Evaluation of the impact of the fruit fly parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) on a nontarget tephritid, Eutreta xanthochaeta (Diptera: Tephritidae)

Diachasmimorpha longicaudata (Ashmead) is an important parasitoid introduced to Hawaii for the control of fruit fly peats and recently has been mass-reared in insectaries for use in augmentative biocontrol programs. Under field-cage and field conditions, we evaluated the potential negative impact of mass-reared D. longicaudata on a nontarget gall-forming tephritid Eutreta xanthochaeta (Aldrich), which was introduced to Hawaii for control of the noxious weed Lantana camara L. In field cages, we presented galled lantana twigs to gravid D. longicaudata in the presence or absence of its normal rearing host, Bactrocera dorsalis (Hendel), and its food substrate (infested guava fruit) in a potted guava tree. Regardless of the presence or absence of B. dorsalis and its food substrate, D. longicaudata had only minimal response (visits and probes) to galled lantana patches and E. xanthochaeta galls. As a result, 24-h exposure to the parasitoids (at a 5:1 ratio of parasitoids to available hosts) resulted in only 1% parasitism in the absence of B. dorsalis, and 0% parasitism in the presence of B. dorsalis. However, 26% of B. dorsalis present of B. dorsalis. However, 26% of B. dorsalis present in the cages were parasitized by released D. longicaudata. In the field study, about 3600 gravid female D. longicaudata were released in three patches of lantana plants infested with E. xanthochaeta galls in each of two treatment sites during a 1-month period. Over a 2-month period of sampling after the first parasitoid release, 139 and 155 E. xanthochaeta galls successfully grew to mature (pupal) stages in parasitoid-release sites and nonrelease sited, respectively. Among those matured galls, 0.8% were parasitized by D. longicaudata in parasitoid release sites, and 0% were parasitized in nonrelease sites. In contrast, 37.5% of B. dorsalis were parasitized by D. longicaudata when placed in nearby lantana patches in the parasitoid release sites, and 0% were parasitized in nonrelease sites. Together, field and field-cage results indicate that augmentation with D. longicaudata will be unlikely to cause significant losses of lantana gall fly populations or negatively impact the biological control of lantana weeds. (C) 1997 Academic Press