Control and persistence of native Opuntia on Nevis and St. Kitts 50 years after the introduction of Cactoblastis cactorum

Since Cactoblastis cactorum appeared in Florida in 1989, via importation of infested horticultural Opuntia plants and/or natural spread from the Caribbean, there has been a concern about the moth's threat to native and economic North American and Mexican Opuntia. The moth's occurrence in the Caribbean is due to its introduction to Nevis Island in 1957 for the control of native Opuntia that were pasture weeds. We assessed the abundance of C. cactorum in target and non-target Opuntia species and the persistence of these Opuntia species on the small islands of Nevis and St. Kitts 50 years after the moth's introduction. C. cactorum occurred at 10/16 sites on the two islands and attacked 22.7% of total plants. Of the four Opuntia sensu lato species found, three were attacked, including the native targets Opuntia triacantha (with 15.6% of plants and 8.9% of pads attacked) and Opuntia stricta (with 44.4% plants and 8.1% pads attacked), and the non-target cultivated and naturalized Opuntia cochenillifera (with 19.1% plants and 1.2% pads attacked). The native nontarget tree pear, Consolea (= Opuntia) rubesens, was not attacked. Larger and wild plants had significantly higher percentages of attack. Based upon our data, it appears that biological control of O. triacantha and O. stricta persists and these natives have survived 50 years of C. cactorum attack on these small islands, despite fears that the moth could have caused their extinction. Our analysis of this historical biological control effort suggests that the potential impact of C. cactorum on Dative North American and Mexican Opuntia will be significant and variable, but not necessarily catastrophic.