Survey and prioritisation of potential biological control agents for prickly acacia (Acacia nilotica subsp. indica) in southern India

Abstract

Prickly acacia, Acacia nilotica subsp. indica (Benth.) Brenan (Mimosaceae), a multi-purpose tree native to the Indian subcontinent, is a weed of national significance, widespread throughout the grazing areas of western Queensland and has the potential to spread throughout northern Australia. Biological control of prickly acacia 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 64 sites in Tamil Nadu state and eight sites in Karnataka state from November 2008 to December 2011. Surveys yielded 33 species of phytophagous insects (16 species of leaf-feeders, eight species of stem feeders, four species with leaf-feeding adults and root-feeding larvae, two stem-borers and bark-feeders and three flower-feeders) and two rust fungi. The number of species recorded at survey sites increased with the number of times the sites were surveyed. Using a scoring system based on field host range, geographic range, seasonal incidence and damage levels, we prioritised a scale insect (Anomalococcus indicus Ramakrishna Ayyar), two leaf-webbing caterpillars (Phycita sp. A and Phycita sp. B), a leaf weevil (Dereodus denticollis Boheman), a leaf beetle (Pachnephorus sp.), a gall-inducing rust (Ravenelia acacia-arabica Mundk. & Thirumalachari) and a leaf rust (Ravenelia evansii Syd. & P.) for detailed host specificity tests. The two rusts were sent to CABI-UK for preliminary host-specificity testing. Three insects (A. indicus, D. denticollis and Phycita sp. A) were imported into a quarantine facility in Brisbane, Australia where host-specificity tests are in progress.

Keywords:

• native range survey
• agent prioritisation
• field host range
• Acacia nilotica
• India
• Australia

Acknowledgements

The authors thank M. Senthilkumar, Mrs Mahalakshimi (Institute of Forest Genetics and Tree Breeding, Coimbatore, Tamil Nadu, India), Syed Irfan Ahmed, Sangeeta Singh, K.K. Srivastava, Mahadeo Gorin and Anamika Sharma (Arid Forest Research Institute, Jodhpur, Rajasthan, India) for the field surveys; N. Krishnakumar (Director, IFGTB, Coimbatore, India) and T.S. Rathore (Director, AFRI, Jodhpur, India) for the facilities; Bill Palmer, S. Raghu and Dane Panetta for comments on earlier versions of the manuscript; and Meat & Livestock Australia for funding the study. They also thank the Indian Council of Forestry Research and Education for providing permission to run this collaborative research project in India. They are grateful to V.V. Ramamurthy (Indian Agricultural Research Institute, New Delhi), Mathew George (Kerala Forest Research Institute, India), S.K. Gupta (Zoological Survey of India, Kolkata); Thomas Simonsen, Kevin Tuck Marion, John Chainey, Sharon Shute (British Natural History Museum); Marion Seier, Harry Evans (CABI, UK); Laurence Mound (CSIRO Entomology, Canberra) for identification of various insects, mites and rust species collected during this study.