Abstract
BackgroundThe yellow fever mosquito Aedes aegypti is essentially a container-inhabiting species that is closely associated with urban areas. This species is a vector of human pathogens, including dengue and yellow fever viruses, and its control is of paramount importance for disease prevention. Insecticide use against mosquito juvenile stages (i.e. larvae and pupae) is growing in importance, particularly due to the ever-growing problems of resistance to adult-targeted insecticides and human safety concerns regarding such use in human dwellings. However, insecticide effects on insects in general and mosquitoes in particular primarily focus on their lethal effects. Thus, sublethal effects of such compounds in mosquito juveniles may have important effects on their environmental prevalence. In this study, we assessed the survival and swimming behavior of A. aegypti 4th instar larvae (L4) and pupae exposed to increasing concentrations of insecticides. We also assessed cell death in the neuromuscular system of juveniles.MethodsThird instar larvae of A. aegypti were exposed to different concentrations of azadirachtin, deltamethrin, imidacloprid and spinosad. Insect survival was assessed for 10 days. The distance swam, the resting time and the time spent in slow swimming were assessed in 4th instar larvae (L4) and pupae. Muscular and nervous cells of L4 and pupae exposed to insecticides were marked with the TUNEL reaction. The results from the survival bioassays were subjected to survival analysis while the swimming behavioral data were subjected to analyses of covariance, complemented with a regression analysis.ResultsAll insecticides exhibited concentration-dependent effects on survival of larvae and pupae of the yellow fever mosquito. The pyrethroid deltamethrin was the most toxic insecticide followed by spinosad, imidacloprid, and azadirachtin, which exhibited low potency against the juveniles. All insecticides except azadirachtin reduced L4 swimming speed and wriggling movements. A similar trend was also observed for swimming pupa, except for imidacloprid, which increased the swimming activity of pupa. Curiously, the insecticides did not affect cell damage in the neuromuscular system of larvae and pupae.ConclusionsDeltamethrin and spinosad were the main compounds to exhibit lethal effects, which allowed the control of A. aegypti larvae and pupae, and impair their swimming potentially compromising foraging and predation likelihood.
Highlights
The yellow fever mosquito Aedes aegypti is essentially a container-inhabiting species that is closely associated with urban areas
Insecticide use against mosquito juveniles is growing in importance, but this use is potentially afflicted by the same shortcomings of insecticides that target adults and requires alternative compounds
In addition to the neonicotinoid imidacloprid, several other compounds have been tested against mosquitoes, including biopesticides, such as azadirachtin, a terpenoid mixture obtained from the neem tree
Summary
The yellow fever mosquito Aedes aegypti is essentially a container-inhabiting species that is closely associated with urban areas. This species is a vector of human pathogens, including dengue and yellow fever viruses, and its control is of paramount importance for disease prevention. Insecticide use against mosquito juvenile stages (i.e. larvae and pupae) is growing in importance, due to the ever-growing problems of resistance to adult-targeted insecticides and human safety concerns regarding such use in human dwellings. The yellow fever mosquito Aedes aegypti is a containerinhabiting species that is closely associated with urban areas This species is a vector of human pathogens, including dengue and yellow fever viruses. Juss.), and spinosad, a mixture of secondary metabolites obtained as fermentation products from the soil actinomycete Saccharopolyspora spinosa [8,9,10,11,12,13]
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