Effect of olive fruit size on the parasitism rates of Bactrocera oleae (Diptera: Tephritidae) by the figitid wasp Aganaspis daci (Hymenoptera: Figitidae), and first pilot field releases of adult parasitoids in an organic olive grove

Abstract: The olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is the most serious pest of the olive production worldwide. Aganaspis daci (Hymenoptera: Figitidae) is a larval- prepupal endoparasitoid that successfully attacks several fruit fly (Tephritidae) species. To assess the potential of A. daci as a biological control agent against B. oleae, we studied, under laboratory conditions, the effect of olive fruit size on parasitism rates of A. daci on 2nd and 3rd instar larvae of B. oleae. In addition, we conducted pilot scale releases of A. daci females in a 0.5 ha organic olive grove. We released 1000 A. daci females/week from July to October. Extensive olive fruit sampling was performed to to estimate olive fruit infestation levels and the parasitism rates of A. daci. Laboratory trials revealed that both the size of the fruit and the larvae instar were significant predictors of parasitism success of A. daci when the cultivar Chalkidikis was considered. Parasitism rates were higher in small-size fruit compared to bigger and medium ones. The 3rd instar larvae of B. oleae were parasitized in higher levels compared to younger instars. Interestingly, no successful parasitism was observed in the wild olives irrespective of the developing larvae instar (2nd or 3rd). The pilot field trials revealed no recovery of A. daci adults from the sampled olive fruits that were infested by the olive fly. Apparently, higher number of parasitoids should be considered in future trials aiming to successful control of B. oleae in the wild. We discuss the importance of biological control for the management of the olive fruit fly.