Physiology vs. environment: what drives oviposition decisions in mango fruit flies (Bactrocera invadens and Ceratitis cosyra)?

In frugivorous insects, the physiological state of the female (e. g. age, egg load) as well as environmental parameters like fruit availability and characteristics may affect oviposition decision, host choice and the resulting clutch size. We studied host acceptance and clutch size decision as a function of fly egg load as physiological state and mango variety and ripeness stage as the environmental parameter in two major mango pests in sub-Saharan Africa, Bactrocera invadens and Ceratitis cosyra, under laboratory conditions. In addiction, egg maturation dynamics were investigated because for both species, egg production had never been explored before. Female egg load was the most important factor influencing host acceptance in both species. With respect to fruit characteristics, ripeness stage was significant for oviposition decisions only in C. cosyra. In particular, ripe and fully ripe fruits had more probability of oviposition than unripe ones. In contrast, fruit variety affected clutch size in B. invadens, with, respectively, the local variety Ngowe receiving the biggest clutches and the export Kent the smallest. Moreover, the invasive species showed a significantly higher egg production compared with the native species. Implications in terms of competitive displacement between the two species are also discussed.