Widespread Resistance to Temephos in Aedes aegypti (Diptera: Culicidae) from Mexico

Organic synthetic insecticides continue to be part of the arsenal for combating vector-borne diseases in Mexico. Larvicides are a fundamental part of the process in programs for mosquito control, temephos being one of the most widely used in Mexico. In the present study, we analyzed the frequency of temephos resistance in twenty-three Aedes aegypti populations using the discriminating concentration (DC) of 0.012 mg/L. We also tested 5× DC (0.6 mg/L) and 10× DC (0.12 mg/L) of temephos. The resistance distribution to temephos was interpolated to unsampled sites using the inverse distance weighting (IDW) method. The populations of Ae. aegypti showed a high frequency of resistance (1× DC) with mortality rates below 93% in 22 of the 23 populations analyzed. Moderate resistance intensity (5× DC) was found in 78% of the populations, and high intensity (10× DC) in 30%. Predicted mortality was below 60% in the populations of the Pacific Coast, along the Gulf of Mexico, and in the state of Coahuila in Northeastern Mexico in relation to 1× DC; the Pacific Coast and Northeast patterns hold for 5× and 10× DC. The results suggest the need for rotation of the larvicide to effectively control the larval populations of the vector in the country.

Does prior exposure to larvicides influence dengue virus susceptibility in Aedes aegypti (Diptera: Culicidae)?

Control of mosquito vector populations is primarily intended to reduce the transmission of pathogens they transmit. Use of chemical controls, such as larvicides, can have unforeseen consequences on adult traits if not applied properly. The consequences of under application of larvicides are little studied, specifically the impacts on pathogen infection and transmission by the vectors that survive exposure to larvicides. We compared vector susceptibility of Aedes aegypti (L.) for dengue virus, serotype 1 (DENV-1) previously exposed as larvae to an LC50 of different classes of insecticides as formulated larvicides. Larval exposure to insect growth regulators (methoprene and pyriproxyfen) significantly increased susceptibility to infection of DENV-1 in Ae. aegypti adults but did not alter disseminated infection or transmission. Larval exposure to temephos, spinosad, and Bti did not increase infection, disseminated infection, or transmission of DENV-1. Our findings describe a previously under observed phenomenon, the latent effects of select larvicides on mosquito vector susceptibility for arboviruses. These data suggest that there are unintended consequences of sublethal exposure to select larvicides that can influence susceptibility of Ae. aegypti to DENV infection, and indicates the need for further investigation of sublethal effects of insecticides on other aspects of mosquito biology, especially those parameters relevant to a mosquitoes ability to transmit arboviruses (life span, biting behavior, extrinsic incubation period).

Testing the susceptibility of larval stages of Simulium to temephos and Bacillus thuringiensis var israelensis in Germany and Northern Cameroon

Assays to evaluate the susceptibility of Simulium larvae to temephos and Bacillus thuringiensis var israelensis (Bti) were carried out by setting-up an in vitro laboratory test ('bio assay') and a semi-natural test ('système de goutières') to assess the LC50/LC90 values. Larvae of Simulium species in Cameroon (S. damnosum s.l., S. hargreavesi, S. vorax and S. cervicornutum) and (S. (Odagmia) ornatum and S. latipes) in Germany were identified and tested. In the bio-assay, 50 larvae were exposed for 10 min to concentrations from 0.01 to 10 ppm. For the Simulium from Germany, the LC50 (LC90) values after 3 and 6 h were 3.1 (27.9) and 0.14 (1.26) ppm for temephos and for Bti 7.8 (70.2) and 1.7 (15.3) ppm, respectively. For Cameroonian species, the values of LC50 (LC90) were lower, that is, 0.42 (8.04), 0.14 (2.70) and 0.073 (1.38) ppm, respectively, after 3, 6 and 12 h for temephos. In a semi natural condition, the LC50 of 10 min of application of temephos was 0.84 ppm after 3 h and a working solution (2.6 L) of Bti killed 50% after 6 h. To detect an upcoming of any resistance as it happened in Ivory Coast, a study of the occurrence resistance genes should be implemented.

