Evaluation of different formulations of IGRs against Aedes albopictus and Culex quinquefasciatus (Diptera: Culicidae)

Effect of α-cypermethrin and pirimiphos-methyl on wing morphology of Tribolium castaneum (Herbst) and T. confusum Jacquelin du Val: a comparative study

Tribolium castaneum (Herbst) and Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) are widespread and serious pests of stored products. Various insecticides are applied aiming to effectively manage both species. Here, two insecticides are tested, the pyrethroid α-cypermethrin and the organophosphate pirimiphos-methyl, hypothesizing that they can lead to morphological changes in the certain body parts of the adult offspring of treated T. castaneum and T. confusum parental female adults. For this purpose, the geometric morphometric method to the elytra and hindwings was applied. Both males and females were included in the analysis. The results showed that adult individuals of T. confusum showed higher tolerance to both insecticides compared to T. castaneum adults. This finding is reflected in analyses of both pairs of wings in T. confusum where changes in shape were negligible. The hindwings of T. castaneum experienced deformations to both insecticides. More significant changes in wing shape were observed in the α-cypermethrin treatment compared to pirimiphos-methyl. In the case of T. castaneum, even the shortest exposure to insecticides (5 min) is enough to provoke shape changes in the hindwings. Deformities in offspring, caused after treatment of their parents with insecticides, could moderate the frequency of insecticidal applications in storages.

Sub-Lethal Effects of Pirimiphos-Methyl Are Expressed to Different Levels in Wings of Three Stored-Product Coleopterans: A Geometric Morphometrics Investigation

Tenebrio molitor L. (Coleoptera: Tenebrionidae), Prostephanus truncatus (Horn), and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) are noxious insect pests of grains in storages. Pirimiphos-methyl is widely used to protect grains at the post-harvest stage. However, the sub-lethal impact of this active ingredient on the offspring of all three coleopterans remains unknown. Thus, mated females of each species were exposed separately to pirimiphos-methyl at short exposures (30 min, 3, 5, 8, 16, 24, and 36 h), where the elytra and hindwings of the adult progeny were analyzed with the geometric morphometrics method. Males and females of all species were incorporated into the analysis. The results revealed variability among species. Tenebrio molitor was the most sensitive among three species, displaying significant deformations in the elytra and hindwings. Males had more conspicuous morphological changes than females. Prostephanus truncatus hindwings exhibited deformities after 36 h of exposure to pirimiphos-methyl. In contrast, R. dominica offspring were not affected by pirimiphos-methyl. In light of our findings, organophosphorus insecticides may cause variable sub-lethal effects to stored-product insects. This issue may lead to different insecticidal treatments according to the targeted stored-product species.

Evaluation of Pyriproxyfen Effects on Aedes aegypti and Predatory Mosquito Toxorhynchites rutilus (Diptera: Culicidae)

Control of mosquito vectors of pathogens remains heavily dependent on the application of conventional insecticides. Pyriproxyfen (PPF) is a novel insecticide that has been proposed for use in autodissemination techniques to control mosquito vectors. The use of PPF can inhibit adult emergence but does not inhibit larval development. This feature is favorable for controlling Aedes aegypti because PPF has the potential to work in combination with natural sources of mortality (competition, predation) during the immature stages, and other control methods, including biocontrol agents that further suppress recruitment of adult mosquitoes. However, the PPF effects on life-history traits of Ae. aegypti in comparison to predatory mosquito Toxorhynchites rutilus, a source of mortality, are not fully understood. Here, we show that larval exposure to PPF concentrations that inhibit 50-90% of adult emergence in Ae. aegypti had a negligible effect on adult emergence and lifespan of Tx. rutilus. Weights of adult Ae. aegypti and Tx. rutilus were not influenced by PPF. These findings suggest that the use of PPF to control mosquito vectors may have low effects on mosquito biocontrol agents. Our results extend and confirm earlier data showing that PPF has potential to implement with Tx. rutilus to suppress Ae. aegypti and provide an additional advantage of PPF use in autodissemination control strategies.

