Home Gardening

Cactus cops looking for the cactus moth
Mississippi Gardens Newspaper and Web Column - July 25, 2005

It was the accidental introduction of a serious cactus killer that put government agencies on alert to help save cacti in the United States and Mexico. The call is now going out to the general public to join the "cactus cops", a citizens group dedicated to finding and stopping the spread of an invading pest, the cactus moth, and prevent it from spreading further westward.

It may sound a little bit like the War of the Worlds movie and book story, but we do have a potential insect-related crisis on our hands.

The cactus moth, whose larvae can completely destroy entire stands of prickly pear cactus (Opuntia spp.), is threatening our native population of this unique plant. If it gets past Louisiana it is expected to have a devastating effect on the landscape of the western states and Mexico. USDA estimates the value of prickly pear cactus including nursery production, landscape, and forage at about $70 million per year.

The cactus moth was discovered in the U.S. for the first time in the Florida Keys in 1989. Since then, it has reached as far north as South Carolina and as close to us as Dauphin Island, Alabama. It is anticipated to spread at a rate of approximately 100 miles per year and reach the Texas border by 2007. That puts it on our doorstep about…now.

The cactus moth is brownish-gray and not very noticeable. It lays its eggs in a single egg stick on the succulent pads of the prickly pear. The egg stick resembles a cactus spine and may contain 60 to 100 eggs. The larvae emerge to burrow into the pads and feed together. As they grow, frass and sap are pushed out of the pad and onto the ground. For about five weeks they feed, completely hollowing cactus pads. They may move from one pad to another until they mature and spin white cocoons. Mature cactus moth larvae are bright orange to red with black spots or bands around their torso.

There is a less devastating cactus moth, but its larvae have solid blue or purple coloration.

There are many federal and state agencies partnered together to help stop the spread of the cactus moth, but they need our help. If you have prickly pear cactus in your landscape they would like to know. They are also asking us to report any incidents of cactus decline.

A special Web site has been established for reporting prickly pear location or decline. The address is http://ww.gri.msstate.edu/lwa/invspec/cactus_moth.php. The site has full color photos and contact information.

Your help as a "cactus cop" is greatly needed and appreciated. Happy gardening!

Publications may download photograph at 200 d.p.i.

These archived columns were written by Kerry Johnson, a hobby gardener, former weekly newspaper columnist and an Area Extension Horticulture Agent for 11 coastal counties in Mississippi.