Abstract:
Fruit flies (Diptera: Tephritidae) are notorious pests of horticultural crops, causing significant economic losses especially in the tropics. The conventional approaches utilized in controlling these pests including biological and chemical methods are relatively inefficient and targets mostly males, making it imperative to identify new Integrated Pest Management (IPM) tools that are effective and economically sustainable. To boost current efforts in fruit fly control, females should also be controlled, for example through exploitation of their host marking behavior. Ovipositing females of certain fruit fly species have been established to mark their oviposition sites with a host marking pheromone (HMP), to deter other females from overexploiting the same fruit for egg laying. Previous work has identified HMPs for ovipositing females of the cherry fruit fly and the Mexican fruit fly. However, few are known for African indigenous fruit flies. In this study, the HMP of the African indigenous mango fruit fly Ceratitis cosyra,was identified as glutathione (GSH): - a ubiquitous animal and plant antioxidant tripeptide, while that of C. rosa and C. fasciventris is glutamic acid (GA). GSH was identified using bioassay-guided fractionation where aqueous extract of the fecal matter of adult females was analyzed by liquid chromatography coupled to quadrupole time of flight mass spectrometry (LC-QTOF-MS). A similar protocol was used to resolve the HMP of the two fruit fly species C. rosa and C. fasciventris. Dual choice oviposition assays showed that both the fecal matter extract and the isolated female specific compound significantly reduced oviposition responses in conspecific and heterospecific females of C. cosyra, C. rosa and C. fasciventris. GSH and GA levels in the respective female fecal matter extract increased with increasing age of the fruit fly, with optimal amounts detected in the fecal matter of approximately 2-week-old before slightly dropping. Additionally, GSH and GA levels were 5-10 and 10-20 times higher in female fecal matter than in the ovipositor or hemolymph extracts of the respective females fruit flies. Further analysis using synthetic GSH showed the molecule to reduce oviposition in conspecifics and the heterospecifics species (C. rosa, C. fasciventris, C. capitata, Zeugodacus cucurbitae) and to arrest the egg parasitoid Fopius arisanus. In contrast, GSH had no effect on oviposition responses of the invasive oriental fruit fly species Bactrocera dorsalis and C. anonae. Also, it did not alter the volatile profile of ripe mango fruit when topically applied. GA on the other hand, reduced oviposition in C. rosa and C. fasciventris but not in C. cosyra. Identification of GSH and GA as a host marking pheromone in females of C. cosyra and C. rosa and C. fasciventris improves our understanding of fruit fly chemical ecology, and that they could be used as a potential component in the IPM of these fruit fly species