Impact of the insect growth regulator pyriproxyfen on life table characteristics of Aedes albopictus

Abstract

Aedes albopictus is a vector of several arboviruses, including dengue, chikungunya, and Zika. However, control of this day-active species is difficult with ultra-low volume treatments applied at dusk/dawn periods. Consequently, the impacts of an alternative method (residual barrier spray) used to control resting mosquito adults were evaluated. Eggs were collected from field study sites treated with Demand CS[registered] (pyrethroid adulticide) (active ingredient [AI]: lambda-cyhalothrin) plus Archer[registered] (insect growth regulator larvicide) (AI: pyriproxyfen) at pre-determined concentrations and life table characteristics assessed in the laboratory. In a separate laboratory study, blood fed Ae. albopictus were exposed to Archer[registered] residue in glass bottles (to approximate contact from a barrier spray) and subsequently allowed to oviposit. Control mosquitoes were exposed to clean bottles. Mosquitoes were held in incubators at 28[degrees]C for the duration of the experiments. To evaluate potential dilution effects of water volume, mosquitoes were allowed to oviposit in (relatively) small (59 mL water) or large (177 mL water) containers. We characterized the extent to which fecundity (number of eggs laid), fertility rate (number of larvae hatched/number of eggs laid*100), and emergence rate (number of adults emerged/number of larvae hatched*100) differed between groups. In the control group, 18-21 (82-95%) mosquitoes laid eggs, while only 10-11 (45-50%) mosquitoes laid eggs in the group exposed to pyriproxyfen. Significantly lower (P=0.0008) fecundity was observed in mosquitoes exposed to pyriproxyfen (mean[plus-minus]SE) (small container: 25.2[plus-minus]7.1, large container: 24.3[plus-minus]7.1) compared to control mosquitoes (small container: 49.2[plus-minus]7.8, large container: 52.7[plus-minus]5.2). Regardless of treatment, no significant differences in fecundity were observed between mosquitoes allowed to oviposit in different sized containers. Hatch rate was significantly lower in the pyriproxyfen group and was impacted by size of container (P=0.032) and treatment (P< 0.0001) (large, control: 61.9% [plus-minus] 7.8; small, control: 38.0% [plus-minus] 7.1; large, treated: 10.3% [plus-minus] 2.4; small, treated: 2.9% [plus-minus] 1.9). Adult emergence rates were not significantly impacted by treatment or size of container. Pyriproxyfen applied as a barrier spray may be an effective tool for controlling Ae. albopictus and other peridomestic mosquitoes.