Rearing and release of Homichloda barkeri (Jacoby) (Coleoptera: Chrysomelidae: Alticinae) for the biological control of prickly acacia, Acacia nilotica ssp. indica (Mimosaceae) in Australia

Abstract

Prickly acacia, Acacia nilotica ssp. indica, a major weed of the Mitchell Grass Downs of northern Queensland, has been the target of biological control projects since the 1980s. The striped leaf-feeding beetle, Homichloda barkeri (Coleoptera: Chrysomelidae: Alticinae), was the third insect approved for release for the control of this weed in Australia. However, mass rearing this insect under glasshouse conditions proved to be difficult and time consuming as there were problems associated with low egg-hatching rates and poor larval survival. Eggs in diapause were stimulated to hatch by repeated wetting and drying. Larvae were fed on potted prickly acacia plants in cages. Late-instar larvae were collected and transferred to a mix of sand, peat moss and vermiculite for pupation and adult emergence. Over 10 500 adults were released at 28 sites in north Queensland between November 1996 and December 1999. Initial releases of insects confined to gauze cages resulted in limited adult survival, oviposition and development of first-generation larvae. First-generation larvae were observed at two sites where cages were not used. However, later inspections of release sites, including those made in April and December 2000, April 2001 and late March 2002, failed to find any trace of the insect, which is assumed to have failed to establish. Possible reasons for this failure are discussed.