The tale of the recent arrival of the cactus moth to Mexico from the Caribbean reaches back nearly a century to the dusty prairies of Australia.

It was there, in 1820, that a well-meaning attempt to create “living cattle fencing” out of introduced prickly pear cactuses turned ugly, as the rapidly-spreading species swiftly took over 16 million acres of land, rendering it nearly useless for agriculture. To control this aggressive invasive plant, Australia began a classic biological control program in 1925: they introduced the prickly pear’s worst enemy – the hungry cactus moth.

The moth won over the hearts and minds of many as it munched its way through acres of the introduced cactuses and constituted a brilliant biocontrol success story in Australia. Soon the governments of India, South Africa, and Hawaii were using it for similar purposes.

But as many invasive species stories go, this one too has a tragic twist.

In 1956, the cactus moth was introduced to the Caribbean island of Nevis. There, again, it successfully controlled the cactus pest. But the moth didn’t stay put. It quickly spread, uninvited, to the surrounding islands, and in 1989 the invader was found in the Florida Keys, where it most likely arrived on a shipment of ill-examined, imported ornamental cactuses.

In the ensuing years, the cactus moth has fluttered across the southern United States, and today can be found in Florida, South Carolina, and Alabama, where it has devastated local cactus populations. John Randall, director of the Conservancy’s Global Invasive Species Initiative, notes that the cactus moth feeds aggressively on a variety of North American species, a worrisome thought for humans and cactuses alike.

On Valentine’s Day, 2007, the Mexican government announced the moth’s arrival on Isla Mujeres, Mexico. This marks a morbid milestone of sorts in its journey across the globe: Mexico is home to 76 species of prickly pear, 38 of which are found nowhere else on earth.

A Battle of Cactus, Moth, and Man

The prickly pear cactus is important to Mexico from more than just an ecological and biodiversity standpoint. The cactus, emblazoned on the national flag and a key ingredient of traditional cuisine and medicine, provides livelihood to more than 50,000 Mexican farm families and accounts for more than $100 million in annual sales nationally. The moth’s arrival in Mexico also raises fears that it could soon make its way to Texas, where it could also have potentially devastating effects on wildlife habitat and rural economies.

To avoid this, The Nature Conservancy has taken steps to control the cactus moth where it has already landed, and is working to prevent it from eating its way through Mexico’s mainland and the southwestern United States. Since 2001, the Conservancy has been a vital part of the development and introduction of the USDA’s “sterile-male release program,” whereby moths are raised on an artificial diet and irradiated to cause reduced fertility or sterility. They are then released in large numbers to mate with females, resulting in fewer or sterile offspring. This program has proved to be effective and the Conservancy expects it to play a major role in the battle against the cactus moth.

The Nature Conservancy has also helped sound the alarm about the cactus moth problem, both within the United States and through the Conservancy’s programs in Mexico. Education is an essential component of any successful strategy against invasive species and, in turn, encourages prevention. Within Mexico, the Conservancy has worked successfully to raise government awareness as well as funds. The Mexican government has even contributed money towards the sterile-male release program in the United States, showing a great awareness that the fight against invasive species reaches well beyond state or country boundaries.

<< Back to Nature New York Spring/Summer 2007

Nature picture credits (top to bottom, left to right): Photo © USDA (Cactus moth); Photo © Ignacio Baez, USDA (Larvae)