Interspecific Mating of Introduced, Sterile Bactrocera dorsalis with Wild B. carambolae (Diptera: Tephritidae) in Suriname: a Potential Case for Cross-Species Sterile Insect Technique

Abstract

Copulation with sperm transfer was observed between the oriental fruit fly, Bactrocera dorsalis (Hendel), and the carambola fruit fly, B. carambolae (Drew & Hancock), in outdoor field cages in Suriname. Sterilized oriental fruit flies from Hawaii were shipped to Suriname for testing against wild carambola fruit flies to investigate whether the oriental fruit fly could be used in a potential sterile insect program against the carambola fruit fly. Of 217 total observed copulations on 5 test dates, 17 (7.8%) were interspecific, and 10 (4.6%) were of the crucial type, sterile oriental fruit fly ♂ × wild carambola fruit fly ♀. Interspecific copulations tended to be of short duration, especially when the male was an oriental fruit fly (i.e., average time in copula was 148.0 min for carambola fruit fly ♂ × oriental fruit fly ♀, whereas only 4.67 min for oriental fruit fly ♂ × carambola fruit fly ♀ at a 5:1 oriental fruit fly:carambola fruit fly ratio). Homogamic (like with like) pairings tended to be longer, especially for carambola fruit fly, with average times in copula of 115.7 and 481.4 min for oriental fruit fly ♂ × oriental fruit fly ♀ and carambola fruit fly ♂ × carambola fruit fly ♀, respectively. With both sexes present, oriental fruit flies began mating earlier in the evening (≈2,500-lux), whereas carambola fruit flies started mating at ≈300 lux. With only sterile male oriental fruit flies released, the proportion of interspecific pairs (oriental fruit fly ♂ × carambola fruit fly ♀) rose to return ⅓ of the total, at a sterile ♂: wild ♂ ratio of 5:1. This was 3-fold higher than for the release of bisexual oriental fruit fly. An index of mating isolation, relative isolation index, was high (>100, where random mating = 1) because of high assortative mating in the case of bisexual oriental fruit fly. Approximately 70% of carambola fruit fly females that copulated with carambola fruit fly males had sperm in their spermathecae. By comparison, 0% (0/6 flies) were mated in the case of carambola fruit fly ♀ mated to oriental fruit fly ♂ when both oriental fruit fly sexes were present, whereas 50% (2/4 flies) were mated when males-only oriental fruit fly were released.