Altered phagocytic capacity due to acute exposure and long-term post-exposure to pesticides used for vector-borne disease as dengue

Spinosad and temefos are widely used pesticides for chemical control of dengue vector-borne disease (Aedes aegypti). The aim of this study was to compare the effect of acute exposure (7 days) to spinosad (0.5 mg A.I. L^-1) and temefos (10 mg A.I. L^-1), concentrations used by the Mexican Ministry of Health, on phagocytic capacity (PC) of mononuclear cells of guppies fish (Poecilia reticulata), as well as to assess PC in fish, at 96 days after exposure to those pesticides. Obtained results indicated that spinosad did not alter PC, while an acute exposure to temefos significantly affected phagocytosis and this parameter was maintained downed even 96 days after the acute exposure, suggesting that the immunotoxic effects of temefos may be chronic.

in West Sumatra, Indonesia

<b>Background and Objective:</b> Dengue cases have increased while the spread is getting broader worldwide. Temephos has been frequently used to control the larvae of the <i>Aedes aegypti</i> L., the primary vector of dengue. The intensive use of this larvicide has given rise to resistance. This study aims to determine the susceptibility status of <i>Ae. aegypti</i> to temephos and examine the two mutations (F290V and F455W) that possibly occur in the <i>Ace-1</i> gene of <i>Ae. aegypti</i> from Salido Sub-District, IV Jurai District, Pesisir Selatan Regency. <b>Materials and Methods:</b> The susceptibility test was performed referring to a standard method of the World Health Organization, followed by a molecular test (polymerase chain reaction) and sequencing. <b>Results:</b> The results showed that the larvae of <i>Ae. aegypti</i> have been tolerant to temephos (0.012 mg L<sup></sup><sup>1</sup>) with a percentage of larval mortality of 91.67%. The sequencing analysis in the <i>Ace-1</i> gene revealed the absence of F290V and F455W mutation in temephos-resistant <i>Ae. aegypti</i>, but a point mutation was detected at codon 506. This mutation shifts the ACA codon to ACT, but still codes for the same amino acid, threonine. <b>Conclusion:</b> Our study indicates the presence of other resistance mechanisms in the major dengue vector of the Salido District. Implementation of the alternative population control strategy is required to prevent the temephos resistance further.

Enhancement of Temephos and Deltamethrin Toxicity by Petroselinum crispum Oil and its Main Constituents Against Aedes aegypti (Diptera: Culicidae)

Previous work presented the profound antimosquito potential of Petroselinum crispum essential oil (PEO) against either the pyrethroid-susceptible or resistant strains of Aedes aegypti. This plant oil also inhibited the activity of acetylcholinesterase and mixed-function oxidases significantly, thus suggesting its potential as a synergist for improving mosquitocidal efficacy of insecticidal formulations. This study investigated the chemical composition, larvicidal activity, and potential synergism with synthetic insecticides of PEO and its main compounds for the purpose of interacting with insecticide resistance in mosquito vectors. The chemical profile of PEO, obtained by GC-MS analysis, showed a total of 17 bioactive compounds, accounting for 99.09% of the whole oil, with the most dominant constituents being thymol (74.57%), p-cymene (10.73%), and γ-terpinene (8.34%). All PEO constituents exhibited promising larvicidal effects, with LC50 values ranging from 19.47 to 59.75 ppm against Ae. aegypti, in both the pyrethroid-susceptible and resistant strains. Furthermore, combination-based bioassays revealed that PEO, thymol, p-cymene, and γ-terpinene enhanced the efficacy of temephos and deltamethrin significantly. The most effective synergist with temephos was PEO, which reduced LC50 values to 2.73, 4.94, and 3.28 ppb against MCM-S, PMD-R, and UPK-R, respectively, with synergism ratio (SR) values of 1.33, 1.38, and 2.12, respectively. The best synergist with deltamethrin also was PEO, which reduced LC50 values against MCM-S, PMD-R, and UPK-R to 0.008, 0.18, and 2.49 ppb, respectively, with SR values of 21.25, 9.00, and 4.06, respectively. This research promoted the potential for using essential oil and its principal constituents as not only alternative larvicides, but also attractive synergists for enhancing efficacy of existing conventional insecticides.

