Host Selection and Host Range of the Flower-Feeding Weevil,Coelocephalapion pigrae,a Potential Biological Control Agent ofMimosa pigra

We studied selection of plant parts, selection of host plant species, and selection in relation to damage, by the weevilCoelocephalapion pigraeKissinger (Coleoptera, Apionidae), a potential biological control agent of the weedMimosa pigraL. (Mimosaceae). Adults fed on flower buds of all developmental stages and on growing leaves but oviposited only in flower buds mainly at mid to late stages of development. Larvae developed and pupated within flowers both before and after opening. In choice tests, adults preferredM. pigrafor oviposition and feeding. Occasional oviposition occurred on the weed,Mimosa pudica,and on the native plant,Neptunia dimorphantha.Some feeding occurred on flowers and/or leaves of 31 other species, mainly in the Mimosaceae. In no-choice tests, the level of oviposition onM. pudicaandN. dimorphanthawas greater than in choice tests but was still less than that onM. pigra.Development was completed on these three species but survival of immature stages was lower onM. pudicaandN. dimorphanthathan onM. pigra.This, together with their low acceptance for oviposition, indicates that neither plant could sustain populations ofC. pigrae.Furthermore, populations ofN. dimorphanthaare disjunct from current and projected populations ofM. pigra.A supporting study on the effect of previous damage on oviposition behavior byC. pigraewas conducted. The effect of previous insect damage and consequent limitation of oviposition sites was to limit further oviposition. This information was used in the design of choice tests which tested both preference and specificity. The results of these tests were accepted by the regulatory authorities andC. pigraewas released in Australia in May 1994.