The fixed plot survey method for determining the host range of the flowerbud-feeding weevil Dicomada rufa, a candidate for the biological control of Hakea sericea in South Africa

摘要

The hakea bud weevil, Dicomada rufa (Curculionidae), is a promising candidate for the biological control of the weed Hakea sericea (Proteaceae) in South Africa. Because D. rufa could not be successfully cultured on potted plants in quarantine, most of the conventional methods for host range determination were not suitable. A type of open-field testing method, the fixed plot survey method, was developed to show that D. rufa is host specific to H. sericea. The trial was conducted in three 1-2 ha plots at three localities in New South Wales, Australia, involving 41 test plant species. This result was combined with other conventional considerations to apply for the release of D. rufa in South Africa. These included a multiple choice feeding trial in quarantine in South Africa, during which 10 test species from seven genera of South African Proteaceae were not accepted for feeding. All South African Proteaceae, except Brabejum stellatifolium, are phylogenetically distinct from H. sericea. Also, there are no records of D. rufa interacting with commercially important plants in Australia, including commercially cultivated South African Proteaceae. Dicomada rufa adult and larval feeding destroys buds, flowers, small fruits and succulent shoots. It is expected that this damage will supplement that of the two seed-feeding biological control agents already established in South Africa and further reduce the reproductive potential of the weed, particularly that of young plants regenerating after fires. Without compromising safety, the fixed plot survey method may also contribute to reducing the time and cost normally associated with conventional host specificity testing.