Interspecific mating of introduced, sterile Bactrocera dorsalis with wild B-carambolae (Diptera : Tephritidae) in Suriname: a potential case for cross-species sterile insect technique

Copulation with sperm transfer was observed between the oriental fruit fly, Bactrocera dorsalis (Hendel),and the carambola fruit fly, B. carambolae (D rew & Hancock), in outdoor field cages in Suriname. Sterilized oriental fru it flies from Hawaii were shipped to Suriname for testing against wild cara mbola fruit flies to investigate whether the oriental fruit fly could be us ed in a potential sterile insect program against the carambola fruit fly. O f 217 total observed copulations on 5 test dates, 17 (7.8%) were interspeci fic, and 10 (4.6%) were of the crucial type, sterile oriental fruit fly mal e x wild carambola fruit fly female. 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 By male x orien tal fruit fly female, whereas only 4.67 min for oriental fruit fly male x c arambola fruit fly female at a 5:1 oriental fruit fly:carambola fruit fly r atio). 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 mi n for oriental fruit fly male x oriental fruit fly female and caramlola fru it fly male x carambola fruit fly female, respectively. With both sexes pre sent, oriental fruit flies began mating earlier in the evening (approximate to 2,500-lux), whereas carambola fruit flies started mating at approximate to 300 lux. With only sterile male oriental fruit flies released, the prop ortion of interspecific pairs (oriental fruit fly male x carambola fruit fl y female) rose to 1/3 of the total, at a sterile male: wild male 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 o f bisexual oriental fruit fly. Approximately 70% of carambola fruit fly fem ales that copulated with carambola fruit fly males had sperm in their sperm athecae. By comparison, 0% (0/6 flies) were mated in the case of carambola fruit fly female mated to oriental fruit fly male when both oriental fruit fly sexes were present, whereas 50% (2/4 dies) were mated when males-only o riental fruit fly were released.