Insecticide resistance selection and reversal in two strains of Aedes aegypti

Background: Laboratory reared mosquito colonies are essential tools to understand insecticide action. However, they differ considerably from wild populations and from each other depending on their origin and rearing conditions, which makes studying the effects of specific resistance mechanisms difficult. This paper describes our methods for establishing multiple resistant strains of Aedes aegypti from two colonies as a new resource for further research on metabolic and target site resistance. Methods: Two resistant colonies of Ae. aegypti, from Cayman and Recife, were selected through 10 generations of exposure to insecticides including permethrin, malathion and temephos, to yield eight strains with different profiles of resistance due to either target site or metabolic resistance. Resistance ratios for each insecticide were calculated for the selected and unselected strains. The frequency of kdr alleles (F1534C and V1016I) in the Cayman strains was determined using TaqMan assays. A comparative gene expression analysis among Recife strains was conducted using qPCR in larvae (CCae3A, CYP6N12, CYP6F3, CYP9M9) and adults (CCae3A, CYP6N12, CYP6BB2, CYP9J28a). Results: In the selected strain of Cayman, mortality against permethrin reduced almost to 0% and kdr became fixated by 5 generations. A similar phenotype was seen in the unselected homozygous resistant colony, whilst mortality in the susceptible homozygous colony rose to 82.9%. The Recife strains showed different responses between exposure to adulticide and larvicide, with detoxification genes in the temephos selected strain staying similar to the baseline, but a reduction in detoxification genes displayed in the other strains. Conclusions: These selected strains, with a range of insecticide resistance phenotypes and genotypes, will support further research on the effects of target-site and/or metabolic resistance mechanisms on various life-history traits, behaviours and vector competence of this important arbovirus vector.

Insecticide resistance selection and reversal in two strains of Aedes aegypti

Background: Laboratory reared mosquito colonies are essential tools to understand insecticide action. However, they differ considerably from wild populations and from each other depending on their origin and rearing conditions, which makes studying the effects of specific resistance mechanisms difficult. This paper describes our methods for establishing multiple resistant strains of Aedes aegypti from two colonies as a new resource for further research on metabolic and target site resistance. Methods: Two resistant colonies of Ae. aegypti, from Cayman and Recife, were selected through 10 generations of exposure to insecticides including permethrin, malathion and temephos, to yield eight strains with different profiles of resistance due to either target site or metabolic resistance. Resistance ratios for each insecticide were calculated for the selected and unselected strains. The frequency of kdr alleles in the Cayman strains was determined using TaqMan assays. A comparative gene expression analysis among Recife strains was conducted using qPCR in larvae (CCae3A, CYP6N12, CYP6F3, CYP9M9) and adults (CCae3A, CYP6N12, CYP6BB2, CYP9J28a). Results: In the selected strain of Cayman, mortality against permethrin reduced almost to 0% and kdr became fixated by 5 generations. A similar phenotype was seen in the unselected homozygous resistant colony, whilst mortality in the susceptible homozygous colony rose to 82.9%. The Recife strains showed different responses between exposure to adulticide and larvicide, with detoxification genes in the temephos selected strain staying similar to the baseline, but a reduction in detoxification genes displayed in the other strains. Conclusions: These selected strains, with a range of insecticide resistance phenotypes and genotypes, will support further research on the effects of target-site and/or metabolic resistance mechanisms on various life-history traits, behaviours and vector competence of this important arbovirus vector.

