July 2019 (2.46%; P < 0.001), while the percentage of water containers infested with Ae. albopictus larvae did not decrease significantly in prevalence. No reduction in the frequency of Aedes species was seen in the control village. The Ae. albopictus liked to breed in small habitats (the median water volume of its habitats was 5 L and 10 L in the control and treated village, respectively, while the equivalent values for Ae. aegypti were 30 L and 50 L, respectively).

Conclusion

The treatment of refillable water storage containers in a rural village with SumiLarv®2MR disks led to significant reductions in the Ae. aegypti population. However, the Ae. albopictus population did not decrease in either the control or treated village. This discrepancy was due to differences in habitat-seeking behaviors and preferred breeding sites such as types of water, water container, and water volume, then led to the differences in results of mosquito prevalence after SumiLarv®2MR disk treatments. The SumiLarv®2MR disk treatment was proven to be effective against the primary dengue-virus vector mosquitoes, Ae. aegypti.

The comparative metabolic response of Bactrocera dorsalis larvae to azadirachtin, pyriproxyfen and tebufenozide

Azadirachtin, as the most promising and effective botanical insecticide, exhibits significant growth inhibition activity against agricultural and forestry pests. However, its biochemical effects at the metabolic level compared with those of other insect growth regulators have not been studied. Therefore, in this study, a GC-MS based untargeted metabolomics approach was applied to compare azadirachtin with pyriproxyfen (a juvenile hormone analog) and tebufenozide (a molting hormone analog) in terms of their metabolic effects on Bactrocera dorsalis larvae. The bioactivity of azadirachtin against B. dorsalis larvae was significantly different than those of pyriproxyfen and tebufenozide. A total of 693 mass features were recognized, and 112 metabolites were identified in this study. The results showed that a total of 16, 13 and 10 differentially regulated metabolites corresponding to 12, 5 and 8 pathways occur in Aza versus CK, Pyr versus CK and Teb versus CK group, respectively. Further analysis showed that 6 differentially regulated metabolites corresponding to 5 key pathways could be the primary differential metabolic response of B. dorsalis larvae to the three insect growth regulators. The pathways were myo-inositol corresponding to ascorbate and aldarate metabolism as the specific response of B. dorsalis larvae to azadirachtin; xylitol, xylulose and 3-aminopropionitrile corresponding to pentose and glucuronate interconversions, and cyanoamino acid metabolism as the common responses to azadirachtin and pyriproxyfen; and 3-hydroxypropionic acid and beta-alanine corresponding to propanoate metabolism and beta-alanine metabolism as the specific responses to tebufenozide. The results showed that the metabolic response of B. dorsalis larvae to azadirachitin is closer to that of pyriproxyfen than tebufenozide. The differentially regulated metabolites and pathways responsible for this difference are discussed.

Assessing the impact of the addition of pyriproxyfen on the durability of permethrin-treated bed nets in Burkina Faso: a compound-randomized controlled trial

BACKGROUND

Long-lasting insecticidal nets (LLINs) treated with pyrethroids are the foundation of malaria control in sub-Saharan Africa. Rising pyrethroid resistance in vectors, however, has driven the development of alternative net formulations. Here the durability of polyethylene nets with a novel combination of a pyrethroid, permethrin, and the insect juvenile hormone mimic, pyriproxyfen (PPF), compared to a standard permethrin LLIN, was assessed in rural Burkina Faso.

METHODS

A compound-randomized controlled trial was completed in two villages. In one village 326 of the PPF-permethrin nets (Olyset Duo) and 327 standard LLINs (Olyset) were distributed to assess bioefficacy. In a second village, 170 PPF-permethrin nets and 376 LLINs were distributed to assess survivorship. Nets were followed at 6-monthly intervals for 3 years. Bioefficacy was assessed by exposing permethrin-susceptible and resistant Anopheles gambiae sensu lato mosquito strains to standard World Health Organization (WHO) cone and tunnel tests with impacts on fertility measured in the resistant strain. Insecticide content was measured using high-performance liquid chromatography. LLIN survivorship was recorded with a questionnaire and assessed by comparing the physical integrity using the proportionate hole index (pHI).

