GRI Collaborates to Create Database to Monitor Spread of Cactus Moth

Geosystems Research Institute
March 4, 2005

The survival of indigenous prickly pear cacti along the coastal areas of the southwestern United States is threatened by a spotted black-and-orange caterpillar. Once hailed as a hero in Australia for controlling unwanted populations of exotic prickly pear cactus, the caterpillar-a larvae of the cactus moth-has quickly established itself as an American pest threatening native landscapes and agricultural industries in the southwestern United States and Mexico.

The United States Department of Agriculture estimates cactus has a trade, nursery, landscape, crop, and forage value of up to $70 million a year, mainly in the Southwest. In Mexico, cactus is estimated to be a $50 million to $100 million a year industry.

Discovered for the first time in the Florida Keys in 1989, the moth has since eaten its way up the eastern seaboard to Bull Island, S.C., and along the Gulf Coast to a barrier island in Alabama. Moving at a rate of approximately 100 miles annually since 2000, the moth is expected to reach the Texas border by 2007.

"We believe the cactus moth populations are concentrated in coastal areas of the southeastern United States due to the availability of abundant hosts on the barrier islands," said Joel Floyd, a planning and preparedness specialist with USDA APHIS. "Host plants are available to a much lesser degree in habitats inland from infested areas."

The cactus moth has been found to eat most prickly pear cactus with flat pads in the genus Opuntia. Approximately 72 species of prickly pear are recognized worldwide, 53 of which occur in Mexico. The members of the genus Opuntia known as "Cholla" cactus are not normally hosts of the cactus moth.

In a race against time, the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (USDA APHIS) has joined forces with the USDA Agricultural Research Service (ARS) to prevent the westward spread of the cactus moth. Beginning in spring 2005, researchers will launch a large-scale sterile insect technique validation study on barrier islands in Florida and Alabama to determine whether the moth's western movement can be halted.

Believed to be the most promising control method to date, the sterile insect technique involves the release of mass-reared sterile moths to limit the reproductive capability of healthy females. The major benefit of this technique is that, unlike chemical controls, there are no adverse impacts to related moth species or the surrounding environment.

In addition to partnering with USDA ARS to conduct the validation study, USDA APHIS has partnered with the state departments of agriculture in the southern United States to survey nurseries and homeowner properties for cacti infested by the cactus moth. As a complement to the homeowner surveys, the U.S. Geological Survey (USGS) of the Department of the Interior has developed a survey program to monitor the spread of the cactus moth on public and private lands, including national parks and wildlife refuges. USGS is working with Mississippi State University's Georesources Institute on a database to track the monitoring data. A major advantage of establishing a survey program on conservation lands include ready access by researchers and constant monitoring by resident managers and stewards.

The cactus moth (Cactoblastis cactorum) is a relatively non-descript brownish-grey moth, which deposits its eggs on to egg sticks that resemble cactus spines on cactus pads. The feeding larvae then cause physical damage to the plant by hollowing out and destroying cactus pads that have not yet become woody. The larval damage also enables bacteria and other microbial organisms to enter the plant and cause secondary infections, which contribute to the death of the plant.

So serious a threat is the cactus moth that USDA APHIS is not only working to control populations already established in the United States, but also prohibits the movement of cactus plants and cactus parts from Puerto Rico and the Virgin Islands to the mainland to prevent further introductions of the pest into the country. USDA requires that all plants, including cacti, imported into the country for propagation be accompanied by a health certificate and inspected at a USDA APHIS plant inspection station where plant material found to be infested by the cactus moth is fumigated, destroyed, or returned to its country of origin.

For more information on the cactus moth and the government's efforts to track and record cactus moth populations, please visit the following websites: -- Original article appeared in the March 2005 Invasive Species of the Month issue of the National Invasive Species Council's website.

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