Comparative toxicity of larvicides and growth inhibitors on Aedes aegypti from select areas in Jamaica

Insecticide resistance has become problematic in tropical and subtropical regions, where Aedes mosquitoes and Aedes-borne arboviral diseases thrive. With the recent occurrence of chikungunya and the Zika virus in Jamaica, the Ministry of Health and Wellness, Jamaica, partnered with the United States Agency for International Development to implement multiple intervention activities to reduce the Aedes aegypti populations in seven parishes across the island and to assess the susceptibility of collected samples to various concentrations of temephos, Bacillus thuringiensis subsp. israelensis, (Bti), diflubenzuron and methoprene. Of the insecticides tested, only temephos has been used in routine larviciding activities in the island. The results showed that only temephos at concentrations 0.625 ppm and Bti at concentrations 6-8 ppm were effective at causing 98-100% mortality of local Ae. aegypti at 24 h exposure. Surprisingly, the growth inhibitors diflubenzuron and methoprene had minimal effect at preventing adult emergence in Ae. aegypti larvae in the populations tested. The results demonstrate the need for insecticide resistance testing as a routine part of vector control monitoring activies in order to determine useful tools that may be incorporated to reduce the abundance of Ae. aegypti.

Evaluation of the Persistence of Three Larvicides Used To Control Aedes aegypti In Arapiraca, Northeastern Brazil

The chemical control of the mosquito Aedes aegypti is a great challenge worldwide, since several populations of this species are already resistant to traditional insecticides, such as temephos. In Brazil, alternative larvicides, such as Bacillus thuringiensis israelensis (Bti) and pyriproxyfen, have been used more recently. In this study we evaluated the persistence of pyriproxyfen (Sumilarv 0.5%G), 2 commercial formulations of Bti (Vectobac WDG and Vectobac G), and temephos (Fersol 1G) under field and simulated field conditions with treatments exposed to sun and shadow. In the field tests, the 2 formulations of Bti presented less persistence in the 8th wk of evaluation (46% and 37% positivity) compared with temephos (3.6% and 6.8% positivity) and Sumilarv (6.6% and 3.8% positivity) in containers exposed to the sun and shadow, respectively. In the simulated field trial, temephos and the 2 formulations of Bti presented high persistence (100% mortality at 8th wk) when applied in the water box and in deposits placed in the shade. In containers exposed to the sun, the persistence of these products was lower (>80% mortality by temephos after 4 wk, Bti formulations for 3 wk, and Sumilarv for 6 wk). Based on these data, however, Sumilarv presented better performance in the containers exposed to the sun than the 2 formulations of Bti (Vectobac G and Vectobac WDG), which were affected by the sun.

Resistance Status of Aedes aegypti to Deltamethrin, Malathion, and Temephos in Ecuador

In Ecuador, the status of insecticide resistance for Aedes aegypti, the principal arboviral vector in the country, has not been previously evaluated. The aim of this research was to describe the resistance status of Ae. aegypti to the principal insecticides used for vector control in provinces with high reports of arboviral clinical cases. This was a descriptive study performed on Ae. aegypti collected from 2016 to 2017 in 14 localities of Ecuador. The larvae were reared and tested using bioassays applying the adulticides malathion and deltamethrin, and the larvicide temephos. The lethal concentrations were obtained for field-collected specimens and compared to the susceptible reference strain ROCK, MRA-734. Mosquitoes from all the localities showed resistance to deltamethrin and susceptibility to malathion. On the other hand, mosquitoes demonstrated resistance to the larvicide temephos in 5 of the 14 localities analyzed. The results obtained in this research may be used by healthcare decision-makers to improve vector control in Ecuador. Rotation of insecticides and alternative biological vector control strategies should be considered to manage the resistance observed in Ae. aegypti to deltamethrin and temephos. New strategies to use insecticides should also be aimed to prevent selective pressure with malathion.

Hierarchical Virtual Screening of Potential Insectides Inhibitors of Acetylcholinesterase and Juvenile Hormone from Temephos