RESULTS

The PPF-permethrin net met WHO bioefficacy criteria (≥ 80% mortality or ≥ 95% knockdown) for the first 18 months, compared to 6 months for the standard LLIN. Mean mosquito mortality for PPF-permethrin nets, across all time points, was 8.6% (CI 2.6-14.6%) higher than the standard LLIN. Fertility rates were reduced after PPF-permethrin net exposure at 1-month post distribution, but not later. Permethrin content of both types of nets remained within the target range of 20 g/kg ± 25% for 242/248 nets tested. The pyriproxyfen content of PPF-permethrin nets declined by 54%, from 10.4 g/kg (CI 10.2-10.6) to 4.7 g/kg (CI 3.5-6.0, p < 0.001) over 36 months. Net survivorship was poor, with only 13% of PPF-permethrin nets and 12% of LLINs still present in the original household after 36 months. There was no difference in the fabric integrity or survivorship between the two net types.

CONCLUSION

The PPF-permethrin net, Olyset Duo, met or exceeded the performance of the WHO-recommended standard LLIN (Olyset) in the current study but both net types failed the 3-year WHO bioefficacy criteria.

Testing a pyriproxyfen auto-dissemination station attractive to gravid Anopheles gambiae sensu stricto for the development of a novel attract-release -and-kill strategy for malaria vector control

BACKGROUND

Larviciding is an effective supplementary tool for malaria vector control, but the identification and accessibility of aquatic habitats impedes application. Dissemination of the insect growth regulator, pyriproxyfen (PPF), by gravid Anopheles might constitute a novel application strategy. This study aimed to explore the feasibility of using an attractive bait-station to contaminate gravid Anopheles gambiae sensu stricto with PPF and subsequently transfer PPF to larval habitats.

METHODS

A bait-station was developed comprising of an artificial pond containing water treated with 20 ppm cedrol, an oviposition attractant, and a netting-cover treated with PPF. Three identical semi-field cages were used to assess the potential of gravid Anopheles to transfer PPF from the bait-station to ponds. Gravid females were released in two semi-field cages, one with PPF on its bait-station (test) and one without PPF (control). No mosquitoes were released in the third cage with a PPF-treated station (control). Transfer of PPF to open ponds was assessed by monitoring emergence of late instar insectary-reared larvae introduced into the ponds. The amount of PPF carried by a mosquito and transferred to water was quantified using liquid chromatography-mass spectrometry.

RESULTS

In the controls, 86% (95% CI 81-89%) of larvae introduced into open ponds developed into adults, indicating that wind did not distribute PPF in absence of mosquitoes. Emergence inhibition was observed in the test cage but was dependent on the distance between pond and bait-station. Only 25% (95% CI 22-29%) of larvae emerged as adults from ponds 4 m from the bait-station, but 92% (95% CI 89-94%) emerged from ponds 10 m away. Each mosquito was contaminated on average with 112 μg (95% CI 93-123 μg) PPF resulting in the transfer of 230 ng/L (95% CI 180-290 ng/L) PPF to 100 ml volumes of water.

CONCLUSIONS

The bait-stations successfully attracted gravid females which were subsequently dusted with effective levels of PPF. However, in this study design, attraction and dissemination was limited to short distances. To make this approach feasible for malaria vector control, stronger attractants that lure gravid females from longer distances, in landscapes with many water bodies, and better PPF delivery systems are needed.

[When Urban and Agricultural Activities Favor the Proliferation of Mosquito Nuisance and Vectors of Pathogens to Humans]

Big cities have thrived on all continents, so have domestic and industrial wastes not to mention the often irrational use of agricultural inputs (fertilizers and pesticides) detrimental to plants and animals. One hundred and eighty million tons of fertilizers and 2.4 million tons of pesticides are spread every year worldwide. Such pollutions, whether urban or rural, have a significant impact on the biology of mosquitoes. Today some urban spaces have properly become a land of plenty for mosquitoes. The combined use of fertilizer and pesticides in the country, quite paradoxically also favor their proliferation. Ironically the very reasons that account for the multitudes of mosquitoes are the exact reasons responsible for the depletion of biodiversity.

