An undescribed wasp, Pteromalus nr. myopitae (Hymenoptera: Pteromalidae) opportunistically parasitizes the olive fruit fly Bactrocera oleae (Rossi) (Diptera: Tephritidae), an introduced pest of olives in California. The native or typical host of P. nr. myopitae is unknown. We demonstrate that P. nr. myopitae is a solitary, ectoparasitic, idiobiont parasitoid of the third instar host inside fruit, and pupation occurs in the host tunnel. Reproduction of P. nr. myopitae on B. oleae in olives in the laboratory and in field cages generally failed. Host-feeding was not observed, and adults fed honey and water lived longer than those provided with water alone. Parasitism in non-commercial olives in the moderate coastal climate of San Luis Obispo occurred primarily from August to October, and was absent from a nearby location with more extreme climate and a low population of B. oleae. Greater parasitoid numbers were associated with greater host densities, and proportion of hosts parasitized was generally higher at lower host densities during 2 years of the study. The geographic range of the parasitoid extends along the coast from San Francisco Bay to Ensenada, Baja California, Mexico, and also inland in the Sacramento Valley, with one record in the San Joaquin Valley. The potential of the parasitoid as a biological control agent of B. oleae is probably low, however, the extent of its interference with other parasitoids being considered for release in California is unknown and warrants further study.


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