Aedes aegypti (Linnaeus, 1762; Diptera: Culicidae) is the main vector transmitting viral diseases such as dengue fever, dengue haemorrhagic fever, urban yellow fever, zika and chikungunya. Worldwide, especially in the Americas and Brazil, many cases of dengue have been reported in recent years, which have shown significant growth. The main control strategy is the elimination of the vector, carried out through various education programs, to change human habits, but the most usual is biological control, together with environmental management and chemical control. The most commonly insecticide used is temephos (an organophosphorus compound), but Aedes aegypti populations have shown resistance and the product is highly toxic, so we chose it as a template molecule to perform a ligand-based virtual screening in the ChemBrigde (DIVERSet-CL subcollection) database, searching for derivatives with similarity in shape (ROCS) and electrostatic potential (EON). Thus, fourty-five molecules were filtered based on their pharmacokinetic and toxicological properties and 11 molecules were selected by a molecular docking study, including binding affinity and mode of interaction. The L46, L66 and L68 molecules show potential inhibitory activity for both the insect (−9.28, −10.08 and −6.78 Kcal/mol, respectively) and human (−6.05, 6.25 and 7.2 Kcal/mol respectively) enzymes, as well as the juvenile hormone protein (−9.2; −10.96 and −8.16 kcal/mol, respectively), showing a significant difference in comparison to the template molecule temephos. Molecules L46, L66 and L68 interacted with important amino acids at each catalytic site of the enzyme reported in the literature. Thus, the molecules here investigated are potential inhibitors for both the acetylcholinesterase enzymes and juvenile hormone protein–from insect and humans, characterizing them as a potential insecticide against the Aedes aegypti mosquito.

Effects of prenatal exposure to temephos on behavior and social interaction

The neurodevelopment period is susceptible to alterations by genetic and environmental factors, such as the exposure to organophosphates (OP). The OP is neurotoxic and has been associated with neurological diseases pathophysiology. The OP temephos is widely used against Aedes aegypti in Brazil's public health programs.

PURPOSE

To evaluate behavioral effects of prenatal exposition to temephos in Wistar rats.

METHODS

First, we divided pregnant females into groups: those who received temephos diluted in distilled water by gavage between gestational days 6-13 and those who received only distilled water in the same period and volume. Then, we divided pups according to sex and exposure, and we made the behavioral tests on postnatal day 30.

RESULTS

Prenatal exposure to temephos caused hyperactivity, stereotyped behavior, and social impairment in animals.

CONCLUSION

These results are similar to the altered behavior presented in some neurobiological diseases models, like Attention Deficit Hyperactivity Disorder and Autism Spectrum Disorders, and this study may bring a red alert to the large use of temephos in Brazil, due to the damage caused by its exposure.

Insecticide susceptibility status of invasive Aedes albopictus across dengue endemic districts of Odisha, India

BACKGROUND

Aedes albopictus is currently the most invasive mosquito species in the world. Keeping in view the wide emergence of insecticide resistance, it is imperative to focus on the current susceptibility status for various insecticides in Ae. albopictus. This study focused on understanding the insecticide resistance mechanism of Ae. albopictus collected from dengue-endemic districts of Odisha.

RESULTS

Insecticide resistance was evaluated by using standardized bioassay kits (WHO) and biochemical analysis. Larval bioassays revealed the highest level of resistance from Jaipur (JP) population with a RR₅₀ of 15.3 and LC₅₀ of 1.177 ppm compared with an LC₅₀ of 0.077 for the susceptible strain LabS. Results indicated the presence of dichlorodiphenyltrichloroethane resistance in the majority of adult populations. Elevated activity of nonspecific esterases and cytochrome P450s MFO indicated probable resistance to organophosphates and pyrethroids. Molecular screening for common insecticide target-site mutations confirmed the absence of the 'knockdown resistance' response for pyrethroid insecticide in Ae. albopictus population, suggesting its continual effectiveness as the major insecticide of significant importance in future vector-control programmes.

CONCLUSION

This is the first report of a kdr mutation in Ae. albopictus in India and highlights the need for intensive research on other unexplored target-site mutations that might also contribute to pyrethroid resistance. Effective management and sustainable use of insecticides can be implemented by understanding resistance mechanisms and development of appropriate diagnostic tools. © 2017 Society of Chemical Industry.

