Increased biting rate and decreasedWolbachiadensity in irradiatedAedesmosquitoes

Abstract

Releasing considerable numbers of radiation-sterilized males is a promising strategy to suppress mosquito vectors. However, under large-scale settings, small percentages of biting females can also be released in the field. Currently, the effects of the irradiation on host-seeking and host-biting behaviors have not been exhaustively investigated. Information is also lacking regarding the effects of a sterilizing treatment on the endosymbiotic bacterium Wolbachia , that is known to attenuate the vector competence of infected mosquito species. To ascertain the risks associated with the release of irradiated females, the pupae of two Aedes albopictus strains, differing by their natural or artificial Wolbachia infection type, were X-ray-treated using various doses to monitor key fitness parameters and biting behavior over two weeks. The effect of the radiation on Wolbachia was investigated by qPCR and FISH analysis. Radiation doses of 35 and 45 Gy completely inhibited progeny production but did not significantly affect Ae. albopictus female survival and flight ability, and caused a tripling of the number of bites per female per week compared to untreated controls. These results were also confirmed in Ae. aegypti after treatment at 5 0 Gy. A partial Ae. albopictus female sterility was achieved at 28 Gy but the number of weekly bites more than doubled compared to the controls. The Wolbachia density showed a significant downward trend in 45-Gy-irradiated females and decreased with adult aging and in younger treated pupae. This trend was confirmed in ovaries but not in extraovaric tissues. FISH analysis evidenced a strongly reduced Wolbachia -specific fluorescence in the ovaries of 13±1-day-old females. These findings suggested that irradiation could markedly increase the vectorial capacity of female mosquitoes, raising concerns about open field programs involving the release of substantial numbers of irradiated mosquitoes in the absence of perfect sexing methods.