Submitted to: Journal of Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/7/2009
Publication Date: 1/20/2009
Citation: Wang, X., Johnson, M.W., Daane, K.M., Yokoyama, V.Y., Pickett, C.H. 2009. Enlargement of cultivated olive fruit reduces the efficiency of the larval olive fruit fly parasitoid Psyttalia concolor. Journal of Biological Control. 49: 45-51. Interpretive Summary: A parasitoid wasp imported by the USDA-ARS in Parlier, CA from the USDA-APHIS-PPQ lab in Guatemala was found to control the larval stage of olive fruit fly, a pest in California olives, by stinging the larvae in infested fruit. Adult parasitoids reared from Mediterranean fruit fly in Guatemala are larger than those reared on olive fruit fly in California. If the parasitoid was imported, released, and developed in olive fruit fly, the next generation may become smaller in size than the imported parents. A loss in parasitoid size may cause a reduction in parasitization efficiency because the stinger or ovipositor would be shorter, and the parasitoids would not be able to reach the larval stage of the pest in large fruit. Laboratory and field cages studies were conducted by the University of California in Parlier to investigate the effect of olive fruit size and parasitism of olive fruit fly larvae in relation to parasitoid ovipositor length. Parasitism was shown to be higher in small than large fruit, and large parasitoids were more efficient than small parasitoids. The parasitoid has shown a high level of olive fruit fly control when adults are released in the coastal areas of California where olive fruit fly is abundant. These regions consist primarily of small Mission type olives used to produce oil. The findings support the continued use of imported parasitoids for biological control of olive fruit fly in the coastal regions of California which are reservoirs of the pest.
Technical Abstract: Cultivated olive fruit are greatly enlarged as a result of domestication. In this study, we examined the effects of fruit size within a cultivar (Sevillano) and across four different-sized cultivars (in order of decreasing size: Sevillano, Ascolano, Manzanillo, and Mission) grown in California on the parasitization efficiency of a larval parasitoid, Psyttalia concolor (Wharton) on the olive fruit fly, Bactrocera oleae (Rossi). The effect of fruit size on the parasitism was examined under two different host distributions: a variable host distribution (determined by flies) where host density increased with fruit size, and a uniform host distribution (manipulated) where host density was similar across fruit. Regardless of host distribution and cultivar, parasitism by P. concolor was consistently higher on small than large fruit. Field-cage release tests also showed that the parasitism of larval B. oleae by P. concolor was higher on the largest cultivar (Sevillano) than on the smallest cultivar (Mission). Large fruit seemed to create a structural refuge for larval B. oleae due to the relatively short-ovipositor of P. concolor. However, body size as well as the ovipositor length of P. concolor was enlarged when female wasps developed from the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), compared with those reared from B. oleae. Consequently, female wasps reared from C. capitata were more efficient than those developed from B. oleae. We discuss the potential implications of these findings for biological control of B. oleae.