Larval Age and Nutrition Affect the Susceptibility of Culex quinquefasciatus (Diptera: Culicidae) to Temephos

Larval age and nutrition significantly affected the insect's physiology. These influences are important when rearing a population of vectors that is used to monitor the resistance level, in which standardized conditions are crucial for a more harmonized result. Little information has been reported on the effects of larval age and nutrition on the susceptibility of insects to insecticides, and therefore, we studied the effects on the susceptibility of Culex quinquefasciatus Say's (Diptera: Culicidae) larvae to temephos by comparing the median lethal concentration (LC50) after 24 hr between the second and fourth instar larvae and between the larvae that fed on protein-based and carbohydrate-based larval diets. The susceptibility of the larvae was significantly affected by the larval diets, as the larvae that fed on protein-based beef food and milk food demonstrated significantly higher LC50 value compared with the larvae that fed on carbohydrate-based food: lab food and yeast food. The larval diet interacted significantly with the larval age: while the second instar larvae were susceptible to temephos when supplied with carbohydrate-based food, the second and fourth instar larvae had no significant effect when supplied with protein-based diets, implying that a protein-rich environment may cause the mosquito to be less susceptible to temephos. This study suggested the importance of standardizing nutrition when rearing a vector population in order to obtain more harmonized dosage-response results in an insecticide resistance monitoring program. Future research could focus on the biochemical mechanism between the nutrition and the enzymatic activities of the vector.

Synergistic effect of entomopathogenic fungus Fusarium oxysporum extract in combination with temephos against three major mosquito vectors

Mosquito control using chemical insecticides is facing a major challenge due to development of insecticide resistance. Improving the efficiency of existing insecticides using synergistic secondary metabolites of biological origin is increasingly being researched. Herein, we evaluated the toxicity of Fusarium oxysporum extract alone and in binary combinations with temephos, on larvae and pupae of Anopheles stephensi, Aedes aegypti and Culex quinquefaciatus. F. oxysporum extract was characterized using TLC, FT-IR and GC-MS. After 24 h of exposure, the binary combination of temephos + F. oxysporum extract (1:1 ratio) was highly toxic to larvae of An. stephensi (LC50: 35.927 μg/ml), Ae. aegypti (LC50: 20.763 μg/ml) and Cx. quinquefasciatus, (LC50: 51.199 μg/ml). For pupae LC50 values were 38.668, 26.394, and 72.086 μg/ml, respectively. Histology studies of mosquitoes exposed to F. oxysporum extract showed vacuolation in epithelium, as well as in adipose, and muscle tissues of larval midgut. Overall, our results show that the synergistic combination of temephos and F. oxysporum extract is highly effective to control mosquito young instars.

Revised Discriminating Lethal Doses For Resistance Monitoring Program on Aedes albopictus Against Temephos and Malathion in Penang Island, Malaysia

Dengue vector control still heavily relies on the use of chemical insecticides, and the widespread use of insecticides has led to resistance in mosquitoes. The diagnostic dose is a key part of resistance monitoring. The present study corroborates the discriminating lethal doses of temephos and malathion based on dose-response of known susceptible strain of Aedes albopictus following the World Health Organization (WHO) diagnostic test procedure. Late 3rd and early 4th instars were tested with a range of larvicides to determine the lethal concentrations (LC₅₀ and LC₉₉) values. A slightly higher diagnostic dose of 0.020 mg/liter as compared with the WHO-established value of 0.012 mg/liter was observed for temephos. Meanwhile, a malathion diagnostic dose of 0.200 mg/liter is also reported here since there are no such reported values by WHO. Doubling the LC₉₉ values of susceptible strains, 3 of the 5 wild-collected populations showed resistance to temephos and 2 showed incipient resistance; all 5 populations showed incipient resistance to malathion. The revised and established lethal diagnostic dose findings from the current work are crucial to elaborate on the variation in susceptibility of Ae. albopictus in future resistance monitoring programs in Malaysia.

Susceptibility to Temephos and Spinosad in Aedes aegypti (Diptera: Culicidae) From Puerto Rico

We examined the susceptibility to temephos and spinosad (Natular EC) of eight Aedes aegypti (L.) populations from Puerto Rico, following WHO method (WHO 2005). Enzyme activity was measured for alpha- and beta-esterases, multiple function oxidases, glutathione-s-transferases, and insensitive acetylcholinesterase and was tested for correlation with the susceptibility level. The results showed that larval populations from Puerto Rico obtained during 2014 were found to be susceptible to both larvicides, with low (resistance factor) RRLC50 values (<5 fold) and altered and incipiently altered enzyme expression for all populations, except the insensitive acetylcholinesterase enzyme, where only the population of Ponce showed overexpression (53.3%) above the threshold established with the New Orleans susceptible strain. We recommend the use of both larvicides for mosquito control in the study area and encourage further susceptibility monitoring.

