REPRODUCTIVE ISOLATION AND GENETIC-VARIATION BETWEEN 2 STRAINS OF BRACON-HEBETOR (HYMENOPTERA, BRACONIDAE)

Bracon hebetor Say(Hymenoptera: Braconidae) is known primarily as a pa rasitoid of pyralid moth larvae infesting stored grain. In the 1970s, a parasitoid identified as B. hebetor was released for control of Heli othis/Helicoverpa spp. (Lepidoptera: Noctuidae) on the island of Barba dos. Because life-history traits of this parasitoid differed from thos e reported for B. hebetor from the United States, we conducted a serie s of laboratory experiments to determine whether this parasitoid was ( i) a population of B. hebetor that attacks noctuids in the held or (ii ) a different species from B. hebetor. We confirmed that Heliothis vir escens (F.) was a more suitable host for the Barbados strain than for B. hebetor. However, a stored-grain infesting pyralid, Plodia interpun ctella (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 isolate d. No mating was observed during a series of 30-min observations of re ciprocal crosses, and the crosses produced only male offspring. Examin ation of each female's spermatheca confirmed that females were not fer tilized, Sequence analysis of a 517-bp fragment of the mitochondrial 1 6S rRNA gene revealed that two populations of B. hebetor from our labo ratory were identical but differed in sequence by 2% from the Barbados strain. Collectively, our results indicate that the Barbados strain i s a distinct species from B. hebetor. (C) 1997 Academic Press.