Forced-contact mating: A technique for crossing experiments with the fruit fly parasitoid, Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae)

In this paper, a new technique is described for successfully manipulating the mating of a braconid parasitoid (Hymenoptera: Braconidae) of tephritid fruit flies. This forced-contact-mating technique was first developed for cross-mating experiments to determine the inheritance of winglessness in Diachasmimorpha longicaudata (Ashmead). Since female D. longicaudata only result from fertilized eggs (unfertilized eggs become males), this mating technique has advantages in the mass production of females for biocontrol releases as well as in investigations on the inheritance of the wingless trait and studies of reproductive isolation among different populations of these parasitoids. Free-mated colonies were generally all winged and predominantly male. Wingless males occurred occasionally but wingless females were rare. Virgin, winged females were immobilized by chilling and placed in close contact with wingless males. Active wingless males readily mounted and mated with immobilized female. Progeny of these mated females were all winged (not, vert, similar83% ♂ and 17% ♀). When F1 females remained unmated they produced both winged and wingless males (not, vert, similar1:1 ratio) but when immobilized F1 females were back-crossed with wingless males, both winged and wingless females (not, vert, similar5:1 ratio) were produced in addition to winged and wingless males. The wingless character was thus determined to be controlled by a recessive gene. Crossing experiments between two different Thai populations of D. longicaudata provided evidence that these populations were reproductively isolated. Among free-mated pairs, some sperm transfer occurred but almost no female progeny were produced. Similarly, among forced-mated pairs, more than double the numbers of females had sperm transferred to their spermatheca, but few female progeny were still produced. This suggests that these two populations are reproductively isolated and are part of a closely related species complex.