Anthonomus santacruzi Hustache (Curculionidae), a new biological control agent for bugweed, Solanum mauritianum Scopoli, in South Africa, poses no risks to cotton production

Abstract

Management of the invasive South American tree, Solanum mauritianum Scopoli (Solanaceae) (bugweed, woolly nightshade), in South Africa will be greatly enhanced by the establishment of florivorous agents that reduce the weed’s excessive levels of fruiting (Olckers 1999). The flowerbud-feeding weevil, Anthonomus santacruzi Hustache (Curculionidae), was proposed for release in South Africa in 2003, based on host records and observations in its native range and on four years of host-specificity testing in quarantine in South Africa (Olckers 2003). During the review process, the South African cotton industry expressed concerns about possible risks posed by the weevil to cotton production (S.W. Broodryk, pers. comm.). This was because a related species, Anthonomus grandis Boheman (boll weevil), constitutes a major pest of cotton, Gossypium hirsutum L., (Malvaceae), in the Americas, but does not occur in South Africa and thus has a high quarantine priority. Earlier host-specificity tests were focussed on plants in the family Solanaceae and did not include cotton, since A. santacruzi and A. grandis are reportedly restricted to host plants in the families Solanaceae and Malvaceae, respectively (Cross et al. 1975; Clark & Burke 1996). As a precaution, the cotton industry requested that two non-transgenic cultivars (i.e. susceptible to insect pests in general) be tested to confirm that the crop is not susceptible to A. santacruzi. This paper discusses the results of these additional trials and their implications for the release of A. santacruzi in South Africa.