Exploration for olive fruit fly parasitoids across Africa reveals regional distributions and dominance of closely associated parasitoids

Authors: Wang, Xingeng; WALTON, VAUGHN - University Of Oregon; Hoelmer, Kim; PICKETT, CHARLES - California Department Of Food And Agriculture; BLANCHET, ARNAUD - European Biological Control Laboratory (EBCL); STRASER, ROBERT - University Of California; KIRK, ALAN - European Biological Control Laboratory (EBCL); DAANE, KENT - University Of California

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2021
Publication Date: 3/17/2021
Citation: Wang, X., Walton, V.M., Hoelmer, K.A., Pickett, C.H., Blanchet, A., Straser, R.K., Kirk, A.A., Daane, K.M. 2021. Exploration for olive fruit fly parasitoids across Africa reveals regional distributions and dominance of closely associated parasitoids. Scientific Reports. 11: 6182. https://doi.org/10.1038/s41598-021-85253-y.
DOI: https://doi.org/10.1038/s41598-021-85253-y

Interpretive Summary: The olive fruit fly, native to Sub-Saharan Africa, is a key pest of cultivated olives worldwide, largely due to a lack of effective natural enemies in the invaded regions. To develop a biological control program for this pest in North America, we surveyed for effective natural enemies throughout the fly’s native range in Africa. We discovered several effective species of parasitic wasps for biological control of this pest and analyzed their seasonal and geographic abundance in relation to different climates within Africa. The regional dominance of the various parasitoid species is strongly correlated with climate. This information will help in selecting species or strains of parasitic wasps that are not only effective for the control of the fly but also capable of adapting to the climatic zones in the fly’s invaded regions.

Technical Abstract: Braconid parasitoids have been used widely in biological control of fruit-infesting tephritids worldwide. Native to Sub-Saharan Africa, the olive fruit fly, Bactrocera oleae, has long been a key invasive pest of olives in the Mediterranean basin and North America. From 2000-2011, we conducted the largest modern exploration for the fly’s co-evolved parasitoids across Sub-Saharan Africa (Kenya, Namibia, and South Africa) and some of the fly’s expanded African regions (Canary Islands, Morocco, Tunisia and Réunion Island), as well as collections outside of Africa in Pakistan, China and India. In the Sub-Saharan regions, four native braconids, Psytallia lounsburyi, P. humilis, Utetes africanus and Bracon celer were collected, primarily from wild olives. Psytallia lounsburyi, P. humilis and U. africanus were commonly sympatric, whereas B. celer was more commonly isolated. Principal Component Analysis showed that the regional dominance of these parasitoid species was related to climate niches, with P. lounsburyi the dominant species in the more mild tropical sampled areas of Kenya, P. humilis dominant in the hot semi-arid areas of Namibia and U. africanus most prevalent in the Mediterranean climates of South Africa. The native braconid Psytallia concolor was found in the Canary Islands, Moroccan and Tunisian samples, and the introduced braconid Diachasmimorpha longicaudata was collected in Réunion Island. In South Africa, seasonal monitoring of B. oleae showed a consistently low fruit infestation rate in unripe (< 5%) or ripe (< 15%) fruits. Multivariate analyses suggest that fruit maturity, seasonal climates and interspecific interactions may shape the local diversity of parasitoid complex that effectively regulates olive fruit fly populations at low levels. The results are discussed with regard to ecological adaptations of these co-evolved parasitoids to the olive fruit fly and its close relatives, and how their adaptation impact biological control of this pest in its invaded regions.