Biological control of prickly acacia: field release and monitoring of gall thrips in Australia

Abstract

Prickly acacia (Vachellia nilotica subsp. indica) is a serious invasive weed in grazing lands of western Queensland, Australia. Among the available management strategies, biological control is the most cost-effective option. Over the past 40 years, biological control agents introduced from Pakistan, Kenya, South Africa and India have achieved limited success. The search for gall-inducing agents was shifted to East and West Africa and a gall thrips (Acaciothrips ebneri) from Ethiopia was selected for host specificity testing based on its potential impacts and observed field host range. The life cycle of A. ebneri is completed within the developing galls after approximately one month. Adults are 1-2mm and live up to 4 months. The gall thrips was approved for field release in Australia in late 2022, the first gall insect to be approved and released for biological control of prickly acacia in Australia. Mass-rearing and field release of gall thrips commenced in January 2023 with field releases and monitoring continuing across sites along inland and coastal areas in Queensland. Field establishment and dispersal of the gall thrips have been confirmed at most released sites. Glasshouse trials assessing the impact of gall thrips on prickly acacia juvenile plants have indicated the gall thrips can significantly reduce shoot growth and biomass. A new redistribution program will start in 2026 to expand the impact of the gall thrips as quickly and efficiently as possible in Australia.