The braconid parasitoid Fopius arisanus (Sonan) (Hymenoptera: Braconidae) is a candidate for augmentative biological control of tephritid fruit flies. In the Puna district of Hawaii Island, F. arisanus parasitized 41–72% of oriental fruit flies, Bactrocera dorsalis (Hendel), in wild common guava, Psidium guajava L.; strawberry guava, Psidium cattleianum Sabine; and tropical almond, Terminalia catappa L. In commercial papaya, Carica papaya L., in the same region, parasitism was only 22% in tree-collected fruit and 3% in ground-collected fruit. The low level of parasitism in papaya suggests that wild parasitoids may not track the host flies well in commercial fruit and that augmentative parasitoid releases could potentially increase parasitism and thus suppress host fly populations in this habitat. The very low parasitism in ground-collected papaya suggests that F. arisanus may avoid foraging on ground fruit. Field cage experiments support this hypothesis. Numbers of females observed on tree fruit were two-fold higher than on ground fruit in small cages and 4–6-fold higher in large cages. In an experiment conducted in a papaya orchard, sentinel fruit was placed within the canopy, on the trunk, or on the ground. Parasitism was significantly higher in the canopy-placed fruit in only one of three trials. This variable response to ground fruit in the field suggests that augmentative parasitoid releases may have a significant, albeit reduced, effect on host populations under conditions of poor sanitation.
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Vol. 100 • No. 4