Mosquitoes Larvicidal Activity of Ocimum kilimandscharicum Oil Formulation under Laboratory and Field-Simulated Conditions

Simple Summary

Mosquitoes are vectors of many severe diseases, notably malaria, yellow as well as dengue fever, and lymphatic filariasis. Vector control with synthetic chemical insecticides has been associated with resistance development and undesirable human and ecological effects. Ocimum kilimandscharicum oil formulation was evaluated for larvicidal activity against third instar mosquito larvae in the laboratory. The formulation was then compared with Bacillus thuringiensis subsp. israelensis (Bti) granules on An. gambiae larvae under field-simulated field trials. The LC₅₀ for O. kilimandscharicum oil after 24 h against third instar larvae of An. gambiae was 0.74 ppm while for the emulsified O. kilimandscharicum oil formulation against third instar larvae of An. gambiae and An. arabiensis was 0.07 and 0.31 ppm, respectively. The high bioactivity and sublethal toxic effects to offspring of treated mosquito larvae in terms of the disruption of larval morphological aspects suggest its high potential as a botanical larvicide for the control of disease vectors. The bioactive formulation had the advantage of high solubility in aqueous media; it is also easily produced, ecofriendly, and low-cost. Moreover, because O. kilimandscharicum can easily be widely cultivated and has high EO yields, it may provide a valuable alternative for the effective and eco-friendly control of disease vectors among developing and developed communities.

Abstract

Mosquitoes are vectors of many severe diseases, including malaria, yellow as well as dengue fever, and lymphatic filariasis. The use of synthetic chemical insecticides for mosquito control has been associated with resistance development and detrimental human, and ecological effects. For a safer alternative, the emulsified Ocimum kilimandscharicum oil formulation was evaluated for its larvicidal activity. The oil was analyzed by GC and GC/MS. The formulations were evaluated against third instar mosquito larvae in the laboratory and later compared with Bacillus thuringiensis subsp. israelensis against An. gambiae under field-simulated conditions. Thirty-nine compounds were identified in the oil, the main ones being D-camphor (36.6%) and limonene (18.6%). The formulation showed significant larval mortalities against An. gambiae and An. arabiensis larvae with LC₅₀ of 0.07 and 0.31 ppm, respectively, at 24 h. Under the field-simulated trial, within 24 h, the formulation showed 98% mortality while Bti had achieved 54%. On day three, it caused 100% mortality while Bti achieved 76.5%. The high bioactivity and sublethal toxic effects to offspring of treated mosquito larvae, in terms of disruption of larval morphological aspects, suggest the high potential of the formulation as a botanical larvicide. The formulation, thus, may provide a valuable alternative for the effective and eco-friendly control of disease vectors.

Statewide Efficacy Assessment of Insect Growth Regulators Against Aedes albopictus (Diptera: Culicidae) in Sabah, Malaysia: An Alternative Control Strategy?

The efficacy of three groups of insect growth regulators, namely juvenile hormone mimics (methoprene and pyriproxyfen), chitin synthesis inhibitors (diflubenzuron and novaluron), and molting disruptor (cyromazine) was evaluated for the first time, against Aedes albopictus Skuse (Diptera: Culicidae) larvae from 14 districts in Sabah, Malaysia. The results showed that all field populations of Ae. albopictus were susceptible towards methoprene, pyriproxyfen, diflubenzuron, novaluron, and cyromazine, with resistance ratio values ranging from 0.50-0.90, 0.60-1.00, 0.67-1.17, 0.71-1.29, and 0.74-1.07, respectively. Overall, the efficacy assessment of insect growth regulators in this study showed promising outcomes and they could be further explored as an alternative to conventional insecticides.

Heterodissemination: precision insecticide delivery to mosquito larval habitats by cohabiting vertebrates

Conventional larvicide delivery strategies originally developed for permanent and floodwater mosquitoes have proved suboptimal in the small, scattered, and cryptic larval habitats preferred by container-inhabiting Aedes mosquitoes. New methods such as autodissemination, wherein adult mosquitoes spread insecticides to their own larval habitats, have been under study. Another novel delivery method termed heterodissemination, i.e. larvicide delivery by other species sharing the same habitats, has also been proposed. We conducted a proof-of-concept study with four independent experiments using American bullfrogs (Lithobates catesbeianus) and green frogs Lithobates clamitans as carriers of pyriproxyfen, an insect growth regulator, under semi-field conditions in three different locations, two in New Jersey, and one in Utah. Frogs with attached slow-release pyriproxyfen tablets were introduced into outdoor enclosures with water containers. Water samples from the containers were periodically tested using larval Aedes albopictus and Culex pipiens mosquitoes to assess mortality and percent eclosure inhibition. Overall pupal mortality [95% credible intervals] estimated by Bayesian analysis for the treatment group was 73.4% [71.3–75.2] compared to 4.1% [2.9–5.5] for the control group. Mortality within treatment groups in four different experiments ranged from 41 to 100%, whereas control mortalities ranged from 0.5% to 11%. We conclude that heterodissemination is a promising and effective approach deserving of further study.

