Biology and climatic requirements of Perapion antiquum (Coleoptera: Apionidae) in southern Africa: implications for the biological control of Emexspp. in Australia

The potential distribution of the South African weevil, Perapion antiquum (Gyllenhal), a biological control agent for the weeds Emex spp., was deter mined by the computer program CLIMEX, using its native distribution, phenology and abundance together with development parameters. The predicted distribution included parts of Hawaii where the weevil successfully controlled Emex australis and E. spinosa. In Australia, sites of past unsuccessful releases have climates that this analysis indicates are unsuitable for the insect. The most favourable regions for establishment of the weevil are near the coast in the southern half of Australia, but most of these do not overlap with regions where Emex spp. are a problem. In western Cape Province, South Africa, E. australis plants are abundant and the weevil attacks the plant after seeds have formed. In Hawaii, a fortuitous combination of climatic conditions favours the weevil during the period after seed germination, and this may be the key to its control of the weed. Sites with climatic conditions similar to successful control sites in Hawaii are not found in Australia. It was concluded that P. antiquum will be of limited use as a biological control agent in Australia even in areas suitable for its establishment.