Invasive Moth From Tropics Threatens Cactus Plants In U.S.

April 26, 2005

GAINESVILLE, Fla. — In a prime example of how Florida is becoming a haven for exotic pests, a South American moth is attacking valuable ornamental cactus plants used in landscaping and could be a threat to the nation’s $70 million cactus industry.

First spotted in the Florida Keys about 15 years ago, the tiny moth has already spread northward to Alabama and South Carolina. Now, University of Florida entomologists say the invasive pest could spread even farther, attacking natural and cultivated prickly pear cacti in other areas of the United States.

Jim Cuda, an associate professor of entomology with UF’s Institute of Food and Agricultural Sciences, says residents should be on the lookout for the cactus moth (Cactoblastis cactorum) and the damage it causes in yards, plant stores and nurseries. Suspected infestations of the pest should be reported to the U.S. Department of Agriculture in Tallahassee.

Cuda, who believes the spread of the insect may have been hastened by hurricanes in 2004, said the pest is troublesome because there are no natural enemies to stop it. The insect feeds only on prickly pear cacti.

“Surveys for natural predators that could be imported for effective biological control of the moth are being conducted by USDA scientists in South America, and they also are testing a sterile insect release program, but their effectiveness has not yet been determined,” Cuda said. “Widespread use of pesticides is not practical because the pest potentially inhabits thousands of square miles in Florida alone, including habitat for the endangered Schaus’ swallowtail butterfly.”

The pest could threaten rare U.S. prickly pear cacti that are not cultivated, said Richard Moyroud, chairman of the Florida Endangered Plant Advisory Council and owner of Mesozoic Landscapes, a native plant nursery in Lantana, Fla.

“Once something as tiny as this moth gains a foothold in area where it has no enemies, stopping it is almost impossible,” Moyroud said.

The moth is one of several recent insect invaders to threaten ornamental and food crops in Florida, along with the pink hibiscus mealybug, Asian citrus psyllid and Diaprepes citrus root weevil, Cuda said.

The moth can fly short distances, but it is believed to spread primarily via transportation of infested plants, he said. The moth leaves two distinct calling cards. Female moths deposit stacks of tiny eggs on the sides of the fleshy cactus pads, and the stacks resemble inch-long cactus spines. These stacks of eggs are called eggsticks. When caterpillars hatch from the eggs, they burrow into cactus pads to feed, leaving tiny holes that ooze a green, slimy fluid.

The eggsticks can be removed from cactus pads and frozen before being discarded, he said. Any pads infested with caterpillars should be removed from the parent plant, wrapped securely in several layers of plastic, held in a freezer for three days and properly discarded.

The caterpillars, which are tan or orange with distinctive black traverse bands, can be found by cutting open infested cactus pads. Adult moths are gray and white with a wingspan of about one inch. Casual observers are more likely to notice holes in the cactus pads than see moths, Cuda said.

Stephen Hight, a USDA research entomologist in Tallahassee, said residents should report sightings of the pest by calling him at (850) 656-9870 or e-mailing him at
Hight@nettally.com.

“If the sighting is from an area where we know the cactus moth is found, we can offer suggestions for controlling the pest,” Hight said. “If the sighting is from an area that’s new, we need to make sure the culprit really is the cactus moth, and we may ask people to contact their local county extension service agent for confirmation. Or, we may ask for a digital photo.”

Cuda said there are some 31 species of prickly pear cactus in the United States, including six that are native to Florida. Also known as opuntia, prickly pears are used in drought-resistant landscapes across the country. Some species are also used in foods, particularly in salads and Mexican dishes. The U.S. cactus industry has a total estimated value of $70 million per year.

In Mexico, home to more than 50 species of prickly pear, the cacti are important food sources for people and cattle. Mexico’s cactus industry generates $50 million to $100 million per year, so the cactus moth would have a devastating impact if it finds its way into the country, Cuda said.

“We don’t want this pest to spread any further – if we can determine exactly where it is now, we can concentrate our control efforts,” Cuda said.

For more information about the cactus moth, visit
http://creatures.ifas.ufl.edu/bfly/cactus_moth.htm.