Reproductive isolation and genetic variation between two "strains" of Bracon hebetor (Hymenoptera: Braconidae)

Bracon hebetor Say(Hymenoptera: Braconidae) is known primarily as a parasitoid of pyralid moth larvae infesting stored grain. In the 1970s, a parasitoid identified as B. hebetor was released for control of Heliothis/Helicoverpa spp. (Lepidoptera: Noctuidae) on the island of Barbados. Because life-history traits of this parasitoid differed from those reported for B. hebetor from the United States, we conducted a series of laboratory experiments to determine whether this parasitoid was a population of B. hebetor that attacks noctuids in the field or a different species from B. hebetor. We confirmed that Heliothis virescens (F.) was a more suitable host for the Barbados strain than for B. hebetor: However, a stored-grain infesting pyralid, Plodia interpunctella (Hubner), was a more suitable host for the Barbados strain than was H. virescens. Reciprocal crosses between the Barbados strain and B. hebetor showed that the two populations were reproductively isolated. No mating was observed during a series of 30-min observations of reciprocal crosses, and the crosses produced only male offspring. Examination of each female's spermatheca confirmed that females were not fertilized. Sequence analysis of a 517-bp fragment of the mitochondrial 16S rRNA gene revealed that two populations of B. hebetor from our laboratory were identical but differed in sequence by 2% from the Barbados strain. Collectively, our results indicate that the Barbados strain is a distinct species from B. hebetor