Natural biocontrol of fruit flies in indigenous hosts: A perspective for population control in the agroecosystem

Fruit flies (Diptera Tephritidae) are a major pest to fruit production in Africa. Most efforts to control these pests are focused directly on the orchards where fruit damage has been recorded. However, fruit flies are generally able to develop on alternative indigenous fruits from which they continuously recolonize the orchards, challenging the ability to efficiently control these pests. In the natural and semi-natural environments, parasitic Hymenoptera remain the primary means of keeping populations of fruit flies at a reasonable level, but little is known about the diversity, the distribution and the ability of these parasitoids to effectively control populations. In this study, we explored the diversity and abundance of parasitoids of fruit fly pests in indigenous and exotic cultivated fruits of two separate regions of South Africa: North-East (Limpopo and Mpumalanga provinces) and South-West (Western Cape Province). A total of 16 fruit species were collected and incubated to obtain emergence of fruit flies and their associated parasitoids. Ceratitis capitata (Wiedemann), Ceratitis rosa sensu lato Karsch, Ceratitis cosyra (Walker) and Bactrocera dorsalis (Hendel) were reared from the incubated fruit. In the Western Cape Province, only C. capitata and C. rosa sensu lato were recorded. Our results show an important contrast in the distribution of fruit fly parasitoid species between regions and between indigenous fruit types. Fopius ceratitivorus Wharton and Psyttalia humilis (Silvestri) (Hymenoptera: Braconidae) dominated parasitism in the north-eastern part of the country, while fruit fly parasitoids were almost absent on fruit flies in the Western Cape Province. Parasitism rate of fruit flies ranged from 0 to ca 50% depending on fruit species and locality within a region. The exact drivers of this variation in parasitism rate remain unclear, but smaller fruits generally seem to allow better control of infesting fruit flies by parasitoids than larger ones. The fruits of some indigenous trees (Berchemia discolor (Klotzsch) Hemsl.; Syzygium cordatum Hochst. ex Krauss and Garcinia livingstonei T. Anderson) are hosts of high densities of both fruit flies and their parasitoids. These species are good candidates for the application of augmentoria for the mass production and release of biological control agents.