Assessment of radiation-induced sterility, longevity, and reproductive characteristics of the Aedes aegypti (Diptera: Culicidae) strain of Swat: A step towards the implementation of SIT in Pakistan.

BACKGROUND OBJECTIVES:Biological approaches for vector mosquito control such as sterile insect technique (SIT) requires sterilization of male mosquitoes through specific radiation doses for sterility induction in males. Under the SIT program, the males used must be compatible with the wild males in vigor, flight and selection of mate. Much of this potential is determined by the diet provided in the larval stages and optimizing the irradiation doses that cause complete sterility but have very minimal effect on the lives of irradiated males. The current study is designed to evaluate gamma radiation doses for inducing sterility in male Aedes aegypti mosquitoes with a genomic background from Pakistan (Swat district) and to assess the effects of radiation exposure on the competency of irradiated males and other life traits of irradiated mosquitoes. METHODS:Sterilization of 17-hour-old male pupae (groups of 50 pupa/cup in three replicates) of the Ae. aegypti Swat strain was conducted using radiation doses of 30, 60, 70, 90, and 105 gray (Gy) from (Co60) at the Nuclear Institute for Food and Agriculture (NIFA) in Peshawar, Pakistan. Post-irradiated pupae were released in adult cages. Virgin females of the same cohort were released (1:1) to mate with the irradiated males. Mortality, longevity, mating competitiveness of males, and female fecundity were recorded. RESULTS:An average of 71 eggs per female was recorded in control with 86% hatch rate. Individual females mated with a 60 Gy treated males produced 60 ± 0.6 eggs per female with 17% hatch rate, and those mated with 70 Gy males produced 42 ± 0.01 eggs with a nil hatch rate, whereas females mated with males treated with ≥70 Gy doses did not reproduce to next generation. Females in groups of 50 mated with 60, 70 Gy treated males (equal pairs), produced 369±1.3 and 98±0.01 eggs with 15% and zero hatch rate. Significant dose dependent reduction in longevity was observed for >30 Gy doses. The matting competence of irradiated males was about half that of un-irradiated males. INTERPRETATION CONCLUSION:Aedes aegypti with a Pakistani genomic background treated with a ≥70 Gy dose of gamma radiation induced complete sterility in males and provided the first- step foundation for SIT application in Pakistan. Further extensive studies are required to optimize the SIT techniques so that fully sterile males with very minor quality changes can be produced on large scales for field trials.