Background/Question/Methods

Cactoblastis cactorum (Lepidoptera: Pyralidae), the cactus moth, is a well-known biological control agent for cactus species of the genus Opuntia. The arrival of the moth in Florida and its subsequent spread through the southeastern United States pose a threat to opuntioid diversity in North America. Of particular concern are the ecological and economic impacts the moth could have in the cacti-rich southwestern U.S. and Mexico, where both native and cultivated Opuntia species are important resources.  Although C. cactorum is considered oligophagous, it is unknown which species would be preferred by ovipositing females or would best support larval development if the moth were to spread to the southwestern U.S. and Mexico. The objectives of this study were to 1) determine if ovipositing females would demonstrate a preference for any of fourteen opuntioid species native to Mexico, the Caribbean, and the southwestern U.S. and 2) determine which of the same fourteen species would best support larval development. The species used were: Consolea rubescens, Cylindropuntia acanthocarpa, Cylindropuntia spinosior, Nopalea cochenillifera, Opuntia dillenii, O. engelmannii, O. engelmannii var. lindheimeri, O. engelmannii var. linguiformis, O. ficus-indica, O. leucotricha, O. macrocentra, O. microdasys, O. santa-rita, and O. streptacantha. In order to test for oviposition preference, we used a common garden experiment and recorded numbers of eggsticks laid by wild moths over the course of one year. We then examined larval development from eggstick to adult in no-choice experiments.

Results/Conclusions

Preliminary results show that females preferred O. engelmannii var. linguiformis as an oviposition site; trends also showed a preference for O. engelmannii, O. dillenii, and O. santa-rita.  Both pupation rate and adult emergence rate were highest on Consolea rubescens. Despite being preferred by females, O. engelmannii var. linguiformis was not a good host for C. cactorum, with less than seven percent of larvae surviving to the adult stage. The number of developed eggs upon emergence did not differ significantly among those species that produced females; however, five species (O. engelmannii var. lindheimeri, O. macrocentra, O. microdasys, Cylindropuntia acanthocarpa, and Cylindropuntia spinosior) produced no adults or only males. Cuticle toughness was found to be a significant predictor of pupation rate, but not of other larval performance parameters. This study aims to provide information on those species that will be most at risk from C. cactorum in the event of its invasion into the opuntioid diversity “hot spots” of North America.