Differential protein expression in the midgut of Culex quinquefasciatus mosquitoes induced by the insecticide temephos

Mosquitoes are vectors for pathogens of malaria, lymphatic filariasis, dengue, chikungunya, yellow fever and Japanese encephalitis. Culex quinquefasciatus Say, 1823 (Diptera: Culicidae) is a known vector of lymphatic filariasis. Its control in Brazil has been managed using the organophosphate temephos. Studies examining the proteins of Cx. quinquefasciatus that are differentially expressed in response to temephos further understanding of the modes of action of the insecticide and may potentially identify resistance factors in the mosquito. In the present study, a comparative proteomic analysis, using 2-dimensional electrophoresis coupled with matrix-assisted laser desorption/ionization (MALDI) time of flight (TOF)/TOF mass spectrometry, and bioinformatics analyses were performed to identify midgut proteins in Cx. quinquefasciatus larvae that were differentially expressed in response to exposure to temephos relative to those in untreated controls. A total of 91 protein spots were differentially expressed; 40 were upregulated and 51 were downregulated by temephos. A total of 22 proteins, predominantly upregulated, were identified as known to play a role in the immune response, whereas the downregulated proteins were involved in energy and protein catabolism. This is the first proteome study of the midgut of Cx. quinquefasciatus and it provides insights into the molecular mechanisms of insecticide-induced responses in the mosquito.

Investigation of mosquito oviposition pheromone as lethal lure for the control of Aedes aegypti (L.) (Diptera: Culicidae)

BACKGROUND

The trend in chemical insecticide development has focused on improving the efficacy against mosquitoes while reducing the environmental impact. Lethal lures apply an "attract-and-kill" strategy that draws the insect to the killing agent rather than bringing the killing agent to the insect.

METHODS

In this study, the mosquito oviposition pheromone was extracted from the eggs of Aedes aegypti (L.) and further investigated with a combination of pheromone and granular temephos as a lethal lure.

RESULTS

The compound caproic acid attracted significantly more egg-laying mosquitos at 1 ppm (660.83 ± 91.61) than the control (343.83 ± 56.24), which consisted of solvent only (Oviposition Activity Index: 0.316). Further investigation of the combination of caproic acid with granular temephos as a lethal lure attracted significantly more gravid female Ae. aegypti to oviposit their eggs than the temephos treated water and control.

CONCLUSIONS

This indicated the ability of caproic acid in acting as an attractant and counters the repellency effect of temephos. Additionally, the presence of temephos in the lethal lure also restricted the hatching of the eggs and killed any larvae that hatched.

Susceptibility status of Aedes aegypti (L.) (Diptera: Culicidae) to temephos in Venezuela

BACKGROUND

Temephos is an insecticide widely used in Venezuela to control the proliferation of the larvae of Aedes aegypti (L.), the principal vector of dengue virus. The aim of this study was to identify the susceptibility to temephos of Ae. aegypti in four locations in western Venezuela: Lara, Tres Esquinas, Ureña and Pampanito. Larval bioassays were conducted on samples collected in 2008 and 2010, and the levels of α- and β-esterases, mixed-function oxidases, glutathione-S-transferase and insensitive acethyl cholinesterase were determined.

RESULTS

Larval populations from western Venezuela obtained during 2008 and 2010 were found to be susceptible to temephos, with low resistance ratios and without overexpression of enzymes.

CONCLUSIONS

The low RR values reveal the effectiveness of temephos in controlling the larval populations of Ae. aegypti. Control strategies must be vigorously monitored to maintain the susceptibility to temephos of these populations of Ae. aegypti.

