The cactus moth, Cactoblastis cactorum is native to northern Argentina and parts of Peru and Paraguay. It was introduced into the Caribbean islands in the 1960’s to control several (native) prickly-pear cactus (Opuntia) species (Simonson 2005).
In 1989 the cactus moth was discovered to have spread to southern Florida. The moth probably entered the United States more than once (Simonsen et al. 2008) - either on winds from nearby Caribbean islands or on imported cactus plants. In the 20 years since, the cactus moth has spread up the peninsula as far north as coastal South Carolina and west along the shore of the Gulf of Mexico. (There are both native prickly pear cacti and ornamental cacti throughout the Southeast.) In 2009, it was detected growing on spoil islands in the swamps of southern Louisiana.
The cactus moth can kill most prickly pear cacti (genus Opuntia), in particular those species that have flat pads. In Florida, the cactus moth has already caused considerable harm to the six species of vulnerable prickly pears (Garrett 2004), three of which are state listed. In some places, 75% of the prickly pear cacti have been attacked by the moth, with small individuals at greatest risk of death from these attacks (Johnson and Stiling 1998, Baker and Stiling 2009). Most of the peninsula from Gainesville south is now infested (USDA APHIS 2009a).
The greatest threat is to the deserts of the American Southwest - from Texas to California - and Mexico. These deserts are home to 114 native species of Opuntia (APHIS 2009b), about 80 of which are flat-padded species vulnerable to the cactus moth (Simonson et al. 2005). In the difficult desert environment, prickly pears are a nutritious and reliable food supply for many wildlife species, including deer, javalina (peccaries), Texas and desert tortoises, spiny iguana, and pollen-feeding insects. Prickly pears provide shelter for packrats - which in turn are eaten by raptors, coyotes, and snakes; and for nesting birds including the cactus wren and curve-billed thrasher. The cacti also are nurse plants, under which other desert plants' seedlings may start life. Finally, the prickly pears' root systems hold the highly erodible soils (Simonson 2005).
The economic consequences of loss of prickly pear cacti will fall most heavily on Mexico, where prickly pears provide food to both people and livestock. Prickly pears are cultivated on some 250,000 ha in Mexico for both the fruits (tunas) and pads (nopales). Fruits and pads are collected from the wild across another 3 million ha (Simonson 2005). An estimated 28,000 people are employed by the prickly pear trade in Mexico, generating an estimated US$50 million in revenue annually during the 1990s (Simonson 2005) - and certainly more now. Opuntia are the third most important subsistence food source for Mexico's rural poor, so failure of this crop would be devastating (Soberon et al. 2001).
Another associated commercial crop is the natural deep-red dye extracted from the cochineal beetle (Dactylopius coccus) – which feeds on prickly-pear cacti. In Mexico, cochineal dye production constitutes a significant agricultural crop (Simonson 2005). The dye, as a natural product, is considered by some to be preferable for use in foods and cosmetics (http://www.botgard.ucla.edu/html/botanytextbooks/economicbotany/Cochineal/index.html).
The U.S. Department of Agriculture has tried since 2005 to slow the spread of the cactus moth. The USDA Agricultural Research Service (ARS) and APHIS have relied on a program that combines release of sterile moths to disrupt mating and removal of the cactus hosts on the leading edge of the invasion. In cooperation with state departments of agriculture, APHIS has funded surveys in western states to assure that those most vulnerable areas are still free of the cactus moth. A volunteer network managed by Mississippi State University monitors federal, state, and private lands along the Gulf Coast for the presence of cactus moth to ensure any new populations of the species are quickly eradicated.
This integrated program has had some success in slowing the rate of the cactus moth’s spread; nevertheless, it has continued to move westward - to Petit Bois and Horn Islands, Mississippi in 2008; and the swamps and bayous southwest of New Orleans. The Louisiana outbreaks were detected in May 2009 – probably 4 years after the moth arrived there. These swamps are more than 50 miles farther West than the Mississippi islands. (USDA APHIS 2009a).
There would be smaller potential economic losses in the U.S. Depending on what species, if any, expand into areas where the prickly pear cacti were formerly abundant, losses could include reduced revenue from licensed hunting opportunities. In South Texas, higher rents are received for ranchland leased for hunting than for cattle production (Garrett 2004). Ecotourism in the Southwest would probably also be harmed by widespread death of prickly-pear cacti. Just one form of such recreation, off-highway vehicle recreation, resulted in expenditure of $3 billion in Arizona alone in 2002 – with a statewide economic impact of $4.25 billion (Simonson 2005).
While the Louisiana detection was a discouraging setback, researchers taking part in the program review in December 2009 still believed that it is possible to create a barrier to halt further westward spread of the moth by aggressively applying control tactics at the leading edge and managing hot spot infestation to the east of that line. Since there are few cacti in St. Mary Parish or the Atchafalaya swamp, this area might be a good barrier to westward movement; intensive surveys will be needed to verify this approach. Increased funding might enable the program to push the leading edge back to the east, where a better location for the barrier might be the Apalachicola River in Florida (USDA APHIS 2009a).
The moth is spreading much faster along the coast (approximately 75 miles per year) than inland (even in Florida). It will probably move inland faster in TX where cactus density is high throughout the state (USDA APHIS 2009a).
The primary tools for managing the moth at this time are removal of infested host material, limited herbicide treatment to kill cacti, and release of sterile moths (SIT). Monitoring and survey efforts depend on pheromone-baited sticky traps and visual inspections of host plants (USDA APHIS 2009a).
