Mechanisms contributing to the competitive success of the invasive fruit fly Bactrocera invadens over the indigenous mango fruit fly, Ceratitis cosyra: the role of temperature and resource pre-emption
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We investigated the influence of temperature and infestation sequence on interspecific competition between two fruit flies: an invasive (Bactrocera invadens Drew, Tsuruta & White, (B) and a native (Ceratitis cosyra Walker, C) (both Diptera: Tephritidae) species. Mango fruits [Mangifera indica L. (Anacardiaceae)] were co-infested with larvae at different constant temperatures (15, 20, 25, and 30 °C) and relative humidity of 50 ± 8%, using different infestation sequences at each temperature (BC together; BC/CB 1, 2, and 3 days apart). There were significant effects of competition in most experimental treatments, resulting in reduced larval survival, pupal mass, and adult emergence for both species. At most of the infestation/temperature combinations, C. cosyra was clearly the inferior competitor. The only exception was at 20 °C when the outcome depended on the sequence of infestation: no C. cosyra survived when the sequence was BC, but more C. cosyra than B. invadens survived when it was CB. At 15 °C, all C. cosyra larvae died, while the development of B. invadens was prolonged and adult emergence reduced. We conclude that resource pre-emption and fluctuations in temperature in mango agroecosystems help to explain observed shifts in dominance between B. invadens and C. cosyra on mango in many parts of Africa. The small window of competitive superiority for C. cosyra at 20 °C and CB infestation sequence, together with other factors such as fecundity and alternative hosts, may allow for co-existence in some environments.