Host-plant affinities of two biotypes of Dactylopius opuntiae (Homoptera: Dactylopiidae):: enhanced prospects for biological control of Opuntia stricta (Cactaceae) in South Africa

1. Until recently, neither the phycitid moth Cactoblastis cactorum nor the cochineal insect Dactylopius opuntiae have been satisfactory biological control agents of Opuntia stricta in South Africa. 2. In marked contrast, both of these agents have kept O. stricta under biological control for many decades in Australia. 3. In an attempt to improve the situation in South Africa, a stock of D. opuntiae was obtained from O. stricta in Australia during 1996. 4. Host-specificity tests confirmed that the newly imported D. opuntiae from Australia is a different biotype to the one already established in South Africa. 5. The Australian ('stricta') biotype thrives on O. stricta but is unable to develop satisfactorily on O. ficus-indica, while the converse is true for the South African ('ficus') biotype, which thrives on O. ficus-indica but fares poorly on O. stricta. 6. The integrity of the host-plant specificity of the two biotypes of D. opuntiae has important implications for biological control of Cactaceae in South Africa, and has greatly enhanced prospects that O. stricta can be brought under biological control successfully.