MEXICO CITY--A non-native moth whose larvae could decimate the country's emblematic prickly pear cactus has been discovered on mainland Mexico for the first time, experts said Wednesday, an event that authorities have feared for decades.

Initial lab reports indicated that at least some of the six moths caught in special traps in the resort city of Cancun in January and February were the same kind of South American "nopal moths" detected last year on Isla Mujeres, just off Cancun's coast.

Hector Sanchez, Mexico's director of plant safety, said the moths probably flew across the narrow strait that separates the island from Mexico's Caribbean coast, or caught a ride on one of the ferries that carry tourists to and from the island.

"The (Mexican) national reference laboratory said that, according to the sample, at least one of the captured moths is of that type," Sanchez said.

But because the moth was smaller in size than the textbook descriptions, that and samples from five other moths caught in the traps have been sent to a U.S. laboratory for confirmation.

Sanchez said workers have erected new traps and are inspecting cacti around Cancun to see if any more than the initial six moths have arrived, but have so far they have not detected any on plants.

Known as Cactoblastis cactorum and native to Argentina, the moth was exported to Australia, South Africa and the Caribbean starting in the 1920s to eradicate cacti that occupied valuable farmland.

But in countries such as Mexico--where flat-leafed Opuntia cacti, known as "nopal," are a food source, an important part of the ecosystem and one of the symbols of the national emblem--the moth poses a major threat.

About 50,000 Mexican farm families make a living off the $100 million annual market for boiled, tender cactus leaves and prickly pear fruit.