Prospects for the classical biological control of Calotropis procera (Apocynaceae) using coevolved insects

Abstract

Calotropis procera (Apocynaceae), a native of tropical Africa, the Middle East and the Indian subcontinent, is a serious environmental and rangeland weed of Australia and Brazil. It is also a weed in Hawaii in the USA, the Caribbean Islands, the Seychelles, Mexico, Thailand, Vietnam and many Pacific Islands. In the native range C. procera has many natural enemies, thus classical biological control could be the most cost-effective option for its long-term management. Based on field surveys in India and a literature search, some 65 species of insects and 5 species of mites have been documented on C. procera and another congeneric-invador C. gigantea in the native range. All the leaf-feeding and stem-boring agents recorded on Calotropis spp. have wide host range. Three pre-dispersal seed predators, the Aak weevil Paramecops farinosus, the Aak fruit fly Dacus persicus in the Indian subcontinent and the Sodom apple fruit fly Dacus longistylus in the Middle East, have been identified as prospective biological control agents based on their field host range. In Australia and Brazil, where C. procera has the potential to spread across vast areas, pre-dispersal seed predators would help to limit the spread of the weed. While the fruits of C. procera vary in size and shape across its range, those from India are similar to the ones in Australia and Brazil. Hence, seed-feeding insects from India are more likely to be suitable due to adaptation to fruit size and morphology. Future survey efforts for potential biological control agents should focus on North Africa.

Keywords:

• native range survey
• weed
• calotrope
• rubber bush
• Sodom apple

Acknowledgements

I thank A. Balu, M. Murugesan, P. Senthikumar (Institute of Forest Genetics and Tree Breeding, India) and Anamika Sharma (Arid Forest Research Institute, India) for help with field surveys and identification of natural enemies in India; Asad Shabbir (University of Punjab, Pakistan), Sushil Kumar (Directorate of Weed Science Research, India), Kailash Chandra (Zoological Survey of India), Arne Witt (CABI-Africa), Shane Campbell and Kelli Pukallus (Tropical Weeds Research Centre, Charters Towers, Australia) for providing information on insects associated with Calotropis spp. and V.V. Ramamurthy (Indian Agricultural Research Institute), C. A. Viraktamath (University of Agricultural Sciences, Bangalore) and Owen Seeman (Queensland Museum, Australia) for the identification of insects and mites. I thank Shane Campbell, Bill Palmer, Tony Pople, Joe Scanlan and the anonymous reviewers for comments on earlier drafts of the manuscript.