Biological control of olive fruit fly in California

Authors: Wang, Xingeng; DAANE, KENT - California Department Of Food And Agriculture; PICKETT, CHARLES - University Of California; Hoelmer, Kim

Submitted to: Contributions of Classical Biocontrol to the U.S. Food Security, Forestry, and Biodiversity, 1985-2022
Publication Type: Book / Chapter
Publication Acceptance Date: 4/21/2022
Publication Date: 6/21/2022
Citation: Wang, X., Daane, K.M., Pickett, C.H., Hoelmer, K.A. 2022. Biological control of olive fruit fly in California. Contributions of Classical Biocontrol to the U.S. Food Security, Forestry, and Biodiversity, 1985-2022. 115-126.

Interpretive Summary: The olive fruit fly is native to Sub-Saharan Africa. It was first detected in 1998 in California and since then has become a key olive pest. To develop a biological control program for this pest, researchers conducted extensive surveys for effective natural enemies across the fly’s native range and systematically evaluated candidate natural enemies. Two parasitic wasp species were selected, mass-reared and widely released in California in recent years. One of these natural enemies has become established along the California coastal olive growing regions and may provide substantial control of the fly in the future.

Technical Abstract: The olive fruit fly, Bactrocera oleae (Diptera: Tephritidae), was first detected in 1998 in southern California. It was soon found in all olive-growing regions in California, becoming the most destructive olive pest in this region. Control relies on frequent insecticide applications, most commonly bait formulations that target adult flies. Pest control is hampered by the large number of unmanaged olive trees that can act as sources of flies moving into treated commercial orchards. To develop better sustainable olive fruit fly management, researchers in California conducted the largest modern exploration for natural enemies across the fly’s native range, imported to quarantine laboratories, evaluated potentially suitable parasitoids, and developed information needed for USDA-APHIS permits for release of selected species. Two wasp species (Psyttalia humilis and Psyttalia lounsburyi, both Hymenoptera: Braconidae) were approved for field release. For P. humilis, 360,240 (Kenyan strain) and 42,591 (Namibian strain) were released in seven coastal and eight interior valley counties from 2006 to 2013. Although P. humilis showed initial promise in quarantine studies, permanent field establishment was not detected. For P. lounsburyi, 22,391 (South African strain) and 64,026 (Kenyan strain) were released in 12 coastal and four interior valley counties from 2006 to 2017. Psyttalia lounsburyi has permanently established and expanded its range along the coast, with the highest levels of fly larval parasitism reaching 39.9–73.5% within a few years of the initial release. However, P. lounsburyi has not yet been recovered in interior valley counties, and its densities in coastal areas appear to be falling. At present, it does not appear that P. lounsburyi will significantly suppress olive fruit fly populations, especially in the important agricultural regions in the interior valleys. Continued biological control efforts for olive fruit fly may seek parasitic wasp species or strains that have biological traits better suited to California’s interior valley.