Biological control initiatives against the invasive Oriental legume, Caesalpinia decapetala (Roth) Alston (Mauritius thorn), in South Africa

Caesalpinia decapetala (Roth) Alston, a woody legume reported to be of Orie ntal origin, is an aggressive invader of riverine habitats, forest margins and clearings, grasslands and commercial plantations in South Africa. Mecha nical and chemical control methods are impractical and ineffective, and her bicides are often undesirable because of the risk of water pollution. Biolo gical control could therefore play an important part in the suppression of this weed. Mauritius thorn is cultivated as a barrier plant in South Africa but many indigenous plants can be used for this purpose, so no conflicts o f interest are envisaged. Preliminary surveys for natural enemies in India revealed a depauperate insect fauna, suggesting that future surveys should focus on other Asian regions. Two insect species have been introduced from India into quarantine in South Africa. Oviposition choice-tests in quaranti ne demonstrated that the seed-feeding beetle Sulcobruchus bakeri Kingsolver (Bruchidae) has a strong preference for ovipositing on C. decapetala seeds . Sulcobruchus bakeri was cleared for release in South Africa in February 1 999. A culture of the leaf-mining moth Acrocercops hyphantica Meyr. (Gracil lariidae) was established in quarantine in November 1998. Biology studies a nd host-range tests on A. hyphantica are in progress.