ARS | Publication request: Regarding the role of new host associations in the success of Cactoblastis cactorum as both a biological control agent and invasive species.

Submitted to: International Symposium on Biological Control of Weeds
Publication Type: Proceedings
Publication Acceptance Date: June 27, 2011
Publication Date: N/A

Technical Abstract: A key theoretical basis for using classic biological control against invasive alien species (IAS) has been the enemy release hypothesis (ERH), which suggests that the increased vigor and invasiveness of IAS in the introduced range is strongly influenced by their release from co-evolved natural enemies. Classical biological control aims to reunite IAS with their natural enemies and restore ecological balance and stability. The ERH is supported by the historical example of highly-invasive Opuntia spp. in Australia that had been introduced from North America without their natural enemies. It also is supported by the legendary control of these invasive Opuntia spp. when the herbivore, Cactoblastis cactorum, was introduced from Argentina without its natural enemies. Cactoblastis cactorum later was unintentionally introduced into Florida where it has rapidly expanded its geographical range along both the Atlantic and Gulf of Mexico coasts, invaded the Yucatan Peninsula, Mexico, and threatens Opuntia-based agriculture and ecosystems in the southwestern USA and Mexico. Although the ERH predicts that classical biological control would be indicated for this invasive pest, we wanted to examine the role of all mortality factors in the native range using life table analysis on both native, co-evolved Opuntia host species and on an introduced, non-co-evolved Opuntia host species. We found limited egg and larval mortality due to predators or parasitoids, however there was a strong influence of co-evolved host plant resistance by the native Opuntia spp. Larval establishment, rate of larval development, and number of generations per year were lower on the native Opuntia spp. than on the introduced Opuntia species. Although the ERH may be a factor in the success of C. cactorum as both a biological control agent and an invasive species, results from our studies in its native range suggest that release from co-evolved host plant resistance may exert a greater influence.