The attractant currently used in the cactus moth lure works, but not for long distances. Another weakness is that it attracts a significant number of non-target moths (USDA APHIS 2009a). Improving the attractant is key to both detecting moth presence and any attempts to use mating disruption to suppress moth numbers (USDA APHIS 2009a). An improved lure is expected to be field-tested by the end of 2010 (Javier Trujillo Arriaga, Servicio Nacional de Sanidad, Mexico, pers. comm. October 2010).
The Program Review team (USDA APHIS 2009a) set out trapping site priorities for Louisiana and called for intensive delimitation survey of the Louisiana and Texas coastline (the latter is 250 miles long) using both traps and visual inspections (USDA APHIS 2009a).
Host plant removal (meaning elimination of all Opuntia from a given area, whether the plants are infested or not) and sanitation (meaning removal of all cactus moth life stages and infested plants) are key components of the containment program. The strategy chosen depends on circumstances (USDA APHIS 2009a). Both strategies depend on finding the cacti. This is difficult since cactus populations are not mapped. The Review Team suggested testing aerial surveys of bayou areas – which could be assisted by the fact that, so far, cacti are usually on spoil banks with trees (USDA APHIS 2009a).
Release of sterile moths has proved effective against small populations. Scientists cannot produce enough sterile insects to flood a large population such as that present in Louisiana. To suppress that large moth population, APHIS planned to focus in 2010 on cactus removal and sanitation; with sterile insect releases scheduled for 2011. Once sterile insect components of the program are instituted, they will face the challenge of delivering sterile insects twice per month to infested areas scattered across large wetlands (USDA APHIS 2009a). The oil spill in the Gulf made access to the area more difficult because of few boats were available for lease. Mexico sent a team of experienced cactus eradicators to assist (Robyn Rose, Entomological Society of America, December 2010).
Cactus moths have been successfully eradicated in limited areas using either complete removal of all cactus hosts (Isla Mujeres, Mexico and Ft. Morgan, AL), or sanitation to reduce the moth population accompanied by sterile insect releases (Isla Contoy, Mexico). Host plant removal was possible where plants could be accessed by vehicles and machinery, and homeowners and officials were comfortable with removing the plants. Sanitation and the SIT were used in protected areas where only limited plant removal was allowed and the plants difficult to access. In order to eradicate Cc in LA, an integrated approach focusing on sanitation, host plant removal and SIT with other control methods utilized on a case by case basis (USDA APHIS 2009a).
Once the cactus moth reaches Texas and the Southwest, biocontrol would be the only probable strategy. Most predators currently known are generalists so they are unsuitable for release. One candidate appears to be a specialist - the braconid larval-pupal parasitoid Apanteles alexanderi; host specificity testing was begun in 2010 in Argentina and Puerto Rico (Strickman 2010). US mainland cactus-feeding moths are poorly known so they will be hard to capture and test for vulnerability to the parasitoid.
Trichogramma pretiosum, a hymenopteran egg parasitoid, has been found parasitizing the cactus moth in the U.S. (Paraiso et al. 2009). While these wasps are available commercially, they offer little promise because they are not host specific and the level of parasitism is normally very low.
The USDA program has been hampered from its beginning by insufficient funding from unstable sources. There has never been an appropriation by Congress for this work. The USDA Agriculture Research Service and Animal and Plant Health Inspection Service have absorbed more than $9 million in costs since 2001. Mexico has provided $1.4 million. Florida Department of Agriculture and Consumer Services, Mississippi State University, and the U.S. Geological Survey (Department of Interior) have also participated in cactus moth control work.
In 2009 APHIS amended its regulations to ensure that Opuntia cactus nursery stock moved from infested states in the southeastern United States would not spread the cactus moth (Federal Register Vol. 74 No. 108 [June 8, 2009], pp. 27071-27076).
The cactus moth has also been introduced to Mexico. In August 2006, it was discovered on Isla Mujeres, offshore from Quintana Roo, in southeastern Mexico. A second outbreak on Isla Contoy was detected in May 2007. These populations have been eradicated with the help of USDA APHIS (APHIS 2009).
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Garrett, L. 2004. USDA APHIS PPQ CPHST. White Paper: Economic Impact from spread of Cactoblastis cactorum in the United States.
Johnson, D. M. and P. D. Stiling. 1998. Distribution and dispersal of Cactoblastis cactorum (Lepidoptera: Pyralidae), an exotic Opuntia-feeding moth in Florida. Florida Entomol. 81: 12-21
Paraiso, O., Kairo, M., Bloem, S., Hight, S.D. 2009. Survey for egg parasitoids attacking Cactoblastis cactorum in North Florida. Meeting Abstract
Simonsen, T.J., R.L. Brown, and F.A. H. Sperling. 2008. Tracing an Invasion: Phylogeography of Cactoblastis cactorum (Lepidoptera: Pyralidae) in the United States Based on Mitochondrial DNA. Ann. Entomol. Soc. Am. 101(5): 899-905 (2008)
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Preliminary assessment of the potential impacts and risks of the invasive cactus moth, Cactoblastis cactorum Berg, in the U.S. and Mexico. Final Report to the International Atomic Energy Agency, April 25, 2005 © IAEA 2005
Soberon J, Golubov J, Sarukhan J (2001) The importance of Opuntia in Mexico and routes of invasion and impact of Cactoblastis cactorumLepidoptera: Pyralidae). Fla Entomol 84:486–492.
Strickman, D. 2010. Research Project: Collection and Evaluaton of Biological Control Agents Against Cactus Moth in Argentina Project Number: 0211-22000-006-11
USDA APHIS C. cactorum Program, Technical Working Group Report, New Orleans, LA, December 1-3, 2009
USDA APHIS. 2009. Eradication of Cactoblastis cactorum, from 11 Parishes in Southeast Louisiana. September 2009 USDA APHIS