The Effects of Age at First Mating and Release Ratios on the Mating Competitiveness of Gamma Sterilised Aedes albopictus Males under Semi Field Conditions

Abstract

Background The success of the Sterile Insect Technique for areawide vector control relies crucially on the ability of sterile males to outcompete their wild counterparts for mating with wild females. Competitiveness tests are commonly performed for assessing quality sterile males intended for field release programs, but there are few reports on the optimal age and ratio for sterile Aedes albopictus male release in a SIT program. Objective Here, a series of mating competitiveness experiments with different age (1, 3, and 5 d post-emergence) and ratios (1:1, 5:1, and 10:1) of sterile to wild males were carried out in a walk-in field cage under semi-field conditions to examine variations in the mating competitiveness of irradiated adult Ae. albopictus males. Methods Pupae from laboratory-reared Ae. albopictus were irradiated at 35 Gy and introduced in field cages at different ages post emergence and at different ratios with a cohort of wild males and females. The mating competitiveness of sterile versus fertile males, and sterility induction into wild females measured through the egg hatch were observed. Results The age of sterile males Ae. albopictus significantly affected their competitiveness when confronted with wild males of the same age. Competitiveness of sterile males was significantly lower after emergence (1-day old) than when they were older (3-5 days old). Presumably, 3-days old sterile males may be considered as the optimal age for sterile male releases. At this optimal age, induced sterility rates increased as the proportion of irradiated males relative to the wild male increased. Conclusion Our study points to the fact that sugar feeding prior to field release, could be administered for 3 days post-emergence in order to enhance the performance of sterile males. Consistent with early investigations under competitive situations differing in sterile male-to-wild male ratio, the level of induced sterility in the wild females increased as the proportion of irradiated males relative to the wild male increased.