Mosquitocidal Chips Containing the Insect Growth Regulator Pyriproxyfen for Control of Aedes aegypti (Diptera: Culicidae)

Aedes aegypti were exposed to water treated with mosquitocidal chips containing the insecticide pyriproxyfen in a polymer formulation. Chips were tested under different conditions; different water volumes, in containers made of different material, and in water with different levels of organic matter. Treated chips caused 100% mortality of Ae. aegypti during their pupal stage independent of size or type of container, and the mount of organic matter contained in the water to which the mosquito larvae were exposed. When mosquitocidal chips were used in >25% of the oviposition containers within their cages, there was a significant control of the mosquito populations. Mosquitocidal chips worked in different environments, caused significant mosquito population decreases, and were effective in controlling Ae. aegypti.

Determination by chromatography and cytotoxotoxic and oxidative effects of pyriproxyfen and pyridalyl

Pyriproxyfen (PPF) is a larvicide, used to combat the proliferation of Aedes aegypti larvae. The objective of this study was to analyze the compounds of pyriproxyfen and pyridalyl (PYL) in a commercial larvicide to analyze the cytotoxic and oxidative effects of PPF and PYL. The toxic potential of PPF and PYL were assessed based on lethal concentration (LC₅₀) in Artemia salina, cytotoxicity based on the mitotic index and the chromosomal alterations in Allium cepa and the oxidative damage in Saccharomyces cerevisiae. The PPF and PYL compounds were identified by HPLC-PDA based on their retention times and spectral data. The wavelengths λ_max (258 nm) and (271 nm) of the UV spectrum of PYL and PPF and the retention times (R_T) (3.38 min) and (4.03 min), respectively. The toxicological potentials of PPF and PYL were significant at concentrations (1, 10, 100 and 1000 ppm), with an LC₅₀ of 48 h (0.5 ppm). PPF and PYL pointed out a cytotoxic effect in A. cepa at all concentrations (0.0001, 0.001, 0.01, 0.1, 1.0, 100 and 1000 ppm), genotoxic effect at concentrations only (0.0001; 0.1; 1; 100 and 1000 ppm), and mutagenic for concentrations (0.1, 100 and 1000 ppm). In relation S. cerevisiae, PPF e PYL prompted oxidative damage at concentrations (100 and 1000 ppm) in all strains (SODWT, Sod1, Sod2, Sod1Sod2, Cat1 and Sod1Cat1). Therefore, the PPF and PYL identificated in commercial larvicide by HPLC-PDA produced cytotoxic and oxidative effects that could cause health and ecosystem risks.

Time-dependent transcriptomic responses of Daphnia magna exposed to metabolic disruptors that enhanced storage lipid accumulation

The analysis of lipid disruption in invertebrates is limited by our poor knowledge of their lipidomes and of the associated metabolic pathways. For example, the mechanism by which exposure of the crustacean Daphnia magna to tributyltin, juvenoids, or bisphenol A increase the accumulation of storage lipids into lipid droplets is largely unknown/presently unclear. Here we analyze transcriptome changes subsequent to this lipid accumulation effect induced by either the pesticide pyriproxyfen (a juvenoid agonist), the plasticizer bisphenol A, or the antifouling agent tributyltin. Changes in the whole transcriptome were assessed after 8 and 24 h of exposure, the period showing the greatest variation in storage lipid accumulation. The three compounds affected similarly to a total of 1388 genes (965 overexpressed and 423 underexpressed transcripts), but only after 24 h of exposure. In addition, 225 transcripts became up-regulated in samples exposed to tributyltin for both 8 h and 24 h. Using D. melanogaster functional annotation, we determined that upregulated genes were enriched in members of KEGG modules implicated in fatty acid, glycerophospholipid, and glycerolipid metabolic pathways, as well as in genes related to membrane constituents and to chitin and cuticle metabolic pathways. Conversely, down-regulated genes appeared mainly related to visual perception and to oocyte development signaling pathways. Many tributyltin specifically upregulated genes were related to neuro-active ligand receptor interaction signaling pathways. These changes were consistent with the phetotypic effects reported in this and in previous studies that exposure of D. magna to the tested compounds increased lipid accumulation and reduced egg quantity and quality.

