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The cactus moth (Cactoblastis) is good at what it does: Destroy prickly pear cactuses.
In fact, it’s so good that the moth has been used from Australia to South Africa as a biocontrol agent to remove the plants from agricultural lands, where the cactuses are seen as nuisances.
But now the cactus moth is doing its job where it isn’t wanted, destroying cactuses from the Caribbean to Alabama. And just last month, the moth was discovered on Isla Mujeres, Mexico — 10 miles offshore from Cancun — perhaps blown there by storm winds.
The moth’s arrival in Isla Mujeres has raised fears that the insect could quickly jump to the cactus-rich Mexican mainland and even devastate the ecosystems of the American Southwest within a few years.
Can the moth be stopped? Nature.org spoke with John M. Randall, director of The Nature Conservancy’s Global Invasive Species Initiative, about detection and control efforts now underway, how the Conservancy has helped lead these efforts, and what more needs to be done.
nature.org: Where has moth infestation so far been the greatest worldwide, and what’s the damage like?
John Randall: Where the moth has been most devastating to cactus populations is probably Australia — but there it was intended to do that.
Where it’s been doing the most damage where it wasn’t intentionally introduced is in the United States—particularly in Florida. It’s attacked a number of native prickly pear cactus species there, including some that are rare. The first place where the moth was identified was actually on a Conservancy preserve in the 1990s, on Torchwood Hammock on one of the Florida Keys. It was hammering a really rare cactus there, and so the alarms went up. And since then it’s spread pretty widely.
nature.org: How far has the moth spread past Florida?
John Randall: It’s not clear how quickly it’s moving through the Gulf States, although it was moving far more rapidly through Florida than was predicted — at 130-plus kilometers [about 100 miles] per year as of 2004. That’s a lot faster than the moth spread in Australia, where it had abundant sources of food. The rapid movement may have been linked to shipment of infected cactus plants for nurseries and maybe also for human food consumption.
The farthest extent west right now is on Dauphin Island, Alabama. It’s not yet been found it any sentinel sites on the border between Alabama and Mississippi. But we have a pincer movement now going on between the threat of the Mexican invasion and this invasion. The fear on the U.S. side is that, if the moth moves further west, particularly into Texas and beyond to Arizona and California, then we’ve got real problems because Texas has quite a few species of prickly pear, as does Arizona.
nature.org: What kind of damage could the moth do in the American Southwest?
John Randall: It could decimate the prickly pear population. It’s known to be doing pretty severe damage to populations in Florida that have not been directly protected—where folks are not caging the cactuses to protect them or picking off the egg sticks regularly. It seems to feed really aggressively on North American species.
nature.org: How would that affect the biodiversity of the region?
John Randall: There would be huge losses. You’d see the loss of a number of animal species, both vertebrates — birds in part — and invertebrates that depend on the cactuses. Key species of birds, most famously in the Sonoran Desert, depend on the cacti for food and nest sites. There are insects whose main source of food is the cactus’s flowers, the plant or the pads themselves. And those insects in turn are food for mammals and birds.
The cactuses also play an important role in holding soil in desert systems as well. We would likely see some problems with soil erosion, which can really be severe in the desert once you lose that fragile cover.
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Nature picture credits (top to bottom, left to right): Photo © iStock Photo (Prickly Pear Cactus); Photo © TNC (John Randall)
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