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Olive fruit fly (Diptera: Tephritidae)

Project Leaders: Marie Claude BON and Gaylord DESURMONT

 

Background

The olive fruit fly, Bactrocera oleae Rossi(Diptera: Tephritidae),is a widespread pest that feeds exclusively on wild and cultivated olives (Daane and Johnson 2010). The olive fruit fly is found almost anywhere cultivated olives are grown or wild olives naturally occur. The olive fruit flywas recently found in Southwestern China far to the east of all previously known records (Bon et al., 2015). The fruit fly likely originated in sub-Saharan Africa, where the wild olive Olea europaea cuspidata is found and from which the domesticated olive O.europaea europaea was derived (Nardi et al, 2005; 2010). In California, the olive fruit fly has spread to all commercial olive growing regions since first being detected in 1998. Due to the extensive occurrence of non-commercial olive trees throughout California, and low profit margin for both oil and table production olives, research into classical biological control has been a major focal point for controlling this fly (Johnson et al., 2006; Daane et al., 2011; Hoelmer et al., 2011).

Project

As part of a collaborative program initiated in 2002 with the Californian Department of Food and Agriculture (CDFA) and the University of Berkeley (CA), EBCL has carried out extensive foreign exploration in the Mediterranean region, Africa, and Asia for natural enemies which resulted in the discovery of at least five parasitoid species as potential biological control agents for the olive fruit fly in California (Daane et al., 2008; Hoelmer et al., 2011; Yokoyama et al., 2011).  Two populations (South Africa and Kenya) of one of these agents, the larval parasitoid Psytallia lounsburyi (Braconidae) which has been mainly mass-reared at EBCL (Chardonnet et al., 2019) have been successfully released and established in California (Wang et al., 2013; Daane et al., 2015).  Unexpectedly, genetic studies showed that the P. lounsburyi of South African origin predominantly established in California over the Kenyan origin, although it was less released, suggesting that it might be better adapted than the Kenyan origin to the ecological conditions found in Central and Northern California (Bon et al., 2017). The genetic features and the microbiomes of these populations might be important factors triggering the success (or the relative success) of their adaptation in California. The two populations were shown to be genetically distant and differently infected by the bacterial endosymbiont, Wolbachia sp. (Cheyppe et al., 2011). Importantly, we do not know what are the key genes or the key endosymbiotic microorganisms underlying such differences in their adaptation. Therefore, a comprehensive evaluation of these key genes and their microbiomes will help to underpin the understanding of the efficacy of this wasp as a classical biological control agent. 
Another parasitoid, P. ponerophaga, was collected by CABI Pakistan for EBCL and is currently reared at EBCL. Compared to P. lounsburyi, it presents different ecological and behavioral characteristics: P. lounsburyi does not need the presence of olives initiate the oviposition process but is highly host-specific; on the other hand, P. ponerophaga is highly stimulated by the presence of olives to start the oviposition process but its level of host-specificity remains to be determined. Identifying the key cues (visual and chemical) that initiate and condition the foraging and oviposition behavior of these parasitoids, as well as estimating the likelihood of these parasitoids to attack non-host species in presence and absence of these cues, would have immense value to evaluate and compare P. lounsburyi and P. ponerophaga as biolocial control agents and possibly improve their use in the field. The experimental frame of such study could be applied to other braconid species, as braconids of fruit flies in general have been of high interest for biological control practitioners worldwide. The work on P. ponerophaga host range is critical component for the olive fruit fly project and will necessitate field collections in Pakistan, the only location where P. ponerophaga is known to occur.

1
Illustration of the rearing method of P. ponerophaga used at EBCL. The central ball contains C. capitata larvae covered by a parafilm layer. Olives are used to stimulate the parasitoids to land and eventually inspect the ball.