Efficacy of the In2Care® auto-dissemination device for reducing dengue transmission: study protocol for a parallel, two-armed cluster randomised trial in the Philippines

Background

Mosquito-borne viruses are imposing an ever increasing health burden worldwide. In addition to the recent Zika and chikungunya virus epidemics, dengue viruses have become the fastest growing problem with a 40-fold increase in the number of reported cases over the past five decades. Current mosquito control techniques involving larval source reduction, larviciding, and space spray of adulticides are costly, laborious, and of debatable efficacy. There remains an urgent need for the development of intervention methods that can be reasonably implemented in the context of modern day urbanisation. Auto-dissemination (AD) of insecticide by adult mosquitoes offers a potentially practical and useful tool in an integrated vector control programme. Recently, an immediately employable AD device, the In2Care® mosquito trap, has been commercialised and shows promise as an effective tool. However, there remains a lack of demonstration of epidemiological efficacy.

Methods/design

This trial aims to assess the extent to which implementation of In2Care® mosquito traps can reduce vector Aedes (Stegomyia) spp. adult mosquito densities and dengue virus transmission as measured by sequential sero-conversion rates in children 6–16 years of age in a dengue endemic location: Lipa City, Philippines. To achieve this, we will carry out a parallel, two-armed cluster randomised trial evaluating AD efficacy for reducing the incidence of dengue over a 2-year period with 4 consecutive months of vector control during peak dengue transmission each year.

Discussion

For decades, it has been commonly accepted that an integrated approach to mosquito control is required. The World Health Organization (WHO) Global Strategic Framework for Integrated Vector Management recommends a range of interventions, in combination, to increase control impact to reduce transmission. This efficacy trial of the first commercial product using the AD approach will be informative in assessing the general utility of AD in reducing not only adult vector densities but, more importantly, reducing the incidence of dengue. The AD technique may complement source reduction and larviciding campaigns by more efficiently targeting the most productive containers and those beyond human reach. If successful, this mosquito control strategy could prove an invaluable tool in the fight against urban mosquito vectors and a reduction in the burden of associated disease.

Trial registration

ISRCTN44272773. Registered on 31 January 2019.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3376-6) contains supplementary material, which is available to authorized users.

Autodissemination of pyriproxyfen suppresses stable populations of Anopheles arabiensis under semi-controlled settings

BACKGROUND

Autodissemination of pyriproxyfen (PPF), i.e. co-opting adult female mosquitoes to transfer the insect growth regulator, pyriproxyfen (PPF) to their aquatic habitats has been demonstrated for Aedes and Anopheles mosquitoes. This approach, could potentially enable high coverage of aquatic mosquito habitats, including those hard to locate or reach via conventional larviciding. This study demonstrated impacts of autodissemination in crashing a stable and self-sustaining population of the malaria vector, Anopheles arabiensis under semi-field conditions in Tanzania.

METHODS

Self-propagating populations of An. arabiensis were established inside large semi-field cages. Larvae fed on naturally occurring food in 20 aquatic habitats in two study chambers (9.6 × 9.6 m each), while emerging adults fed on tethered cattle. The mosquito population was monitored using emergence traps and human landing catches, each time returning captured adults into the chambers. Once the population was stable (after 23 filial generations), PPF dissemination devices (i.e. four clay pots each treated with 0.2-0.3 g PPF) were introduced into one of the chambers (treatment) and their impact monitored in parallel with untreated chamber (control).

RESULTS

Daily adult emergence was similar between control and treatment chambers, with average (± SE) of 14.22 ± 0.70 and 12.62 ± 0.74 mosquitoes/trap, respectively, before treatment. Three months post-treatment, mean number of adult An. arabiensis emerging from the habitats was 5.22 ± 0.42 in control and 0.14 ± 0.04 in treatment chambers. This was equivalent to > 97% suppression in treatment chamber without re-treatment of the clay pots. Similarly, the number of mosquitoes attempting to bite volunteers inside the treatment chamber decreased to zero, 6 months post-exposure (i.e. 100% suppression). In contrast, biting rates in control rose to 53.75 ± 3.07 per volunteer over the same period.

