Mating competitiveness of Bactrocera dorsalis (Diptera: Tephritidae) males from a genetic sexing strain: Effects of overflooding ratio and released females

Authors: SHELLY, TODD - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center; Manoukis, Nicholas

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2022
Publication Date: 4/26/2022
Citation: Shelly, T.E., Manoukis, N. 2022. Mating competitiveness of Bactrocera dorsalis (Diptera: Tephritidae) males from a genetic sexing strain: Effects of overflooding ratio and released females. Journal of Economic Entomology. 115(3):799-807. https://doi.org/10.1093/jee/toac027.
DOI: https://doi.org/10.1093/jee/toac027

Interpretive Summary: This paper describes the results of mating competitiveness assays designed to test if mass reared male oriental fruit fly with a special trait for distinguishing the sexes (pupal color difference between males and females) are competitive with wild-type males. This question is important for "Sterile Insect Technique" (SIT) whereby sterile males are released to crash a population of pest insects; if the mass reared males are more competitive, the technique is more successful. We found that overall this particular strain of mass-reared males was very competitive with the wild males- performed similarly. This was true whether or not sterile females were present- though for direct comparisons the presence of DTWP females seemed to increase the mating success of DTWP males with wild females.

Technical Abstract: The oriental fruit fly, Bactrocera dorsalis (Hendel), is a major global pest that infests a broad range of fruit and vegetables. Males are attracted to the chemical methyl eugenol, and control is often achieved by the Male Annihilation Technique where a high density of methyl eugenol + insecticide dispensers are deployed to eliminate males, preclude matings, and thus reduce population growth. The Sterile Insect Technique (SIT) has also been used to control B. dorsalis outbreaks. The SIT involves the release of mass-reared, sterilized males of the pest species 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 vs. 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. Goodness-of-fit tests showed close correspondence between observed numbers of matings of particular male-female combinations (with respect to strain) and expected numbers based on the numbers of flies released of each sex and each strain. In short, the mating frequencies of DTWP and wild males across all 8 treatments indicated that females mated randomly with respect to male strain. As a result, the proportion of total matings achieved by the DTWP across the 8 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. Implications of these results for SIT against B. dorsalis are discussed.