Establishment and increased fitness of the seed-feeding weevil Cissoanthonomus tuberculipennis, a biological control agent for balloon vine Cardiospermum grandiflorum in South Africa.
The ability of introduced species to adapt and proliferate in their areas of introduction is attributed to a complexity of factors and processes. Post-release studies were conducted to ascertain establishment, spread and initial impact of the seed-feeding weevil Cissoanthonomus tuberculipennis, a biological control agent released against balloon vine Cardiospermum grandiflorum in South Africa. CLIMEX was used to identify areas where C. tuberculipennis was likely to establish. Comparison were also made of C. tuberculipennis abundance in its native (Argentina) and introduced (South Africa) ranges to determine its relative fitness in the two regions. The weevil successfully overwintered at 12 of 14 release sites and was thus considered to be established after twelve months. The weevil has spread rapidly from all the established release sites in South Africa, confirming CLIMEX predictions conducted prior to its release. The percentage of seeds damaged by C. tuberculipennis across all study sites in South Africa after 12 months was over two-fold greater than in Argentina. The study suggests that C. tuberculipennis has responded to increased resource availability in South Africa, where there is little competition from co-occurring native lepidopteran species which are scarce on the same food resource.