Parasitization of melon fly (Diptera: Tephritidae) by Fopius arisanus and Psyttalia fletcheri (Hymenoptera: Braconidae) and the effect of fruit substrates on host preference by parasitoids

Fopius arisanus and Psyttalia fletcheri are egg and larval parasitoids, respectively, of tephritid fruit flies including the melon fly, Bactrocera cucurbitae. We investigated the consequences of parasitization when eggs or larvae of melon flies were exposed to F. arisanus or P. fletcheri alone, or to both in succession. In addition, we evaluated the effect of fruit substrates on host preference by gravid parasitoids. F. arisanus parasitized 45% of melon fly eggs in the cohort after a 24-h exposure period. The proportion of parasitized hosts increased 2-fold when melon fly larvae were exposed to P. fletcheri alone, or when host immatures were exposed sequentially to both parasitoids. While P. fletcheri could readily develop on melon fly, F. arisanus rarely produced progeny. Life table calculations indicated that parasitization by F. arisanus resulted in host kills of 38, 40, and 47% in egg, larval, and pupal stages of the melon fly, respectively, while parasitization by P. fletcheri resulted in larval and pupal mortalities of 24 and 79%, respectively. Sequential exposure of melon fly eggs to F. arisanus, then larvae to P. fletcheri, resulted in host kills of 52, 56, and 91% during the egg, larval and pupal stages, respectively. Parasitization by F. arisanus, P. fletcheri, or both, suppressed melon fly development by 2-, 5-, and 12-fold, respectively. Given a choice of fruit types, F. arisanus and P. fletcheri preferred melon fly in zucchini squash, Cucurbita pepo, over those in Japanese eggplant, Solanum melongena, Chinese bitter melon, Momordica charantia, Japanese cucumber, Cucumis sativus, and tomato, Lycopersicon esculentum. This study provides basic information needed for future work on single or multispecies releases of parasitoids for biological control of the melon fly.