Investigações sobre os mecanismos de resistência em larvas e adultos de Aedes aegypti, Linnaeus, 1762

The use of neurotoxic insecticides against the mosquito Aedes aegypti is still an important component in dengue control programs. In Brazil, organophosphates (OP) and pyrethroids (PI) are used for the control of A. aegypti larvae and adults since, respectively, 1967 and 2000. The frequent use of these products has selected resistant vector populations, and prompted the Ministry of Health (MS) to start the coordination, in 1999, of an Aedes aegypti insecticide resistance monitoring network (MoReNAa); our laboratory participates in the network since its beginning. Resistance is mainly derived from metabolic factors (enzymes detoxifying the insecticides) or from mutations at the target sites of insecticides (in the Central Nervous System). Bioassays with larvae disclosed resistance of various populations to the OP temephos, larvicide employed for over 40 years in the country. MoReNAa network also performs bioassays with adults, molecular tests to assess substitution at the PI target site, the voltage regulated sodium channel (AaNAv), and biochemical assays that quantify, in adult mosquitoes, the activity of Glutathione S-Transferases (GST), Esterases and Mixed Function Oxidases (MFO) (related to metabolic resistance), and of Acetylcholinesterase (Ace) (target of OP and carbamates - CB). Besides using different insecticide classes against larvae and adults, the treatment are performed differently: in 4-6 times per year for larvae and only in emergency situations in the case of adult mosquitoes – a procedure that has the potential to elicit different mechanisms (and intensities) of resistance. Furthermore, bioassays for quantification of resistance to OP are made with larvae, while biochemical assays were available only for adult mosquitoes. These were the main reasons to adapt, in the context of this dissertation, biochemical assays for the larval stage of the vector. Considering the Ace test, consisting of two reactions, in the presence or in the absence of the CB propoxur, we identified - through the use of inhibition curves - differences between larvae and adults. We also detected, in some OP resistant vector populations, changes in the total activity of this enzyme. Since some of the enzymes of metabolic resistance are also involved in endogenous processes, that occur naturally in insects, we quantified their activity during the development of the reference strain of susceptibility, Rockefeller, and of two field populations. In these experiments we observed four major "categories " of enzyme activity profiles: 1) higher activity in the adult stage (AChE); 2) higher activity in the larval stage (“α-EST” and “β- EST” Esterases); 3) activities that increase during each stage evaluated (MFO) and 4) activities tending to increase in the end of the larval stage and to decrease in the first days of adult life (DVA) (Esterase “ρNPA” and GST). Subsequently, biochemical assays with larvae and adults of field populations revealed main changes in Ace and Esterases in the larval stage, GST changes preferably in the adult stage, and MFO alterations on both vector stages. These assays enable the detailed knowledge of resistance mechanisms of different vector populations and can contribute to define rational strategies for A. aegypti control.