Mortality and life-tables of Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) compared on two host-plant species

The performance of Cactoblastis cactorum (Berg) as a biological control agent of the cactus weeds Opuntia ficus-indica and O. aurantiaca was assessed by compiling life-tables for each host-plant, in both a summer and a winter generation, at a site in South Africa. Egg predation, mostly by ants, ranged from 54 to 74% and was significantly higher on O. aurantiaca than on O. ficus-indica. Larval mortality on O. aurantiaca was high during the summer generation (65%), possibly because of dehydration of cladodes. Survival on O. aurantiaca was 55 and 60% of that on O. ficus-indica in the summer and winter generations, respectively. Adult mortality, calculated from the life-tables, was 45 and 84% in the summer and winter generations, respectively. The most important components of mortality were natural enemies in the summer generation and weather-related factors in the winter generation. Host-plant-related mortality was not as great as was formerly supposed.