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 con trol agents of Opuntia stricta in South Africa. 2. In marked contrast, both of these agents have kept O. stricta under biol ogical control for many decades in Australia. 3. In an attempt to improve the situation in South Africa, a stock of D. op untiae was obtained from O. stricta in Australia during 1996. 4. Host-specificity tests confirmed that the newly imported D. opuntiae fro m 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 t o 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. op untiae has important implications for biological control of Cactaceae in So uth Africa, and has greatly enhanced prospects that O. stricta can be broug ht under biological control successfully.