Author
Terence Olckers
olckerst@ukzn.ac.za
University of KwaZulu-Natal
Durban
Coauthors
Daniella Egli, University of KwaZulu-Natal, Durban, South Africa
Abstract
The flowerbud-feeding Anthonomus santacruzi (Curculionidae) is widely established in the warmer regions of South Africa, following its release against Solanum mauritianum (woolly nightshade, Solanaceae) in 2008. The risk of non-target effects was deemed sufficiently low to justify release, despite the weevil’s survival to adulthood in the buds of several non-target native Solanum species in pre-release tests. Over a 12-month period, we assessed the weevil’s host-plant utilization in a rangeland supporting S. mauritianum and five previously tested non-target congeners. We recorded larvae in the buds of two native and one exotic non-target species, but in significantly lower proportions than in S. mauritianum buds. Although we consistently recorded adults and larvae on the native S. dasyphyllum, mean monthly numbers were significantly lower than on S. mauritianum. Similarly, floral exploitation (i.e. buds with larvae) and larval survival to adulthood was significantly higher on S. mauritianum. Exploitation of S. campylacanthum (native) was occasional, but only once off in the case of S. viarum (exotic). Since all sampled non-target plants grew within 8 m of the S. mauritianum controls, our results align with predictions of “spillover damage” that is unlikely to pose a long-term threat. Surveys of isolated non-target Solanum populations will continue to confirm that these are not under threat of “full utilization”.
Keywords
Anthonomus santacruzi
host-plant utilization
non-target effects
post-release evaluation
woolly nightshade
Highlights
Anthonomus santacruzi displayed variable non-target effects on two native and one exotic species
Adult and larval numbers were substantially higher on the target weed
Results align with predictions of spillover damage