Due to the relatively recent invasion of exotic Tephritidae pest species the interests in Tephritidae fruit fly management increased and so also the number of studies on both the exotic and the native fruit flies and their parasitoids. The exotic Bactrocera dorsalis (Diptera: Tephritidae) causes serious damage to fruit trees thereby threatening the horticulture industry. Until now, native parasitoids of B. dorsalis have never been reared most likely owing to encapsulation of their eggs inside the host and as a result for B. dorsalis to become a sink for native parasitoids. Because of the above and the fact that Fopius arisanus (Hymenoptera: Braconidae) was at the time the most successful natural enemy in classical biological control programs of fruit flies in other parts of the world, it was shipped from a laboratory colony at icipe, Nairobi, Kenya in 2008 to IITA-Benin where it was mass-reared in an insectary for experimental releases. Studies on interspecific competition between the exotic fruit fly parasitoid, F. arisanus and native parasitoids, from the Braconidae family show that the exotic species has a competitive advantage over the native closely related F. caudatus in some fruits, although environmental requirements might affect this superiority. After several field releases, F. arisanus has been recovered in the southern part of Benin and in Cameroon. In Benin, parasitism rates ranging from 0.3 to 2.3% on Mangifera indica and from 11.6 to 46.5% on Irvingia gabonensis have been recorded in release fields. In Cameroon, the parasitism rates ranged from 0 to 2.9% on M. indica and from 0.02 to 30.8% on I. gabonensis. In Benin, B. dorsalis populations were reduced by 33-65% over the study period. Unlike in Benin, no significant reduction has yet been noted for now in Cameroon probably because F. arisanus has been only recently established. Two years after the last release, the wasp had dispersed 8 km from the release site in Benin and 2 km in Cameroon, Meanwhile IITA continues to evaluate the establishment, spread, and effect of F. arisanus as a biological control agent.
The Tephritidae guilds in West Africa have been investigated for mango, Citrus spp. and some Cucurbitaceae spp., including watermelon. Although inventories of native fruit fly parasitoids in West Africa have been made and some species still need to be identified accurately, more investigations are required to understand the Tephritidae guild phenomena. Through the years, we have observed that parasitism of Tephritidae spp. varies depending on the fruit fly species, fruit, variety, pesticide use, herb coverage, level of wilderness, and cropping system in the area. All this constitutes base knowledge for the conservation of biological control agents. In certain cases, a 30% parasitism due to native Braconidae species was reported in native Ceratitis spp.
Desire Gnanvossou: Entomologist, D.Gnanvossou@cgiar.org
Miriam Karlsson: Entomologist (SLU), M.Karlsson@cgiar.org