A review of established and new insect agents for the biological control of Hakea sericea Schrader (Proteaceae) in South Africa

Hakea sericea Schrader, an Australian proteaceous shrub or small tree, has become a major problem in nearly all the coastal mountain ranges and catchm ents of the southwestern and southern Western Cape Province. Biological con trol was initiated in 1970 and focussed largely on the release of insects t hat reduce seed production. Although the seed-feeding weevil Erytenna consp uta Pascoe and seed-feeding moth Carposina autologa Meyrick became establis hed, only E. consputa was considered to contribute to the reduction of the seed crop. The shoot-boring weevil Cydmaea binotata Lea, released in 1979 t o suppress seedling regeneration, has mostly failed to establish and may on ly be surviving at one site. In this paper I review the biological control programme against H. sericea, focussing on the initiatives undertaken since 1990, which included (i) the redistribution of C. autologa and evaluations on its efficacy and (ii) host-specificity evaluations on the stem-boring b eetle Aphanasium australe (Boisduval) and bud-feeding weevil Dicomada rufa Blackburn. Erytenna consputa continues to reduce the annual seed crop, espe cially in the southern Western Cape Province where natural and accidental f ires are less frequent. Carposina autologa is considerably more effective t han previously thought and populations are thriving at several sites where they were released in the 1990s. Host-specificity tests on A. australe, whi ch also attacks Hakea gibbosa (Sm.) Cav., indicated that the beetle is suit able for release, and permission for its release in South Africa was sought in March 1999. Culturing difficulties with D. rufa precluded host-specific ity tests in quarantine, but field evaluations in Australia strongly sugges ted that the weevil is host specific and an application for permission to r elease D. rufa will be submitted in 1999. The resumption of mechanical clea ring operations in catchments invaded by H. sericea has necessitated the es tablishment of natural enemy 'reserves' to prevent the destruction, and pos sibly local extinction, of natural enemy populations.