PROC. ENTOMOL. SOC. WASH. 95(1), 1993, pp. 1-6 THE HOST SPECIFICITY OF RHOPALOMYIA CALIFORNICA FELT (DIPTERA: CECIDOMYIIDAE) AND ITS IMPORTATION INTO AUSTRALIA AS A BIOLOGICAL CONTROL AGENT FOR BACCHARIS HALIMIFOLIA L. W. A. Palmer, G. Diatloff, and J. Melksham (WAP) North American Field Station, Queensland Department of Lands, 2801 Arrow-head Circle, Temple, Texas 76502; (GD & JM) Alan Fletcher Research Station, Queens-land Department of Lands, 27 Magazine Street, Sherwood, Queensland 4075, Australia. Abstract.— ThQ cecidomyiid gallformer Rhopalomyia californica Felt is endemic to Cal-ifornia where its natural host is Baccharis pilularis. The midge also develops in B. hal-imifolia 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, estab-lishment 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. hal-imifolia 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. Key Words: Biological control, Cecidomyiidae, gall, Rhopalomyia, Baccharis The North American woody shrub Bac-charis halimifolia L. (Family Asteraceae: Tribe Astereae: Sub-Tribe Baccharidinae) is a noxious weed in Queensland and New South Wales, Australia, and is the target of an extensive program to find suitable bio-logical control agents. This program has in-volved searches in both South America (McFadyen 1979) which is the ancestral home of the genus, and North America (Palmer 1987, Palmer and Bennett 1988) where 20 species, including B. halimifolia, are native (Mahler and Waterfall 1964). In North America, three species (B. hal-imifolia, B. neglecta Britton, and B. pilularis DC) are apparently phytochemically very similar because a number of stenophagous insects accept all three as hosts under lab-oratory conditions (Palmer 1986, Palmer and Tilden 1988, Palmer 1989). Recently, Nesom (1990) placed these three species in the same section, Baccharis, of the genus. It was therefore considered that the insect fauna on B. pilularis might provide useful biological control agents for B. halimifolia. One such insect was the gall midge Rho-palomyia californica Felt (Diptera: Ceci-domyiidae) which develops in multi-cham-bered galls on B. pilularis in California and which is one of at least seven species of cecidomyiidae that utilize Baccharis spp. in North America (Gagne 1989). This paper describes the host testing procedures and the subsequent successful introduction of this insect into Australia. Biology and Ecology The biology of R. californica was de-scribed by Tilden (1951) and McFadyen (1985). Briefly, adults emerge from the gall
The host specificity of Rhopalomyia california felt (Diptera: Cecidomyiidae) and its importation into Australia as a biological control agent for Baccharis halimifolia L
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