Biological control of prickly acacia (Vachellia nilotica subsp. indica): New gall-inducing agents from Africa

Biological control is the most economically viable management option for prickly acacia (Vachellia nilotica subsp. indica), a serious weed of grazing areas in western Queensland, Australia. Biological control efforts so far have focused on agents from Pakistan, Kenya, South Africa and India, with limited success to date. Hence, the search for new agents, focusing on gall-inducers, was redirected to Ethiopia and Senegal, based on plant genotype and climate matching. Surveys were conducted on V. nilotica subspecies with moniliform fruits including the invasive subspecies indica. Prospective biological control agents have been identified based on damage potential, field host range and climate match. A gall thrips (Acaciothrips ebneri [Karny]) inducing shoot-tip rosette galls, a gall mite (Aceria sp. 3) deforming leaflets, rachides and shoot-tips in Ethiopia and Senegal and a tephritid fly (Notomma mutilum [Bezzi]) inducing stem-galls in Senegal have been prioritized for further studies. The gall thrips from Ethiopia has been imported into quarantine in Brisbane, Australia and host specificity tests are in progress. The eriophyid gall mite from Ethiopia has been imported into quarantine in Pretoria, South Africa and host specificity tests are also in progress there. Results to date suggest that both agents are highly host specific at the subspecies level of the target weed. Future research will focus on the host specificity testing of the tephritid gall fly from Senegal which has been imported in quarantine in Brisbane, Australia.