Defining ecotypic variation in the invasive moth, Cactoblastis cactorum (Berg), and its implication for spread in North America

The cost of controlling the spread of invasive species is exorbitant – with estimates of the annual cost of control exceeding the budget of the Department of Homeland Security. Exotic insect herbivores are especially problematic because their hosts are frequently agricultural crops whose damage is also very costly. Understanding the mechanisms that govern successful invasion and spread of these exotic herbivores is critical to devising effective control measures. Escaped biological control organisms such as the South American Cactus Moth, Cactoblastis cactorum (Berg), provide excellent opportunities to explore these mechanisms. Here we describe the ecotypic variation in C. cactorum across its native range and part of its exotic range (Florida, U.S.A.) using statistical analysis of data on geographic patterns of genetic isolation, larval morphology and host association. The fact that all exported individuals used as biocontrol are from a single collection made from a single ecotype suggests the potential importance of this ecotypic variation on invasion success. Biases in host use are apparent for each ecotype and provide the most information for assigning samples to the correct ecotypic group. Continued specialization of invasive insects on a subset of available hosts in the exotic range suggests that this bias in host association is fundamental to understanding future spread of the moth.