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

Abstract

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 theconventional 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 SouthWales, Australia, involving 41 test plantspecies. This result was combined with otherconventional considerations to apply for therelease of D. rufa in South Africa. Theseincluded a multiple choice feeding trial inquarantine in South Africa, during which 10test species from seven genera of South AfricanProteaceae were not accepted for feeding. AllSouth African Proteaceae, except Brabejumstellatifolium, are phylogenetically distinctfrom H. sericea. Also, there are norecords of D. rufa interacting withcommercially important plants in Australia,including commercially cultivated South AfricanProteaceae. Dicomada rufa adult andlarval feeding destroys buds, flowers, smallfruits and succulent shoots. It is expectedthat this damage will supplement that of thetwo seed-feeding biological control agentsalready established in South Africa and furtherreduce the reproductive potential of the weed,particularly that of young plants regeneratingafter fires. Without compromising safety, thefixed plot survey method may also contribute toreducing the time and cost normally associatedwith conventional host specificity testing.