UF researchers delcare victory in 25-year battle against invasive mole cricket pests

June 15, 2005

GAINESVILLE, Fla. — After a quarter-century fight against three invasive insects from South America, University of Florida researchers are declaring victory against the pests that caused $94 million in damage to turf and pastures each year.

The successful battle against mole crickets is a prime example of how biological control agents can be used to manage pests without conventional pesticides, said Howard Frank, a professor of entomology at UF’s Institute of Food and Agricultural Sciences.

He said the release of three beneficial organisms – wasps, nematodes and flies imported from South America that attack mole crickets – has reduced mole cricket populations in the Gainesville area by 95 percent, and the control is spreading throughout Florida.

Frank, who has coordinated the mole cricket research program since 1985, said four species of mole crickets are found in Florida: northern, short-winged, southern and tawny.

The northern mole cricket, which is indigenous to the state, is not closely related to the three South American invaders, and it is not troublesome because native wasp and nematode species in Florida keep it under control. Unfortunately, the three invasive mole cricket species are not affected by native wasps and nematodes in Florida, he said.

Accidentally introduced to the southeastern United States more than 75 years ago, the pest mole crickets first became a problem for Florida vegetable growers and were poorly controlled with arsenic baits. The invasive pests became a nuisance again in the 1970s when the Environmental Protection Agency banned chlordane and similar pesticides.

“When the three invasive mole crickets left their natural enemies behind, there was nothing to stop their population boom here,” Frank said. “These pest mole crickets, which tunnel into the ground and feed on plant roots, are now found from North Carolina to Texas, and they continue to spread north and west.”

Of the three, the tawny mole cricket is the most destructive, eating grass roots in Florida pastures and turf as well as the roots of tomatoes, cabbages, eggplants and bell pepper seedlings, Frank said.

He said the pest crickets have a real affinity for bahiagrass, Florida’s most common pasture grass, which covers more than 2.5 million of the state’s 35 million acres. Like the pest crickets, bahiagrass was imported from South America, and it provides the insects with an almost endless food source. They also eat Bermudagrass on Florida golf courses.

“Early research on the three invasive pests showed how mole crickets, like moles, burrow into soil around plant roots and prevent them from absorbing water,” Frank said. “We also realized that permanent control of these pests could only be achieved with a classical biological control program, and we began looking for natural enemies in South America.”

In Bolivia, researchers found a native wasp (Larra bicolor) that attacks the pest mole crickets. After the wasp stings the pest mole cricket and lays an egg, the wasp grub (larva) begins feeding on the mole cricket and kills it within two weeks. The wasp attacks all three pest mole cricket species, but does not threaten Florida’s native northern mole cricket.

“By late 1993, it was evident that the Bolivian wasp had become established,” Frank said. “Four years later, the population had spread at least 20 miles east and west of Gainesville. By 2002, it seems to have spread 135 miles northwest and perhaps as far south. In time, it is likely to occupy all of Florida.”

Next stop in the battle against the mole cricket invasion was Uruguay where a parasitic nematode – a tiny, worm-like animal – was found and brought to Florida for mass-rearing and release.

“While other mole cricket natural enemies live above ground, nematodes dwell in the soil where mole crickets do most of their damage – that’s the real advantage of this parasite,” said Grover Smart, a professor of nematology who brought the nematode to Florida in 1985. “The nematode does not affect Florida’s native northern mole crickets, but it does attack all three invasive mole cricket pests.”

Once the parasitic nematode (Steinernema scapterisci) enters the body of a mole cricket to mature and reproduce, it kills the cricket within 48 hours, Smart said.

The third effective biocontrol is a beneficial fly from Brazil (Ormia depleta) that is attracted to two species of the pest mole crickets by the sounds they make.

“Like little guided missiles, the flies home in on singing crickets and lay their larvae on or near the singer,” Frank said. “The larvae burrow into the crickets and feed, killing the host within a week.”

Between 1989 and 1992, researchers released more than 10,000 flies across the state in cooperation with golf courses and the Florida TurfGrass Association. By 1994, the fly had spread to 38 of Florida’s 67 counties, but the tropical insect does not seem to survive permanently north of the Orlando area.