CONCLUSION

These findings demonstrate effective suppression of stable populations of malaria vectors using a small number of simple autodissemination devices, from which adult mosquitoes propagated pyriproxyfen to contaminate aquatic habitats in the system. This is the first proof that autodissemination can amplify treatment coverage and deplete malaria vector populations. Field trials are necessary to validate these results, and assess impact of autodissemination as a complementary malaria intervention.

High effectiveness of an adulticide-larvicide formulation for field control of sandflies (Diptera: Psychodidae) in the city of Clorinda, Argentina

In Argentina, Leishmania infantum (syn. L. chagasi) is the etiologic agent of human visceral leishmaniosis (HVL), and Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae) is the main vector. The objective of this study was to evaluate the effectiveness and residual effect of two commercial insecticide formulations, one with permethrin and pyriproxyfen as active ingredients (Dragon Max®) and the other with only permethrin (Flop®) for the control of sandflies. Both formulations were applied in chicken coops and other surroundings structures of the peridomicile of urban houses in Clorinda, Formosa (Argentina). Entomological monitoring was carried out weekly for 44 weeks after the intervention. The results showed great effectiveness and residual effect up to 21 weeks post-intervention for Dragon Max®. This result could be explained by the excellent larvicidal activity of the Insect Growth Regulator (IGR) pyriproxyfen against the immature forms of phlebotomines and by the delay on the restoration of the natural threshold of the vector population in treated sites.

An evaluation of efficacy of the auto-dissemination technique as a tool for Aedes aegypti control in Madeira, Portugal

Background

The frequency and intensity of arboviral epidemics is steadily increasing and posing an intractable public health burden. Current vector control methods are proving ineffectual and despite progress in the development of high technology approaches, there is an urgent need for the development of tools for immediate implementation. Several studies suggest that the auto-dissemination of pyriproxyfen (PPF) is a promising new approach to larviciding although there is little detail on the conditions under which it is optimally effective. Here, we evaluate the efficacy of the approach in urban and rural sites in Madeira, Portugal.

Results

Auto-dissemination of PPF through adapted Biogents Sentinel traps (BGSTs) resulted in a modest but consistent impact on both juvenile and adult mosquito populations, but with considerable spatial heterogeneity. This heterogeneity was related to the distance from the BGST dissemination station as well as the local density of adult mosquitoes. There was evidence that the impact of PPF was cumulative over time both locally and with gradual spatial expansion.

Conclusions

The density of adult mosquitoes and the spatial distribution of dissemination devices are key factors in mediating efficacy. In addition, urban topography may affect the efficiency of auto-dissemination by impeding adult mosquito dispersal. Further studies in a range of urban landscapes are necessary to guide optimal strategies for the implementation of this potentially efficacious and cost-effective approach to larviciding.

Insecticide pyriproxyfen (Dragón®) damage biotransformation, thyroid hormones, heart rate, and swimming performance of Odontophrynus americanus tadpoles

Odontoprynus americanus tadpoles were used to determine the safety concentration of pyriproxyfen (PPF) insecticide by acute and sublethal toxicity tests (nominal range tested 0.01 to 10 [± 15%] PPF mg/L). Median lethal concentration (LC₅₀) and no, and lowest-observed-effect concentrations (NOEC and LOEC, respectively) were calculated. We also assessed the effect on the activities of glutathione S-transferse (GST), acetylcholinesterase (AChE), and carboxylesterase (CbE) and compared to control (CO) tadpoles. Based on the 48-h NOEC value, two sublethal concentrations of PPF (0.01 and 0.1 mg/L) were assayed to detect effects on enzymes activities (GST and CbE), thyroid hormone's levels (triiodothyronine; T3 and thyroxine; T4), heart function, and tadpoles swimming behaviour. The results showed that the LC₅₀ values of O. americanus tadpoles were 3.73 PPF mg/L and 2.51 PPF mg/L at 24-h and 48-h, respectively (NOEC = 0.1 mg/L; LOEC = 1 mg/L, for both times). PPF concentrations at 48 h, induced enzymatic activities such as GST (212.98%-242.94%), AChE (142.15%-165.08%), and CbE (141.86%-87.14%) significantly respect to COs. During the 22 days of chronic PPF exposure, GST (0.01 mg/L 88%-153% NOEC), AChE (177.82% NOEC), and T4 (70% NOEC) also significantly increased respect to COs. Similarly, heart rate (fH) and ventricular cycle length (VV interval) in CO tadpoles were significantly higher than PPF treated. Finally, at NOEC tadpoles exhibited significant effects on the behavioral endpoint (swimming distance, mean speed, and global activity; P < 0.05).

