We examined the association between Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) and its prickly pear host plants (subfamily Opuntioideae) in Florida in order to assess the role of host assemblage diversity in the spread of this invasive South American moth.  We measured the prevalence of C. cactorum infestation in communities varying in prickly pear cactus diversity at 165 sites across Florida.  To explore the potential influence of host diversity on the invasion of C. cactorum, we were particularly interested in addressing the following questions.  First, does host species identity affect the presence and prevalence of C. cactorum in Florida?  Second, what is the effect of host diversity on the presence and prevalence of C. cactorum? Answering these questions will both help to increase our understanding of the fate of cactus species in Florida as well as to make better predictions about the potential invasion of the southwestern United States and Mexico by C. cactorum.

Results/Conclusions

The data suggest that dynamics of the invasion are influenced both by a sampling effect as well as diversity per se.  Cactoblastis cactorum prevalence was highest on Opuntia stricta and O. humifusa var. ammophila in comparison with other host species.  In addition, C. cactorum prevalence was significantly higher when O. stricta was present in the community.  Species evenness and density were not predictive of infestation.  Instead, polycultures were significantly more infested than monocultures, independent of the sampling effect. Future work will seek to clarify whether the observed pattern represents a preference for O. stricta per se or for the coastal environment to which that cactus is largely restricted.