The Frequency and Strength of Nontarget Effects of Invertebrate Biological Control Agents of Plant Pests and Weeds

Abstract

In 1989, the cactus moth, Cactoblastis cactorum, which had been taken from South America and released around the world to control pestiferous Opuntia cacti on which it feeds, appeared in the Florida Keys. How it got there is uncertain. The moth was introduced into the Caribbean island of Nevis in 1957 and then moved by local authorities to other islands (Tuduri et al. 1971). It then either island hopped, as it had in Hawaii (Tuduri et al. 1971), and jumped from Cuba to the Florida Keys, or was carried inadvertently on ornamental cacti imported into Miami, Florida from pads collected in Hispaniola (Pemberton 1995). However, the moth was not noticed in Miami before it was found in the lower Keys so we tend to favor the natural dispersion explanation. The results of this invasion/introduction were rapid and serious. The moth dispersed 320 miles northward through Florida from 1989 to 1991 to reach Brevard County (Johnson and Stiling 1998). On average, from six sites throughout Florida, over 90% of Opuntia stricta plants with more than 10 pads exhibited feeding damage. In 1997 Cactoblastis was found in the Jacksonville area (Stiling, personal observation). If the moth can survive in Jacksonville, it could move across the Gulf Coast states into Texas and beyond. This prompts concern not only for native Florida cacti but also for cacti native to the rest of the North American continent (especially the Opuntia-rich desert southwest). Rare cacti may be particularly at risk. Opuntia spinosissima, whose entire U.S. population consists of 12 plants in the Florida Keys, is a preferred host of Cactoblastis larvae (Johnson and Stiling 1996). Individuals now exist inside cages designed to protect them from Cactoblastis.