Evaluation of the Impact of the Fruit Fly ParasitoidDiachasmimorpha 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 pests 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-rearedD. longicaudataon a nontarget gall-forming tephritidEutreta xanthochaeta(Aldrich), which was introduced to Hawaii for control of the noxious weedLantana camaraL. In field cages, we presented galled lantana twigs to gravidD. longicaudatain 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 ofB. dorsalisand its food substrate,D. longicaudatahad only minimal response (visits and probes) to galled lantana patches andE. xanthochaetagalls. 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 ofB. dorsalis,and 0% parasitism in the presence ofB. dorsalis.However, 26% ofB. dorsalispresent in the cages were parasitized by releasedD. longicaudata.In the field study, about 3600 gravid femaleD. longicaudatawere released in three patches of lantana plants infested withE. xanthochaetagalls 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 155E. xanthochaetagalls successfully grew to mature (pupal) stages in parasitoid-release sites and nonrelease sites, respectively. Among those matured galls, 0.8% were parasitized byD. longicaudatain parasitoid release sites, and 0% were parasitized in nonrelease sites. In contrast, 37.5% ofB. dorsaliswere parasitized byD. longicaudatawhen 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 withD. longicaudatawill be unlikely to cause significant losses of lantana gall fly populations or negatively impact the biological control of lantana weeds.