New biocontrol opportunities for prickly acacia: exploration in India

Abstract

Prickly acacia (Vachellia nilotica ssp. indica), a multipurpose tree native to the Indian subcontinent, is a Weed of National Significance and is widespread throughout the grazing areas of northern Australia. Biological control of V. nilotica ssp. indica has been in progress since the early 1980s, but with limited success to date. Based on genetic and climate matching studies, native surveys for potential biological control agents were conducted in India during 2008-2011. A total of 72 sites were surveyed in southern India and 60 sites in north-western India. Surveys yielded 33 species of phytophagous insects and two rust fungi. Based on host records, 20 insect species that are crop pests or polyphagous, and all plant pathogens other than the two rust fungi, were excluded from the list of potential biological control agents. Using field host range, geographic range, seasonal incidence, damage potential, and preliminary host-specificity test results in India, as filters, the following agents were prioritised for detailed host specificity tests: a scale insect (Anomalococcus indicus), two leaf-webbers (Phycita sp. A and Phycita sp. B), a leaf weevil (Dereodus denticollis), a leaf beetle (Pachnephorus sp.), one gall-inducing rust (Ravenelia acacia-arabicae) and a leaf rust (Ravenelia evansii). The two rusts were sent to CABI-UK for preliminary host-specificity testing. Import permits for the brown leaf-webber (Phycita sp. A), the green leaf-webber (Phycita sp. B), the scale insect (A. indicus), the leaf-weevil (D. denticollis) and the leaf-beetle (Pachnephorus sp.) have been obtained from relevant regulatory authorities in Australia. So far, 11 importations, containing several thousands of insects in total have been exported from India into a quarantine facility in Brisbane, Australia. Based on these importations, host specificity tests for the brown leaf-webber (Phycita sp. A) have been completed, and the tests for the scale insect (A. indicus) and the green leaf-webber (Phycita sp., B) are in progress. Additional importations of the leaf-weevil (D. denticollis) and the leaf-beetle (Pachnephorus sp.) are planned for later in the year, when conditions are more conducive for field collections.