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

Gordon, A.J.

Biological control of weeds in South Africa 1990-1998: 35-43


Accession: 003025984

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Hakea sericea, an Australian proteaceous shrub or small tree, has become a major problem in nearly all the coastal mountain ranges and catchments of the southwestern and southern Western Cape Province of South Africa. Biological control was initiated in 1970 and focused largely on the release of insects that reduce seed production. Although the seed-feeding weevil Erytenna consputa and seed-feeding moth Carposina autologa became established, only E. consputa was considered to contribute to the reduction of the seed crop. The shoot-boring weevil Cydmaea binotata, released in 1979 to suppress seedling regeneration, has mostly failed to establish and may only be surviving at one site. In this paper, the biological control programme against H. sericea is reviewed, 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 beetle Aphanasium australe and bud-feeding weevil Dicomada rufa. Erytenna consputa continues to reduce the annual seed crop, especially in the southern Western Cape Province where natural and accidental fires are less frequent. Carposina autologa is considerably more effective than previously thought and populations are thriving at several sites where they were released in the 1990s. Host-specificity tests on A. australe, which also attacks Hakea gibbosa, indicated that the beetle is suitable for release, and permission for its release in South Africa was sought in March 1999. Culturing difficulties with D. rufa precluded host-specificity tests in quarantine, but field evaluations in Australia strongly suggested that the weevil is host specific and an application for permission to release D. rufa are due to be submitted in 1999. The resumption of mechanical clearing operations in catchments invaded by H. sericea has necessitated the establishment of natural enemy 'reserves' to prevent the destruction, and possibly local extinction, of natural enemy populations.