Interaction between weaver ants, mango infesting fruit flies and their exotic parasitoids

Competitive and trophic interactions can be important forces determining the structure of ecological communities. As the effects of these interactions result from the behaviour adopted by individuals, investigating individual decision making processes helps understanding the mechanisms that mediate such interactions. Such an understanding can be crucial also for applied sciences, such as the planning of biological control programs. This research investigated competitive and trophic interactions in a predator-parasitoid-pest system in sub-Saharan Africa. It involved two mango infesting fruit flies as pest, i.e., the invasive Bactrocera dorsalis, and the indigenous Ceratitis cosyra. The parasitoids were the exotic Fopius arisanus and Diachasmimorpha longicaudata, attacking eggs and larvae of the flies, respectively. Both had been released to control the fruit flies. Finally, the predator, was the African weaver ant, Oecophylla longinoda, an indigenous generalist predator in Kenya. Studies of the oviposition behaviour of the two fruit fly species revealed important differences between the fly species leading to a competitive advantage of B. dorsalis over C. cosyra. While both species increased oviposition probability with egg-load and either fruit ripeness (C. cosyra) or fruit type preference (B. dorsalis), the more fecund B. dorsalis produced larger clutch sizes. Moreover, both fly species preferred to exploit previously made oviposition punctures and thus increased their oviposition rate by saving drilling time, but while C. cosyra preferred con-specific over heterospecific punctures, B. dorsalis used punctures indiscriminately. The presence of weaver ants severely impacted oviposition behaviour in both, fruit flies and parasitoids. Direct observations revealed that encounters with ants reduced fruit fly and parasitoid foraging behaviour on mango fruits. Using weaver ants and parasitoids to control the two fruit fly species is discussed.