Spinosad, a Naturally Derived Insecticide, for Control of Aedes aegypti (Diptera: Culicidae): Efficacy, Persistence, and Elicited Oviposition Response

The naturally derived insecticide spinosad is a reduced-risk material that is neurotoxic to Diptera. The 24-h 50% lethal concentration by laboratory bioassay in third instars of Aedes aegypti (L.) (Diptera: Culicidae) (Rockefeller strain) was estimated at 0.026 ppm. Two identical field trials were performed in an urban cemetery in southern Mexico during the dry and wet seasons. Water containers treated with 1 or 5 ppm spinosad suspension concentrate (Tracer, Dow Agrosciences) were as effective in preventing the development of Aedes spp. (mostly Ae. aegypti) as temephos granules during both trials, whereas the bacterial insecticide VectoBac 12AS performed poorly. The half-life of aqueous solutions of spinosad (10 ppm) placed in a warm sunny location was 2.1 d, compared with 24.5 d for solutions in a shaded location. Spinosad, temephos, and VectoBac were not repellent to gravid Ae. aegypti at the concentrations tested, and no ovicidal properties were observed. The 24-h survival of neonate larvae but was reduced by 94-100% in the presence of residues carried over from the spinosad treatments, but it was not affected by residues of temephos or VectoBac. The toxicological properties of spinosad, combined with its favorable environmental profile, should encourage the detailed evaluation of spinosad as a mosquito larvicide in domestic and urban environments.