The enantioselective environmental behavior and toxicological effects of pyriproxyfen in soil

We synthesized nine pyriproxyfen (PYR) metabolites and developed a chiral residual analysis method for PYR with its metabolites in five soils using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Soil degradation research showed that higher organic matter content and bigger soil particle size were conducive to the degradation of PYR and metabolites. Metabolite A 4'-OH-PYR was mainly found in five soils. PYR and metabolite A performed enantioselective degradation in soil with half-lives ranging from 2.11 d to 9.69 d and 2.80 d to 13.30 d, respectively. The activity of dehydrogenase, sucrase was inhibited and catalase activity was promoted under the disturbance of PYR. Urease was more sensitive to PYR with uncertain influences. Most soil enzymes were not restored to their initial active state after 120 d. The toxicity of metabolites to earthworms was greater than that of the parent compound PYR. This study provides the basic degradation and toxicity data of chiral pesticide PYR and its main metabolites in soil ecosystem, which is of great significance for guiding safe use and comprehensive evaluation of PYR on environmental risk.

Enantioselective dissipation of pyriproxyfen in soil under fertilizers use

An enantioselective method of pyriproxyfen enantiomers in fertilized soil was established on Lux Cellulose-3 column using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The effects of urea, potassium dihydrogen phosphate, organic fertilizer and compound fertilizer on the dissipation of pyriproxyfen in soil were investigated. Studies have shown that pyriproxyfen had a good linearity in the range of 0.050-7.5 μg/g. The method LODs and LOQs of two enantiomers were 0.0032-0.015 μg/g and 0.050 μg/g, respectively. The recoveries of two enantiomers ranged from 80.61% to 110.86%, intra-day together with inter-day RSDs of 1.38-12.52%. The results indicated that compound fertilizer could promote the dissipation of pyriproxyfen in soil, while the organic fertilizer, potassium dihydrogen phosphate and urea slowed down the dissipation of pyriproxyfen. Enantioselective dissipation of pyriproxyfen enantiomers occurred in blank soil and fertilized soil but performed not obviously. Pyriproxyfen almost not dissipated for 42 d when urea was added. These results revealed that the use of fertilizers would have impacts on the behaviors of this pesticide. The impacts were relatively complex which should be fully considered in future environmental risk evaluation.

Microcystin and pyriproxyfen are toxic to early stages of development in Rhamdia quelen: An experimental and modelling study

