BIOLOGY AND HOST-RANGE OF THE GREEN-SEED WEEVIL, SIBINIA-FASTIGIATA, FOR BIOLOGICAL-CONTROL OF MIMOSA-PIGRA

Aspects of the biology and host range of Sibinia fastigiata Clark (Col eoptera: Curculionidae) were studied to assess its safety for release in Australia as a biological control agent of the weed Mimosa pigra L. (Mimosaceae). Larvae feed on the seeds and adults on open flowers of their host. Adults oviposit on to immature seeds 3 mm long oi less and hence seeds of this length and maturity were used in the host range t ests and for rearing. Females are shown to avoid previously attacked s eeds enhancing their effectiveness as seed destroyers. Survival of adu lts was higher wizen provided with open flowers. The host range was de termined using laboratory control-choice oviposition tests on excised plant material and, in the field in the native range, no-choice ovipos ition tests an living plants, surveys of adults on plants, and breedin g of insects from pods of plants of various legume species. The contro l-choice oviposition tests employed a new design in which the control plant alone was offered to the insects followed by a choice of test pl ants species. Other than M. pigra, only one giant species was acceptab le for oviposition, the closely related M. asperata. Larval developmen t also occurs on M. asperata and this host is occasionally used in the field. This insect was approved for release in March 1997.