Molecular characterization and enzyme inhibition studies of NADP+- farnesol dehydrogenase from diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Juvenile hormone III (JH III) plays an important role in insect reproduction, development, and behavior. The second branch of JH III production includes oxidation of farnesol to farnesal by farnesol dehydrogenase. This study reported the identification and characterization of Plutella xylostella farnesol dehydrogenase (PxFoLDH). Our results showed that PxFoLDH belongs to the short-chain dehydrogenase/reductase superfamily, consisting of a single domain with a structurally conserved Rossman fold, an NAD(P) (H)-binding region and a structurally diverse C-terminal region. The purified enzyme displayed maximum activity at 55$\ $°C with pH 9.5 and was stable in the temperature below 70$\ ^\circ $C. PxFoLDH was determined to be a monomer with a relative molecular weight of 27 kDa and highly specific for trans, trans-farnesol, and NADP+. Among analog inhibitors tested, farnesyl acetate was the most effective inhibitor with the lowest Ki value of 0.02 µm. Our findings showed this purified enzyme may represent as NADP+-farnesol dehydrogenase.

Use of pyriproxyfen in control of Aedes mosquitoes: A systematic review

Dengue is the most rapidly spreading arboviral disease in the world. The current lack of fully protective vaccines and clinical therapeutics creates an urgent need to identify more effective means of controlling Aedes mosquitos, principally Aedes aegypti, as the main vector of dengue. Pyriproxyfen (PPF) is an increasingly used hormone analogue that prevents juvenile Aedes mosquitoes from becoming adults and being incapable of transmitting dengue. The objectives of the review were to (1) Determine the effect of PPF on endpoints including percentage inhibition of emergence to adulthood, larval mortality, and resistance ratios; and (2) Determine the different uses, strengths, and limitations of PPF in control of Aedes. A systematic search was applied to Pubmed, EMBASE, Web of Science, LILACS, Global Health, and the Cochrane database of Systematic Reviews. Out of 1,369 records, 90 studies met the inclusion criteria. Nearly all fit in one of the following four categories 1) Efficacy of granules, 2) Auto-dissemination/horizontal transfer, 3) use of ultra-low volume thermal fogging (ULV), thermal fogging (TF), or fumigant technologies, and 4) assessing mosquito resistance. PPF granules had consistently efficacious results of 90-100% inhibition of emergence for up to 90 days. The evidence is less robust but promising regarding PPF dust for auto-dissemination and the use of PPF in ULV, TF and fumigants. Several studies also found that while mosquito populations were still susceptible to PPF, the lethal concentrations increased among temephos-resistant mosquitoes compared to reference strains. The evidence is strong that PPF does increase immature mortality and adult inhibition in settings represented in the included studies, however future research should focus on areas where there is less evidence (e.g. auto-dissemination, sprays) and new use cases for PPF. A better understanding of the biological mechanisms of cross-resistance between PPF, temephos, and other insecticides will allow control programs to make better informed decisions.

Use of Novaluron-Based Autocidal Gravid Ovitraps to Control Aedes Dengue Vector Mosquitoes in the District of Gampaha, Sri Lanka

Dengue is the most important mosquito-borne viral infection in Sri Lanka causing an enormous social and economic burden in the country. In the absence of therapeutic drugs and the developed vaccines are under investigation, vector control is the best strategy to reduce the disease transmission. Therefore, the development of novel tools to control dengue vector mosquitoes has become the need of the hour. Novaluron is a recently developed Insect Growth Regulator (IGR) which inhibits chitin synthesis in immature stages of insects. The aim of the study was to identify the efficacy of a simple and cost-effective Autocidal Gravid Ovitrap (AGO) developed using Novaluron to control dengue outbreaks in the District of Gampaha, Sri Lanka. Laboratory and semifield experiments were performed to identify the activity range, optimum field dosage, and residual effects of Novaluron following the World Health Organization guidelines, and field experiments were performed in the Ragama Medical Officer of Health (MOH) area. Two study areas 800 m apart were selected and assigned as treated and control areas randomly. In each study area, 30 households were selected randomly. Each household was given two ovitraps, one placed indoors and the other placed outdoors. Mortality and survival counts were recorded separately for one-year time period and data were analyzed using a two-way repeated measures analysis of variance model. During the laboratory experiments, the adult emerging inhibition was 100% in all tested concentrations. The optimum field dosage was 2 ppm and the residual effect was 28 days. In the field experiments, significantly higher mortality counts were recorded in treated areas both indoor- and outdoor-placed AGOs. Two-factor repeated measures ANOVA followed by Tukey's test confirmed that the mean mortality count is high for the developed AGOs both indoor and outdoor settings. The developed AGO can be deployed to control both indoor and outdoor dengue vector mosquito populations, and in dengue-risk areas, the ovitrap will be supportive to local health authorities to enhance the efficiency of future vector control programs.

