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Background: The continued use of chemical insecticides in the context of the National Program of Dengue Control in Brazil has generated a high selective pressure on the natural populations of Aedes aegypti, leading to their resistance to these compounds in the field. Fitness costs have been described as adaptive consequences of resistance. This study evaluated the biological and reproductive performance of A. aegypti strains and a field population resistant to temephos, the main larvicide used for controlling mosquitoes. Methods: Comparative tests were performed with a resistant field population from the municipality of Arcoverde, Pernambuco State, Brazil, with a high rate of temephos resistance (RR = 226.6) and three isogenetic laboratory strains from the same origin (Araripina municipality, Pernambuco): RecR (RR = 283.6); RecRNEx (RR = 250.5), a strain under a process of resistance reversion; and RecRev (RR = 2.32), a reversed susceptible strain used as an experimental control. Results: Our study revealed that the absence of selective pressure imposed by exposure to temephos, for five consecutive generations, led to a discrete reduction of the resistance ratio and the response of the detoxifying enzymes. Most of the 19 biological parameters were impaired in the resistant strains and field population. The analysis of the fertility life table confirmed the presence of reproductive disadvantages for the resistant individuals. Similarly, the longevity, body size, and total energetic resources were also lower for the resistant females, except for the last two parameters in the field females (Arcoverde). In contrast, the sex ratio and embryonic viability suffered no interference in all strains or population evaluated, regardless of their status of resistance to temephos. Conclusions: The reproductive potential and survival of the resistant individuals were compromised. The parameters most affected were the larval development time, fecundity, net reproduction rate, and the generational doubling time. These fitness costs in the natural population and laboratory strains investigated are likely associated with maintaining the metabolic mechanism of resistance to temephos. Our results show that despite these costs, the highly temephos resistant populations can compensate for these losses and successfully overcome the control actions that are based on the use of chemical insecticides. [ABSTRACT FROM AUTHOR]

Resistance to chemical insecticides detected in Aedes aegypti (L.) mosquitoes has been a problem for the National Dengue Control Program (PNCD) over the last years. In order to provide deeper knowledge of resistance to xenobiotics, our study evaluated the susceptibility profile of temephos, diflubenzuron, and cypermethrin insecticides in natural mosquito populations from the Pernambuco State, associating these results with the local historical use of such compounds. Furthermore, mechanisms that may be associated with this particular type of resistance were characterized. Bioassays with multiple temephos and diflubenzuron concentrations were performed to detect and quantify resistance. For cypermethrin, diagnostic dose assays were performed. Biochemical tests were carried out to quantify the activity of detoxification enzymes. In addition, a screening of mutations present in the voltage-gated sodium channel gene (NaV) was performed in samples previously submitted to bioassays with cypermethrin. The populations under study were resistant to temephos and showed a positive correlation between insecticide consumption and the resistance ratio (RR) to the compound. For diflubenzuron, the biological activity ratio (BAR) ranged from 1.3 to 4.7 times, when compared to the susceptible strain. All populations showed resistance to cypermethrin. Altered enzymatic profiles of alpha, p -nitrophenyl acetate (PNPA) esterases and glutathione-S-transferases were recorded in most of these samples. Molecular analysis demonstrated that Arcoverde was the only population that presented the mutated form 1016Ile/Ile. These findings show that the situation is critical vis-à-vis the effectiveness of mosquito control using chemical insecticides, since resistance to temephos and cypermethrin is widespread in Ae. aegypti from Pernambuco. [ABSTRACT FROM AUTHOR]

The glutathione S-transferases (GSTs) are enzymes involved in several distinct biological processes. In insects, the GSTs, especially delta and epsilon classes, play a key role in the metabolism of xenobiotics used to control insect populations. Here, we investigated its potential role in temephos resistance, examining the GSTE2 gene from susceptible (RecL) and resistant (RecR) strains of the mosquito Aedes aegypti, vector for several pathogenic arboviruses. Total GST enzymatic activity and the GSTE2 gene expression profile were evaluated, with the GSTE2 cDNA and genomic loci sequenced from both strains. Recombinant GSTE2 and mutants were produced in a heterologous expression system and assayed for enzyme kinetic parameters. These proteins also had their 3D structure predicted through molecular modeling. Our results showed that RecR has a profile of total GST enzymatic activity higher than RecL, with the expression of the GSTE2 gene in resistant larvae increasing six folds. Four exclusive RecR mutations were observed (L111S, I150V, E178A and A198E), which were absent in the laboratory susceptible strains. The enzymatic activity of the recombinant GSTE2 showed different kinetic parameters, with the GSTE2 RecR showing an enhanced ability to metabolize its substrate. The I150V mutation was shown to induce significant changes in catalytic parameters and a 3D modeling of GSTE2 mapped two of the RecR changes (L111S and I150V) near the enzyme's catalytic pocket, also implying an impact on its catalytic activity. Our results reinforce a potential role for GSTE2 in the metabolic resistance phenotype while contributing to the understanding of the molecular basis for the resistance mechanism., Competing Interests: Declaration of Competing Interest Authors declare that they have no competing interests, (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)