Should the flower bud weevil Anthonomus santacruzi (Coleoptera: Curculionidae) be considered for release against the invasive tree Solanum mauritianum (Solanaceae) in New Zealand?

Abstract

The invasive tree Solanum mauritianum Scop. has been targeted for biological control in South Africa and New Zealand, by deploying insect agents that could constrain its excessive reproductive output. The flower-feeding weevil Anthonomus santacruzi (Curculionidae) was approved for release in South Africa in 2007 but following the loss of the original culture in quarantine, new stocks were introduced from Argentina in 2008–2009. This study was initiated to confirm that the host range of the new culture was the same as that of the previous one, but also to assess the risks associated with the weevil's release in New Zealand. Different testing procedures, including no-choice tests and multi-choice tests in different arenas, produced inconsistent and ambiguous results. During no-choice tests, oviposition and larval development to adulthood occurred on three non-target species including two native South African and one native New Zealand Solanum species. However, subsequent multi-choice tests and a risk assessment suggested that the risks of anything more than collateral damage to non-target Solanum species are low. Overall, these data do not deviate substantially from the results of the original quarantine tests which facilitated the release of A. santacruzi in South Africa in 2009. Although we argue that none of the New Zealand native and cultivated species are at risk, stronger evidence from open-field trials and chemical ecology studies may be required to convince the regulatory authorities that A. santacruzi is suitable for release in New Zealand.