Resistance Mechanisms of Anopheles stephensi (Diptera: Culicidae) to Temephos

BACKGROUND

Anopheles stephensi is a sub-tropical species and has been considered as one of the most important vector of human malaria throughout the Middle East and South Asian region including the malarious areas of southern Iran. Current reports confirmed An. stephensi resistance to temephos in Oman and India. However, there is no comprehensive research on mechanisms of temephos resistance in An. stephensi in the literature. This study was designed in order to clarify the enzymatic and molecular mechanisms of temephos resistance in this species.

METHODS

Profile activities of α- and ß-esterases, mixed function oxidase (MFO), glutathione-S-transferase (GST), insensitive acetylcholinesterase, and para-nitrophenyl acetate (PNPA)-esterase enzymes were tested for An. stephensi strain with resistance ratio of 15.82 to temephos in comparison with susceptible strain.

RESULTS

Results showed that the mean activity of α-EST, GST and AChE enzymes were classified as altered indicating metabolic mechanisms have considerable role in resistance of An. stephensi to temephos. Molecular study using PCR-RFLP method to trace the G119S mutation in ACE-1 gene showed lack of the mutation responsible for organophosphate insecticide resistance in the temephos-selected strain of An. stephensi.

CONCLUSION

This study showed that the altered enzymes but not targets site insensitivity of ACE-1 are responsible for temephos resistance in An. stephensi in south of Iran.

Silencing of P-glycoprotein increases mortality in temephos-treated Aedes aegypti larvae

Re-emergence of vector-borne diseases such as dengue and yellow fever, which are both transmitted by the Aedes aegypti mosquito, has been correlated with insecticide resistance. P-glycoproteins (P-gps) are ATP-dependent efflux pumps that are involved in the transport of substrates across membranes. Some of these proteins have been implicated in multidrug resistance (MDR). In this study, we identified a putative P-glycoprotein in the Ae. aegypti database based on its significantly high identity with Anopheles gambiae, Culex quinquefasciatus, Drosophila melanogaster and human P-gps. The basal ATPase activity of ATP-binding cassette transporters in larvae was significantly increased in the presence of MDR modulators (verapamil and quinidine). An eightfold increase in Ae. aegypti P-gp (AaegP-gp) gene expression was detected in temephos-treated larvae as determined by quantitative PCR. To analyse the potential role of AaegP-gp in insecticide efflux, a temephos larvicide assay was performed in the presence of verapamil. The results showed an increase of 24% in temephos toxicity, which is in agreement with the efflux reversing effect. RNA interference (RNAi)-mediated silencing of the AaegP-gp gene caused a significant increase in temephos toxicity (57%). In conclusion, we have demonstrated for the first time in insects that insecticide-induced P-gp expression can be involved in the modulation of insecticide efflux.

Patterns of Aedes aegypti (Diptera: Culicidae) infestation and container productivity measured using pupal and Stegomyia indices in northern Argentina

A citywide control program of Aedes aegypti (L.) (Diptera: Culicidae) mainly based on the use of larvicides reduced infestations but failed to achieve the desired target levels in Clorinda, northeastern Argentina, over 5 yr of interventions. To understand the underlying causes of persistent infestations and to develop new control tactics adapted to the local context, we conducted two pupal surveys in a large neighborhood with approximately 2,500 houses and recorded several variables for every container inspected in fall and spring 2007. In total, 4,076 lots and 4,267 containers were inspected over both surveys, and 8,391 Ae. aegypti pupae were collected. Large tanks used for potable water storage were the most abundant and the most productive type of container, accounting for 65-84% of all the pupae collected. Therefore, large tanks were key containers and candidates for improved targeted interventions. Multivariate analysis showed that containers located in the yard, at low sun exposure, unlidded, filled with rain water, and holding polluted water were all more likely to be infested by larvae or pupae. When only infested containers were considered, productivity of pupae was most closely associated with large tanks and rain water. A stochastic simulation model was developed to calculate the expected correlations between pupal and Stegomyia indices according to the characteristics of the distribution of larvae and pupae per container and the spatial scale at which the indices were computed. The correlation between pupal and Stegomyia indices is expected to increase as infestation levels decline.