Effect of γ-radiation on fertility and survival of Aedes albopictus (skuse) males in the laboratory for Sterile Insect Technique

Abstract

BACKGROUND: It is believed that Aedes albopictus, one of the dengue vectors in Sri Lanka can be controlled using Sterile Insect Technique (SIT) when integrated with other conventional control methods. The objective of this study was to determine the effective dose of gamma radiation for producing sterile males of Ae. albopictus mosquitoes. METHODS: A batch of male pupae (n=32) aged 24-48 hours in F1 was irradiated using a gamma-ray irradiator (Gamma 220, Atomic Energy of Canada Ltd., Co60) with 25 Gy in duplicates. Following the same procedure, different doses (30 Gy, 40 Gy, 50 Gy, 60 Gy and 70 Gy) were given to each pupal batch in duplicates. Then they were transferred to laboratory cages (30 cm X 30 cm X 30 cm) for emergence and supplied with 10% sucrose solution. Adult emergence rate and male longevity were recorded. Virgin females from the same cohort (F1) were introduced into each cage for mating and fed blood starting 5 days after emergence. Females were then isolated in to individual tubes and hatching rate of individual egg batches was determined after two weeks of egg maturation in hatching solution containing 0.25 g BNB, 0.05g BY in 700 ml distilled water. Spermachecae of female mosquitoes were dissected and insemination rates were calculated after egg laying. RESULTS: Male mosquito pupae in F1 showed low mortality (0-3.12%) immediately after exposing to radiation (0-48 hours). After 21 days of the irradiation, probability of survival of male mosquitoes in F1 were 0.578, 0.494, 0.453, 0.313, 0.328, 0.381 and 0.219 at 0Gy, 25 Gy, 30 Gy, 40 Gy, 50 Gy, 60 Gy and 70 Gy respectively (Kaplan Meier survival analysis). Log Rank test indicated significant differences of survival of control males with males irradiated at 40Gy, 50 Gy, 60 Gy and 70 Gy. The survival of males irradiated at 25 Gy and 30 Gy did not differ from each other and from the control. The survival of males irradiated at 40 Gy, 50 Gy, 60 Gy were not significantly different among each other. The mean hatching rate (Mean+SE) of the F2 progeny of Ae. albopictus males (F1 progeny) were 10.89+2.76%, 7.36+1.75%, 3.09+0.71%, 0.79+0.27%, 0.66+0.23% and 0% when irradiated at 25 Gy, 30 Gy, 40 Gy, 50 Gy, 60 Gy and 70 Gy respectively. The control group showed a hatching rate of 64.26 + 7.12%. It was found that insemination rate of the irradiated males among different doses and controls were above 90% in F1 based on spermatheca dissection of blood-fed females (F1). CONCLUSION: 50 Gy is recommended as the most suitable γ radiation dose to produce 99% sterility in Ae. albopictus males which has 0.328 survival probability after 21 days of irradiation. This dose can be used to produce sterile males of Ae. albopictus for population suppression.