Queensland fruit fly, Bactrocera tryoni, is one of Australia’s most damaging fruit fly pests. Male Annihilation Technique (MAT) is a method used to manage fruit fly populations by luring and killing male flies, which limits population growth by preventing female flies from mating. MAT devices consist of an attractant and a toxicant, such as maldison or fipronil. Fipronil has a slow knockdown effect, which has been exploited to induce indirect toxicity of a number of insect pests, including cockroaches and termites. This indirect effect, called horizontal transfer, is facilitated through the sharing of food or contact with exposed individuals. Horizontal transfer has been reported in Queensland fruit fly, where exposed males have transferred lethal doses of fipronil to virgin females during courtship and mating. In the present study, we explored three possible modes of horizontal transfer of fipronil against Queensland fruit fly under laboratory conditions. These included: (1) direct contact of females with exposed males (2) contact of males to the regurgitant of exposed males and (3) contact of males with dead exposed males. Our results demonstrated that lethal doses of fipronil were not transferred from males to females during courtship and mating. Male flies that were exposed to fipronil one and six hours prior to dusk were all knocked down, moribund or dead at dusk and therefore did not participate in courtship displays or mating. However, we found that horizontal transfer and subsequent death occurred in males that fed on the regurgitant of exposed males, and in males that were in contact with dead exposed males. Therefore, MAT devices that contain fipronil should not be used as a standalone treatment but rather be used in combination with other control methods, such as protein bait sprays to ensure the control of female flies
