Mating Competitiveness of Bactrocera dorsalis (Diptera: Tephritidae) Males From a Genetic Sexing Strain: Effects of Overflooding Ratio and Released Females

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a global pest that infests a range of fruit and vegetables. Males are attracted to methyl eugenol, and control is often achieved by the Male Annihilation Technique, where methyl eugenol + insecticide dispensers are deployed to eliminate males, preclude matings, and reduce population growth. The Sterile Insect Technique (SIT) has also been used to control B. dorsalis. The SIT involves the release of mass-reared, sterilized males to achieve matings with wild females, who then produce inviable eggs. Two key elements of SIT include the overflooding ratio achieved (sterile: wild males) and the strain type utilized, namely bisexual or genetically sexed (allowing male-only releases). Here, we describe the effects of these two factors on the mating competitiveness of a males from a genetic sexing strain of B. dorsalis, termed DTWP. Mating success was scored for DTWP versus wild males in field cages at ratios of 1:2, 1:1, 2:1, and 10:1 both when DTWP females were or were not concurrently released with DTWP males. Close correspondence was found between observed numbers of matings of particular male-female combinations and expected numbers based on the numbers of flies released of each sex and each strain. As a result, the proportion of total matings achieved by the DTWP across the eight treatments showed a corresponding increase with overflooding ratio. At a given ratio, DTWP males had a higher relative mating success when DTWP females were absent rather than present, although the reason for this was unclear.