Print PageCactoblastis cactorum (Lepidoptera: Pyralidae), the cactus moth, is both an effective biological control agent and an invasive pest of opuntioid cacti. The continuing spread of Cactoblastis in the southeastern United States threatens opuntioid species, which play an important role in the biological and physical integrity of desert, scrub, and coastal habitats. We performed a six-year census of marked Opuntia stricta (n=253) and Opuntia humifusa (n=327) plants along the west central coast of Florida to determine the following: 1) Are plants attacked by Cactoblastis more likely to die than non-attacked plants? 2) How does rate of Cactoblastis attack affect survival of plants? 3) For surviving plants, does Cactoblastis attack affect growth rate? 4) Do the two Opuntia species differ in their Cactoblastis attack rates and response to attack?
Results/Conclusions
78.11% of the Opuntia plants were attacked at least once by Cactoblastis during the six year study; overall survival rate was 75.8%. We found that plants attacked by Cactoblastis were more likely to die than non-attacked plants and that a plant’s odds of surviving the six year period decreased as Cactoblastis attack rate increased. Plants that survived the six year period showed, on average, positive growth. There was no significant difference in growth rates between plants attacked by Cactoblastis and non-attacked plants. O. stricta plants were more likely to be attacked by Cactoblastis, had a significantly higher attack rate, and were more likely to die after being attacked than were O. humifusa plants. Our results indicate than although Cactoblastis can decrease the survival of Opuntia plants, overall survival along the west central coast of Florida is still high. Surprisingly, plants that were able to survive Cactoblastis attack did not show a reduction in growth rate, suggesting that survivors may possess traits that render them tolerant to Cactoblastis attack.
