BIOLOGICAL-CONTROL OF OPUNTIA-STRICTA (HAW) HAW VAR STRICTA USING DACTYLOPIUS-OPUNTIAE (COCKERELL) IN AN AREA OF NEW-SOUTH-WALES, AUSTRALIA, WHERE CACTOBLASTIS-CACTORUM (BERG) IS NOT A SUCCESSFUL BIOLOGICAL-CONTROL AGENT

Dactylopius opuntiae reduced an Opuntia stricta var. stricta population in the Central Tablelands of New South Wales, an area where Cactoblastis cactorum has little impact. Cactoblastis cactorum was bivoltine at the experimental site. The proportion of C cactorum eggs hatching and larvae penetrating segments was much greater for the generation commencing between November and January compared with that commencing between February and June. Failure of first instar C. cactorum to establish during the latter generation appeared to prevent C. cactorum from having a significant impact on the cactus population. Dactylopius opuntiae released at the site decreased new growth of O. stricta var. stricta and caused direct damage to segments. This damage led to a decline in the cactus population in the area. The use of D. opuntiae for biological control of O. stricta var. stricta in similar areas is discussed.