Acaciothrips ebneri, a new biological control agent for the invasive prickly acacia (Vachellia nilotica subsp. indica) in Australia

Abstract

Prickly acacia (Vachellia nilotica subsp. indica) was introduced into Australia in the 1890s as a drought resistant species for shade, fodder and ornamental purposes. It has since become invasive, being widespread throughout grazing areas in northern, central, and western Queensland and coastal, semi-arid and arid areas elsewhere in northern Australia. It has been designated as a Weed of National Significance. The plant exhibits a number of negative impacts on local ecosystems and agricultural production. Biological control is the most economically viable management option for prickly acacia in Australia. Six agents have been released for prickly acacia with only two agents, a seed-feeding beetle (Bruchidius sahlbergi) and a leaf-feeding moth (Chiasmia assimilis), have established, and with limited impacts. Native range surveys were directed to Ethiopia and Senegal based on genetic and climatic matching. A gall-inducing thrips (Acaciothrips ebneri) was prioritised from Ethiopia for host specificity testing in Brisbane, Australia where host specificity testing was completed for 59 test plant species. The gall thrips is host specific and has been approved for release by Australian Government. It is the first gall insect released for prickly acacia in Australia. Field releases commenced in January 2023 and are continuing, across sites along inland and coastal areas in Queensland. There are early signs of field establishment, host damage, and dispersal of the gall thrips. Future research will focus on monitoring its establishment, dispersal, and impact on prickly acacia.