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.

Fitness Cost of Sequential Selection with Deltamethrin in Aedes aegypti (Diptera: Culicidae).

In Mexico, Aedes aegypti (L.) is the primary dengue vector, chikungunya, and Zika viruses. The continued use of synthetic pyrethroids has led to the development of resistance in target populations, which has diminished the effectiveness of vector control programs. Resistance has been associated with disadvantages that affect the biological parameters of resistant mosquitoes compared to susceptible ones. In the present study, the disadvantages were evaluated by parameters related to survival and reproduction ('fitness cost') after selection with deltamethrin for five generations. The parameters analyzed were the length of the development cycle, sex ratio, survival, longevity, fecundity, egg viability, preoviposition, oviposition and postoviposition periods, and growth parameters. In the deltamethrin-selected strain, there was a decrease in the development cycle duration, the percentage of pupae, the oviposition period, and eggs viability. Although mean daily fecundity was not affected after the selection process, this, together with the decrease in the survival and fecundity levels by specific age, significantly affected the gross reproductive rate (GRR), net reproductive rate (Ro), and intrinsic growth rate (rm) of the group selected for five generations with deltamethrin compared to the group without selection. Identifying the 'cost' of resistance in biological fitness represents an advantage if it is desired to limit the spread of resistant populations since the fitness cost is the less likely that resistant individuals will spread in the population. This represents an important factor to consider in designing integrated vector management programs.

Distribution and Frequency of the kdr Mutation V410L in Natural Populations of Aedes aegypti (L.) (Diptera: Culicidae) From Eastern and Southern Mexico.

Aedes aegypti (L.) is the primary vector of the viruses that cause dengue, Zika, and chikungunya, for which effective vaccines and drugs are still lacking. Current strategies for suppressing arbovirus outbreaks based on insecticide use pose a challenge because of the rapid increase in resistance. The widespread and excessive use of pyrethroid-based insecticides has created a large selection pressure for a kdr-type resistance, caused by mutations in the para gene of the voltage-gated sodium channel (vgsc). Our objective was to evaluate the allelic frequency of natural populations of Ae. aegypti of Mexico at codon 410 of the para gene. Twenty-six Ae. aegypti populations from east and southern Mexico were genotyped for the codon 410 using allele-specific PCR. The frequencies of the L410 allele in Ae. aegypti ranged from 0.10 to 0.99; however, most of the frequencies were in the range of 0.36 to 0.64. The highest frequencies were found in three populations from the state of Veracruz, namely, Minatitlan with 0.99, Poza Rica with 0.82, and Jose Cardel with 0.97, along with populations from Cancun in Quintana Roo with 0.93, Frontera in Tabasco with 0.91, and Ciudad del Carmen in Campeche with 0.86. The frequency of the L410 allele was high in all populations of Ae. aegypti with higher values in populations of the southeast of the country. The knowledge of specific substitutions in vgsc and their interaction to confer resistance is essential to predict and develop future strategies for resistance management in Ae. aegypti in Mexico.

Frequency and intensity of pyrethroid resistance through the CDC bottle bioassay and their association with the frequency of kdr mutations in Aedes aegypti (Diptera: Culicidae) from Mexico.

BACKGROUND: The control of Aedes aegypti (L.), the main urban vector that causes arboviral diseases such as dengue, Chikungunya and Zika, has proved to be a challenge because of a rapid increase in insecticide resistance. Therefore, adequate monitoring of insecticide resistance is an essential element in the control of Ae. aegypti and the diseases it transmits. We estimated the frequency and intensity (Resistance Frequency Rapid Diagnostic Test [F-RDT] and Resistance Intensity Rapid Diagnostic Test [I-RDT]) of pyrethroid resistance in populations of Ae. aegypti from Mexico using the bottle bioassay and results were related to the frequencies of knockdown resistance (kdr) mutations V1016I and F1534C. RESULTS: All populations under study were resistant to the pyrethroids: bifenthrin (99%), d-(cis-trans)-phenothrin (6.3% cis, 91.7% trans) and permethrin (99.5%) according to F-RDT, and showed moderate to high-intensity resistance at 10× the diagnostic dose (DD) in I-RDT. Frequencies of the kdr mutation V1016I in Ae. aegypti populations were correlated with moderate permethrin resistance at 10× DD, whereas F1534C mutation frequencies were correlated with high bifenthrin resistance at 5× DD. Both I1016 and C1535 were highly correlated with high-intensity phenothrin resistance at 1× to 10× DD. CONCLUSIONS: This study showed that high frequencies of kdr mutations V1016I and F1534C are reflected in the results of F-RDT and I-RDT tests. Bioassays in conjunction with the characterization of genetic resistance mechanisms are indispensable in the strategic and rational management of resistance in mosquitoes. © 2018 Society of Chemical Industry.

Assessing the effect of selection with deltamethrin on biological parameters and detoxifying enzymes in Aedes aegypti (L.).

BACKGROUND: Resistance to insecticides through one or several mechanisms has a cost for an insect in various parameters of its biological cycle. The present study evaluated the effect of deltamethrin on detoxifying enzymes and biological parameters in a population of Aedes aegypti selected for 15 generations. The enzyme activities of alpha- and beta-esterases, mixed-function oxidases and glutathione-S-transferases were determined during selection, along with biological parameters. RESULTS: Overexpression of mixed-function oxidases as a mechanism of metabolic resistance to deltamethrin was found. There were decreases in percentages of eggs hatching, pupation and age-specific survival and in total survival at the end of the selection (F16 ). Although age-specific fecundity was not affected by selection with deltamethrin, total fertility, together with lower survival, significantly affected gross reproduction rate, gradually decreasing due to deltamethrin selection. Similarly, net reproductive rate and intrinsic growth rate were affected by selection. CONCLUSION: Alterations in life parameters could be due to the accumulation of noxious effects or deleterious genes related to detoxifying enzymes, specifically those coding for mixed-function oxidases, along with the presence of recessive alleles of the V1016I and F1534C mutations, associating deltamethrin resistance with fitness cost in Ae. aegypti. © 2017 Society of Chemical Industry.