The recent increase of freshwater eutrophication has favored cyanobacteria blooms and consequently the increase of toxins such as microcystin-LR in aquatic environments, but few is know about the associated effect of toxin and other compounds. Pyriproxyfen is an insecticide indicated by WHO (World Health Organization) to control Aedes aegypti mosquito (vector of Dengue, Chikungunya and Zika diseases), however, the effects are not well described to non-target species, such as fish. The early life stages (ELS) of fish are more sensitive to chemical stress due to higher metabolic rate, immature immune system and high superficial area/volume ratio. In the current study, ELS of R. quelen a Neotropical fish were exposed to environmentally realistic concentrations of microcystin (1, 10 and 100 µg L^-1_; M1, M2 and M3 groups, respectively) from an algal extract, pyriproxyfen (1 and 10 µg L^-1, P1 and P2) and their association (co-exposure). The hatching, survival and larvae deformities were analyzed, and applied a mathematical model to evaluate the effects on the population size along further generations. Both compounds were toxic to embryos/larvae of fish, but the effects were more pronounced in M2, P1M2 and P2M1 for hatching and M2, P1M2, P2M1 and P1 for survival. Deformities prevailed in groups exposed to the chemicals at 48 hpf (hours post-fertilization) were suggestions of toxicological interaction in P1M2, P2M1 and P2M2 at 48 and 72 hpf. In 96 hpf, the levels of deformities were lower than in previous times. Model predicted population density over 100 years decreased to lower than 0.5 (50%) in all groups, except for P1M1, indicating risk of extinction. P1M2 had the worse results, followed by M2, P1M3 and P2M1. Cyanobacterial blooms can lead to microcystin-LR levels higher than M2 (10 µg L^-1), and the suggestion of toxicological interaction with pyriproxyfen is relevant because both compounds may potentially coexist in aquatic environments. Finally, mathematical models may provide an ecological interpretation of the risk of exposure of fish.

Alternative insecticides for larval control of the dengue vector Aedes aegypti in Lao PDR: insecticide resistance and semi-field trial study

BACKGROUND

The mosquito Aedes aegypti is the primary vector of several arboviruses, such as dengue, chikungunya and Zika, and represents a major public health problem in Southeast Asia. In Laos, where dengue is reemerging, several Ae. aegypti populations from the capital Vientiane have shown resistance to the organophosphate temephos, a commonly-used larvicide for public health interventions.

METHODS

Here, we tested the insecticide susceptibility of a wild larval population of Ae. aegypti against Bacillus thuringiensis israelensis (Bti), diflubenzuron, pyriproxyfen and spinosad. Residual efficacies of Bti (VectobacWG®), diflubenzuron (Killmos®) and temephos (Abate®) were then evaluated under simulated field conditions against the wild Ae. aegypti population.

RESULTS

The larval bioassays showed that the wild Ae. aegypti strain was moderately resistant to temephos and spinosad (resistance ratio, RR < 5) and fully susceptible to the other insecticides (RR = 1). The simulated field trial bioassays showed that all of the insecticides tested remained above the WHO acceptable larvicide threshold after 28 weeks.

CONCLUSIONS

These results suggest that Bti and diflubenzuron may be promising alternative larvicides for controlling dengue vectors in water-storage containers in Laos, especially against Ae. aegypti populations, in which resistance to temephos has been detected.

Allocation of glycerolipids and glycerophospholipids from adults to eggs in Daphnia magna: Perturbations by compounds that enhance lipid droplet accumulation

Analysis of the disruptive effects of chemicals on lipids in invertebrates is limited by our poor knowledge of the lipid metabolic pathways and the complete lipidome. Recent studies shown that juvenoids and bisphenol A disrupted the dynamics of lipid droplets in the crustacean Daphnia magna. This study used ultra-high performance liquid chromatography/time-of-flight mass spectrometry (UHPLC/TOFMS) to study how juvenoids (pyriproxyfen and methyl farnesoate) and bisphenol A disrupt the dynamics of glycerophospholipids and glycerolipids in Daphnia adults and their allocation to eggs. Lipidomic analysis identified 234 individual lipids corresponding to three classes of glycerolipids, seven of glycerophospholipids, and one of sphingolipids, of which 194 changed according to the chemical treatments and time. Adult females in the control and bisphenol A treatment groups had low levels of triacylglycerols but high levels of glycerophospholipids, whereas those in the juvenoid treatment groups had high levels of triacylglycerols and low levels of glycerophospholipids. The opposite trend was observed for the lipid contents in the eggs produced. Because the juvenoids reduced reproduction dramatically, the females allocated less triacylglycerols to their eggs than the controls did. Interestingly, females exposed to bisphenol A allocated less triacylglycerols to their eggs despite producing a similar number of eggs as that of the controls. Thin-layer chromatography analyses confirmed the UHPLC/TOFMS results and allowed qualitative determination of cholesterol, which was also accumulated in females exposed to the juvenoids.