Does the exposure of parental female adults of the invasive Trogoderma granarium Everts to pirimiphos-methyl on concrete affect the morphology of their adult progeny? A geometric morphometric approach

Insecticidal applications may result to morphological deformations upon exposed insects or their offspring production. In the present study, we tested whether pirimiphos-methyl can induce deformities to wings of progeny production of the invasive khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae) when its parental female adults have been treated with this organophosphorus active ingredient. For that purpose, we analysed both elytra and hindwings of both sexes of T. granarium progeny production by using the geometric morphometrics method. Our results showed that the wings of progeny of the pirimiphos-methyl-treated T. granarium parental female adult individuals suffered certain changes in their usual shape depending on size. Deformations occurred on both pairs of wings, but changes were more noticeable on the hindwings. A longer than 5-h exposure of parental female adults to pirimiphos-methyl, resulted in progeny with more deformed wings than in those individuals emerged after the exposure of their parental female adults in shorter periods on the toxicant. Generally, wings of both sexes were sensitive to pirimiphos-methyl, distinguishing the control group from the insecticidal treatments. The existence of deformed adults could be a useful indicator of earlier insecticidal applications as surface treatments and/or grain protectants in the storage facilities.

Exploring the Insecticide and Acaricide Potential of Development Regulators obtained from Restinga vegetation from Brazil

As a part of our continuing search for insect and arthropod development regulators from Brazilian restinga vegetation of the Rio de Janeiro State, crude extracts, purified fractions and essential oils were submitted to screening tests seeking for biological activities on the development of the insects Rhodnius prolixus, Dysdercus peruvianus, Oncopeltus fasciatus and Rhipicephalus (Boophilus) microplus. Up to now, 102 secondary metabolites have been detected in the fractions, among them monoterpenes, sesquiterpenes and two triterpenes which were obtained from the species, Eugenia sulcata, Pilocarpus spicatus, Manilkara subsericea, Myrciaria floribunda and Zanthoxylum caribaeum. These secondary plant metabolites are considered of interest for the use of studies related to arthropod endocrinology, vector-parasite interaction system, and population control of vector insect and agricultural pest. The observed biological activities were surprisingly high, involving increased mortality, molting and metamorphosis inhibition, paralysis, corporeal deformities, apparition of permanent nymphs, of adultoids and juvenoids, partial or total inhibition of oviposition and egg hatching. These compounds are now being studied further to determine if they may or may not be useful in controlling insect populations and/or interfere with the life cycle and vector transmission of parasites to animal and human populations.

Epidemiological trends and risk factors associated with dengue disease in Pakistan (1980-2014): a systematic literature search and analysis

BACKGROUND

Dengue is becoming more common in Pakistan with its alarming spreading rate. A historical review needs to be carried out to find the root causes of dengue dynamics, the factors responsible for its spread and lastly to formulate future strategies for its control.

METHODS

We searched (January, 2015) all the published literature between 1980 and 2014 to determine spread/burden of dengue disease in Pakistan.

RESULTS

A total of 81 reports were identified, showing high numbers of dengue cases in 2010, 2011, and 2013. The tendency of dengue to occur in younger than in older age groups was evident throughout the survey period and all four serotypes were recorded, with DENV1 the least common. Most dengue hemorrhagic fever (DHF) cases fell in the 20-45 years age range. High frequencies tended to be observed first in the Southern coastal region characterized by mild winters and humid warm summers and then the disease progressed towards the lowland areas of the Indus plain with cool winters, hot summers and monsoon rainfall. Based on this survey, new risk maps and infection estimates were identified reflecting public health burden imposed by dengue at the national level.

CONCLUSIONS

Our study showed that dengue is common in the three provinces of Pakistan, i.e., Khyber Pakhtunkhwa (KP), Punjab and Sindh. Based on the literature review as well as on our study analysis the current expansion of dengue seems multifactorial and may include climate change, virus evolution, and societal factors such as rapid urbanization, population growth and development, socioeconomic factors, as well as global travel and trade. Due to inadequate remedial strategies, effective vector control measures are essential to target the dengue vector mosquito where high levels of human-vector contact occur. The known social, economic, and disease burden of dengue is alarming globally and it is evident that the wider impact of this disease is grossly underestimated. An international multi-sectoral response, outlined in the WHO Global Strategy for Dengue Prevention and Control, 2012-2020, is now essential to reduce the significant influence of this disease in Dengue endemic areas. Overall gaps were identified in knowledge around seroprevalence, dengue incidence, vector control, genotype evolution and age-stratified serotype circulation.