Avaliação de infoquímicos presentes em ovos e larvas de Aedes (Stegomyia) aegypti (Linnaeus, 1762) (Diptera: Culicidae) como atraentes e/ou estimulantes de oviposição para grávidas co-específicas

Abstract

The choice of a suitable breeding site by Aedes (Stegomyia) aegypti is influenced by visual, physical and chemical stimuli. We aimed to evaluate the influence of chemical stimuli (infochemicals) present in waters inhabited by immature conspecifics that, once identified, have a potential use in A. aegypti gravid traps. The objectives of this study were to evaluate: (a) larval extracts of 3rd and 4th instars of A. aegypti as oviposition stimulants, (b) larval extracts of A. aegypti as oviposition attractant in the sticky trap MosquiTRAP, (c) A. aegypti eggs at different ages as oviposition stimulants, (d) the chemical profile of larval and eggs extracts. In the laboratory, tests were set up in cages (30×30×30 cm) where only one A. aegypti gravid female was evaluated in each test. We evaluated as oviposition stimulant extracts of (1) larval rearing water (LRW), (2) hexane extracts of larval rearing water (HLRW) and (3) methanol extracts of the body of larvae (MBL) at concentrations of 0.5, 2.0, 3.0 and 6.0 larvae/ml distilled water, and (4) 150 A. aegypti eggs at different ages (0, 2, 7, 15, 30, 90 and 180 days). In field experiments, MosquiTRAP® were baited with (1) tap water, (2) grass infusion of Panicum maximum (10%), (3) water and food pet pellet, (4) larval rearing water with pellet (8 larvae/ml), (5) larval rearing water without pellet and (6) larval rearing water without ration associated with infusion. Larval and eggs extracts were analyzed by gas chromatography and compared with standards synthetics oviposition stimulants or attractants (dodecanoic acid, tetradecanoic acid and n-heneicosane). The results showed that larval extract at concentration of 0.5 larvae/ml stimulated oviposition (Chi square, p > 0.05). Only eggs at 2, 7, 15 and 30 days old stimulated oviposition (p <0.05). We identified n-heneicosane in the body and larval rearing water extracts with hexane, while dodecanoic acid and tetradecanoic acid were found in methanol extracts of eggs. We observed many other compounds in larval and eggs extracts that were not identified. In the field, we observed that the mean number of A. aegypti female captured in traps containing LRW without pet food pellet was similar to that for the trap with grass infusion (Kruskal Wallis p > 0.05). The mixture of the extract of LRW with infusion did not significantly increase the capture (p> 0.05). We concluded that infochemicals produced by eggs and larvae interfere in oviposition of conspecifics, depending on the concentration of larvae and age of eggs.