Integrated management of Opuntia stricta (Haworth) Haworth (Cactaceae) in South Africa: an enhanced role for two, renowned, insect agents

The increasing importance of Opuntia stricta (Haworth) Haworth (Cactaceae) as an invasive weed in many parts of South Africa has resulted in the initi ation of a biological control campaign against the weed. Two herbivorous in sect species, Cactoblastis cactorum (Bergroth) (Lepidoptera: Phycitidae) an d Dactylopius opuntiae (Cockerell) (Homoptera: Dactylopiidae) have attacked O. stricta in South Africa since their successful introduction into the co untry during the 1930s for biological control of a related weed species, Op untia ficus-indica (L.) Miller. Both C. cactorum and D. opuntiae played a c entral role in the highly successful biological control campaign against O. stricta in Australia, but neither species has been effective on O. stricta in South Africa. Predation seems to have prevented C. cactorum from becomi ng abundant enough to have a major impact on the weed and the biotype of D. opuntiae initially introduced into South Africa for O. ficus-indica perfor ms poorly on O. stricta. The efficacy of the biological control programme a gainst O. stricta has been enhanced by: (i) the development of integrated c ontrol procedures which use herbicides together with C. cactorum, and (ii) the introduction of a different biotype of D. opuntiae that is compatible w ith O. stricta.