The semiochemistry of fruits as seen through the lens of Tephritid fruit flies and their parasitoids

Abstract

The tephritid fruit fly is a term well-known in fruit and vegetable production. Several techniques including the use of parasitoids have been deployed for fruit fly control. In Sub-Saharan Africa, Fopius arisanus (Sonan) and Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) have been introduced to supplement the existing native parasitoids. Although the effectiveness of parasitoids is known, there is a knowledge gap in the semiochemical-mediated interactions among tree-attached fruits, fruit flies, and parasitoids. Here, I aimed to compare the attraction of fruit flies and parasitoids to different fruits, evaluate fruit fly performances, in terms of recovered puparia, in these fruits and elucidate the fruits’ headspace volatile compounds. First, the attraction of Bactrocera dorsalis (Hendel), F. arisanus and D. longicaudata to the headspace volatiles of different treatments of three varieties of mangoes were compared. B. dorsalis and the two parasitoids were differentially attracted to the mango headspace volatiles compared to the control, clean air. A higher number of B. dorsalis puparia was recovered in the Apple mango variety (81.7%) but none from the Kent variety. Gas chromatography- mass spectrometry revealed several organic compounds with qualitative and quantitative differences. The majority of tentatively identified compounds were esters (33.8%). Most compounds were produced at higher concentrations by fruit fly-infested mangoes than non-infested ones. A similar approach to B. dorsalis' was followed on Ceratitis cosyra, the two parasitoids and its native Psyttalia cosyrae (Wilkinson). C. cosyra and the parasitoids differentially responded to the treatments of the three mango varieties. Ceratitis cosyra performed better in Kent mango (72.1% of the 287 puparia recovered) compared to Apple and Haden varieties. Esters were the main components of the non-infested ripe and the late post-oviposition larval stages of the three mango varieties. At the same time, monoterpenes and sesquiterpenes were dominant in the other mango treatments. The performances of B. dorsalis, C. cosyra, Zeugodacus cucurbitae and B. latifrons on different species of fruits (mango cv. Haden, banana cv. Fhia-17, and tomato cv. Improved Nouvelle F1) were investigated and the headspace volatiles of different treatments of the three mango varieties, ripe bananas and tomatoes analyzed using GC-MS and GC-electroantennographic detection (EAD). The fruit fly species performed differentially in the different fruits. There were overlapping detections of most EAD-active compounds across the four fruit fly species and parasitoids with esters being the most prevalent class of compounds. This study represents the first report of the interactions of different fruit fly species and their parasitoids to in situ headspace volatiles of different treatments of mangoes and the subsequent changes in the headspace components of these mango treatments. Results obtained not only provide a better understanding and add new knowledge to science on the dynamic interactions of the selected tephritid fruit fly species and their parasitoids to a variety of hosts with different physiological states but also show a convergence of fruit fly and parasitoid antennal-active compounds hence presenting an informed foundation for future reference in developing sound Integrated Pest Management (IPM) strategies for managing fruit flies without harming parasitoids.