Deltamethrin-mediated survival, behavior, and oenocyte morphology of insecticide-susceptible and resistant yellow fever mosquitos (Aedes aegypti)

Abstract

Insecticide use is the prevailing control tactic for the mosquito Aedes aegypti, a vector of several human viruses, which leads to ever-increasing problems of insecticide resistance in populations of this insect pest species. The underlying mechanisms of insecticide resistance may be linked to the metabolism of insecticides by various cells, including oenocytes. Oenocytes are ectodermal cells responsible for lipid metabolism and detoxification. The goal of this study was to evaluate the sublethal effects of deltamethrin on survival, behavior, and oenocyte structure in the immature mosquitoes of insecticide-susceptible and resistant strains of A. aegypti. Fourth instar larvae (L4) of both strains were exposed to different concentrations of deltamethrin (i.e., 0.001, 0.003, 0.005, and 0.007 ppm). After exposure, L4 were subjected to behavioral bioassays. Insecticide effects on cell integrity after deltamethrin exposure (at 0.003 or 0.005 ppm) were assessed by processing pupal oenocytes for transmission electron microscopy or TUNEL reaction. The insecticide resistant L4 survived all the tested concentrations, whereas the 0.007-ppm deltamethrin concentration had lethal effects on susceptible L4. Susceptible L4 were lethargic and exhibited less swimming activity than unexposed larvae, whereas the resistant L4 were hyperexcited following exposure to 0.005 ppm deltamethrin. No sublethal effects and no significant cell death were observed in the oenocytes of either susceptible or resistant insects exposed to deltamethrin. The present study illustrated the different responses of susceptible and resistant strains of A. aegypti following exposure to sublethal concentration of deltamethrin, and demonstrated how the behavior of the immature stage of the two strains varied, as well as oenocyte structure following insecticide exposure.

Deltamethrin toxicity and impaired swimming behavior of two backswimmer species

“…However, based on our results for deltamethrin toxicity, such conclusions should be analyzed with caution. Whereas the susceptibility of B. tarsalis to deltamethrin (LC50 ¼ 4.0 ng a.i./L) was similar to that of other backswimmer species (e.g., Anisops sardeu) in the subfamily Anisopinae [30], the deltamethrin LC50 for M. bentoi was several fold higher than that for B. tarsalis and A. sardeu, which reinforces the idea that differences in the toxicodynamics of insecticide poisoning, or in physiological and biochemical peculiarities associated with each aquatic insect species, regulate the susceptibilities of these organisms to insecticide exposure [1,4,14,15,26].…”

“…The susceptibility of aquatic insects to insecticides is related to physiological and behavioral constraints associated with aquatic ecosystems [1,15,20,26,27]. In the present study we demonstrated that 2 phylogenetically related backswimmer species (B. tarsalis and M. bentoi) had different susceptibilities to deltamethrin, which also had effects on individual swimming activities.…”

“…A common deltamethrin‐mediated behavioral impairment in arthropods is a decrease in locomotor activity , with consequent severe reductions in feeding and antipredator activities that lead to changes in survival (avoiding predators) or reproductive success . In the present study, short‐term exposure to deltamethrin was sufficient to alter individual (but not group) swimming activities (e.g., natural pattern of occupancy in the water column and resting time) in B. tarsalis , but not in M. bentoi .…”

“…These abilities are absent or are less effective in M. bentoi, which periodically has to renew the air carried in the plastron [40], thus helping to explain the longer periods spent in the most superficial depths of the water column. A common deltamethrin-mediated behavioral impairment in arthropods is a decrease in locomotor activity [26,27], with consequent severe reductions in feeding and antipredator activities [17,20] that lead to changes in survival (avoiding predators) or reproductive success [41]. In the present study, short-term exposure to deltamethrin was sufficient to alter individual (but not group) swimming activities (e.g., natural pattern of occupancy in the water column and resting time) in B. tarsalis, but not in M. bentoi.…”

Alternative control of Aedes aegypti resistant to pyrethroids: lethal and sublethal effects of monoterpene bioinsecticides

“…Populations were reared following the procedure described in Marriel et al . (2016) . The larvae of A. aegypti populations were kept in plastic trails (6 L) with 5 L of water (chlorine free) and they were fed with animal rations.…”