Alternative insecticides for larval control of the dengue vector Aedes aegypti in Lao PDR: insecticide resistance and semi-field trial study.

Background: The mosquito Aedes aegypti is the primary vector of several arboviruses, such as dengue, chikungunya and Zika, and represents a major public health problem in Southeast Asia. In Laos, where dengue is reemerging, several Ae. aegypti populations from the capital Vientiane have shown resistance to the organophosphate temephos, a commonly-used larvicide for public health interventions.

Methods: Here, we tested the insecticide susceptibility of a wild larval population of Ae. aegypti against Bacillus thuringiensis israelensis (Bti), diflubenzuron, pyriproxyfen and spinosad. Residual efficacies of Bti (VectobacWG®), diflubenzuron (Killmos®) and temephos (Abate®) were then evaluated under simulated field conditions against the wild Ae. aegypti population.

Results: The larval bioassays showed that the wild Ae. aegypti strain was moderately resistant to temephos and spinosad (resistance ratio, RR < 5) and fully susceptible to the other insecticides (RR = 1). The simulated field trial bioassays showed that all of the insecticides tested remained above the WHO acceptable larvicide threshold after 28 weeks.

Conclusions: These results suggest that Bti and diflubenzuron may be promising alternative larvicides for controlling dengue vectors in water-storage containers in Laos, especially against Ae. aegypti populations, in which resistance to temephos has been detected.