Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2010
Publication Date: 11/12/2010
Citation: Wang, X., Johnson, M.W., Yokoyama, V.Y., Pickett, C.H., Daane, K.M. 2010. Comparative evaluation of two olive fruit fly parasitoids under varying abiotic conditions. Biocontrol. 56:283-293. Interpretive Summary: Olive fruit fly is a key pest in olives and biological control with imported insect parasites is an environmentally friendly method to reduce infestations in California olive groves. Two small species of parasitic wasps originally found in Africa were compared for adaptation to olive fruit fly in different sized olive fruit grown in different regions of the state. One species, Psyttalia humilis, was more effective in laying eggs in olive fruit fly larvae feeding inside small olive fruit than the other species and considered a better candidate for biological control of the pest. The research helps support the olive industry in California, which is the sole producer of canned olives for the nation.
Technical Abstract: The olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae) invaded California around 1998 and has become a major olive pest. Two larval parasitoids, Psyttalia lounsburyi (Silvestri) and P. humilis (Szépligeti) (both Hymenoptera: Braconidae) were introduced from Africa into California and permitted for field release for the control of B. oleae. P. lounsburyi is more of a specialist on B. oleae while P. humilis also attacks other tephritid species. We evaluated the effectiveness of the two parasitoids (including two populations of P. humilis from Kenya and Namibia) in field cage tests in the San Joaquin Valley of California and central costal California. Twenty-six tests were conducted throughout olive growing seasons during 2006-2009 and on two distinctly different-sized cultivars. Parasitism of larval B. oleae by either parasitoid species was higher on smaller fruit cultivar ‘Manzanilla’ than on larger fruit cultivar ‘Ascolana’, and by P. humilis (both populations) was always higher than by P. lounsburyi, regardless test location and fruit size. The highest parasitism by each species was observed in climate mild seasons and high temperatures and low humidity in summer reduced the levels of parasitism by both parasitoids. The results also suggest that host specificity by P. lounsburyi does not confer a higher efficiency in this case, as fruit enlargement of domesticated olives may limit the access of the larval parasitoids to host larvae especially for the specialized P. lounsburyi than P. humilis; the latter species has relatively a longer ovipositor than the former one.