BIOLOGICAL-CONTROL OF HAKEA-SERICEA (PROTEACEAE) IN SOUTH-AFRICA

Hakea sericea Schrader is a proteaceous shrub or small tree from southeastern Australia which has become an invasive weed of major importance in South Africa, particularly in the mountain catchments of the Southwestern and Southern Cape Province. Two biological control agents were released in 1970 to try and reduce the vast numbers of seeds produced by this weed. A weevil, Erytenna consputa Pascoe, which attacks the immature fruits, is now widely established and is contributing substantially to the reduction of the seed crop. A moth, Carposina autologa Meyrick, destroys seeds in the mature fruits and, after a prolonged period of releases, has recently established thriving colonies in the field. A second weevil, Cydmaea binotata Lea, which feeds on and develops in succulent vegetative growth, was released in 1979 principally to suppress seedling regeneration. It has established at a few sites. but with little effect. Apart from E. consputa which may be restricting the rate of spread of the plant, the programme has not yet fulfilled its promise, although recent prognoses are encouraging. The history of the programme and possible reasons for its limited successes are reviewed.