235 - Optimization of irradiation sterility dose in Aedes aegypti for sterile insect technique (SIT) project in Orange County, California

Abstract: Invasive Aedes aegypti (L.) has steadily expanded its distribution throughout California, USA, during the past decade. A sterile insect technique (SIT) pilot project was developed at the Orange County Mosquito and Vector Control District (OCMVCD) to produce X-ray irradiated adult male Ae. aegypti as a suppression tool to reduce population density and the potential for local disease transmission. This study aims to determine the optimal irradiation dose for a local mosquito strain that minimizes negative fitness effects and maximizes sterility under lab and field conditions. X-ray doses of 0 (control), 40, 50, 60, and 70 Gy were applied to 5-7-day-old male adults, and then lab longevity was compared among groups at 14-, 21- and 30-day post treatment. Combined with males at 1:1 ratio, female mating status was examined by PCR with male-specific gene amplicon and blood feeding behavior by visual inspection. For each treatment dose, fecundity, egg hatch rate, male survivorship and mating competitiveness were compared. This was done using three replicates of 20 singly isolated female adults caged under two conditions, with irradiated males or with both irradiated and non-irradiated males. A total of 600 bloodfed and potentially mated females were selected. We found no significant effects of radiation dose on mating rate, survivorship, female blood-feeding success or fecundity, with results comparable to those observed in the control group of non-irradiated males. Compared to the control group, a 40 Gy dose reduced egg hatch rates by 98.7%, 50 Gy by 99.3%, 60 Gy by 99.7%, and at 70 Gy, no eggs hatched. Male mating competitiveness measured by the Fried index was similar for mosquitoes radiated at 50 Gy and above. Ongoing dose-response studies using single point and multipoint mark-release-recapture (MRR) field trials will further validate the optimal dose to be used for long-term releases in the project.