THE HOST SPECIFICITY OF RHOPALOMYIA-CALIFORNICA FELT (DIPTERA, CECIDOMYIIDAE) AND ITS IMPORTATION INTO AUSTRALIA AS A BIOLOGICAL-CONTROL AGENT FOR BACCHARIS-HALIMIFOLIA L

The cecidomyiid gallformer Rhopalomyia californica Felt is endemic to California where its natural host is Baccharis pilularis. The midge also develops in B. halimifolia and B. neglecta in the laboratory and this made it a potential biocontrol agent for B. halimifolia, a serious weed in Australia. Host specificity tests indicated that the flies would not oviposit on any of 65 economically important plant species. It was therefore considered safe for introduction into Australia. After two unsuccessful attempts, establishment was achieved in Queensland in 1982. A subsequent large scale mass rearing and releasing effort resulted in the insect being established throughout the range of B. halimifolia in Australia by 1986. The insect has given a measure of control particularly in elevated areas and in years when spring and early summer were wetter and cooler.