Control of invasive prickly pear cacti, Opuntia spp. (Cactaceae), by the cactus moth, Cactoblastis cactorum Berg (Lepidoptera: Pyralidae), is often cited as a classic example of successful biological control (Dodd 1940, Moran & Zimmermann 1984). However, the unintentional arrival of C. cactorum in Florida (Habeck & Bennett 1990) raised concerns for the safety of native and rare Opuntia in the Florida Keys and for the potential spread of C. cactorum to Opuntia-rich areas of the western USA and Mexico. In addition to threatening cactus agriculture in the region and the biodiversity of native ecosystems, the negative publicity on such a well-known biological control agent could dampen public support for future weed biological control programs. In September 2000, a workshop was convened to evaluate the potential impact of C. cactorum in North America. The workshop proceedings, published in the Florida Entomologist (Dec. 2001 Volume 84), provide a thorough review of the subject.
The first record of C. cactorum in North America was from Big Pine Key, FL, in October 1989 (Habeck & Bennett 1990). Over the next decade the insect spread north along both Florida coasts (Johnson & Stiling 1998) and by 2000 was detected at Cedar Key along the Gulf Coast and at Sapelo Island, GA, along the Atlantic Coast (Fig. 1). It was not present at Horseshoe Point, Piney Point or Keaton Beach in September 2000. Colonization of Opuntia spp. in the Florida interior has been slower than along coastal areas, although infestations around Orlando in Orange and Osceola Counties have been reported (Fig. 1).
Surveys for larval damage and egg sticks along the Atlantic and Gulf Coasts were conducted in 2001 to improve our knowledge of the distribution of C. cactorum and to delimit the leading edge of its expanding range (Fig. 1). Numerous plants of O. stricta (Haw.) Haworth and O. pusilla (Haworth) Nuttal were sampled in Florida at St. Marks National Wildlife Refuge, Dekel Beach, Keaton Beach and Steinhatchee in March 2001. No C. cactorum were found; however, a native cactus moth, Melitara prodenialis Walker (Lepidoptera: Pyralidae), was found infesting both species at all locations except St. Marks. In July 2001, O. stricta cacti were sampled at Big Lagoon State Recreation Area, Perdido Key, Pensacola, Destin, Panama City Beach, St. George Island, St. Marks, Adams Beach, Dekel Beach and Keaton Beach. No C. cactorum were found, but M. prodenialis larvae were present in large numbers at St. George Island and St. Marks. Surveys also were conducted at Jekyll and Tybee Islands, GA, and Hilton Head Island, SC. Opuntia stricta and O. pusilla throughout Jekyll Island and along the causeway connecting the island to the mainland were heavily infested with C. cactorum and to a lesser extent with M. prodenialis. Opuntia stricta on Tybee Island also were found infested with C. cactorum. No C. cactorum were detected on Hilton Head Island. Further surveys in August 2001 at Hilton Head, Kiawah Island, Charleston and Myrtle Beach revealed no C. cactorum.
These locations were surveyed again in 2002 and the search expanded to include areas north of Savannah, GA, along the Atlantic Coast and areas west of Cedar Key, FL, along the Gulf Coast (Fig. 1). In addition, virgin female-baited sticky traps (Pherocon 1-C) were deployed in selected areas to supplement survey efforts in areas with low population densities. Cactoblastis cactorum was detected as far north as Folly Island, near Charleston, SC. Larvae were collected from O. stricta, O. pusilla, O. humifusa (Raf.) Rafinesque and O. ficus-indica (L.) Miller on the South Carolina Islands of Hunting, Edisto and Folly. No C. cactorum were found at locations north of Charleston (Bull Island, Pawleys Island, Huntington Beach, Surfside Beach and Myrtle Beach), although M. prodenialis was collected at all locations. Surveys in 2002 of previously uninfested sites along the Gulf Coast identified the presence of C. cactorum on O. stricta at Keaton Beach and St. Marks. Additional westward surveys found C. cactorum established at St. George Island.
In Florida, C. cactorum threatens one of the rarest plants in North America, Opuntia corallicola (Small) Werderm., a species endemic to the Florida Keys (Austin et al. 1998). By the time C. cactorum was detected in Florida only one small population of 13 mature O. corallicola was known to exist at Little Torch Key (Gordon & Kubisiak 1998). By 1990 several plants were infested with C. cactorum and one plant was killed (Stiling & Moon 2001). Since that time, the Nature Conservancy’s effort to detect and remove the moth’s egg sticks has enabled this cactus population to persist (Higgins 2001).
The status of O. corallicola brightened in December 2001 when a vigorous population was discovered at Swan Key, 100 miles north of Little Torch Key (Bradley & Woodmansee in press). This population consists of approximately 570 plants, including many of reproductive size. In February 2002, we examined 228 plants to estimate the level of attack by C. cactorum. Twenty-five mature O. stricta growing on Swan Key also were examined. No evidence of C. cactorum frass or larval head capsules was found in either species, even when dead and hollow O. corallicola cladodes were dissected. Future efforts should concentrate on the development of a management plan to monitor the Swan Key O. corallicola population to detect invasion by C. cactorum. Cactoblastis cactorum has been recorded on Key Largo and at Cape Florida on Key Biscayne, 14 miles south and 22 miles north of Swan Key, respectively, as well as on the mainland, which is 5 miles to the west. The absence of C. cactorum at Swan Key suggests some heterogeneity in the moth’s geographic occurrence in southern Florida.
Surveys for C. cactorum will continue along the Atlantic and Gulf Coasts at new and previously visited sites beyond the leading-edge of the infestation, as will surveys to evaluate the spread of the moth to the interior of Florida and adjacent states. Detection of C. cactorum infestations using virgin female-baited sticky traps will also continue. This method was effective at detecting C. cactorum at one site where no larval damage was evident.
Observational surveys and virgin female-baited traps have identified the continued spread of Cactoblastis cactorum from the Florida Keys northward along the Atlantic and Gulf Coasts of the USA. The moth has infested native and ornamental cacti north to Charleston, SC, and west to St. George Island, FL. A newly discovered population of endangered Opuntia corallicola was surveyed in southern Florida and found free of moth infestation.