State aids resident's mosquito problem After pesticides fail, agencies put tadpoles, mosquitofish in pond

September 25, 1995|By Andrea F. Siegel | Andrea F. Siegel,SUN STAFF

When citronella candles, an electric bug zapper and Malathion didn't kill the swarm of mosquitoes behind her home, deLois Steverson-Nicholas called on Mother Nature and the simple logic of the food chain.

On a muggy June afternoon, the Maryland Department of Natural Resources dumped 1,500 tadpoles and frogs into the nameless pond behind her Highland Beach home. It was a first for the department, and it worked.

Tadpoles are vegetarians. By metamorphosis, they become bullfrogs, omnivores whose diet includes insects.

"It's biological control," said Jay Feldman, executive director of the National Coalition Against the Misuse of Pesticides. "It is reintroducing cultural practices that pest managers have gotten away from on the promise that chemicals would be better."

But don't give the bullfrogs all the credit. Later that same week, the state Department of Agriculture brought two coolers of mosquitofish, which take their name from their eating habits. They gobble mosquito larvae, and the agency relies on them for insect control.

"The mosquitoes, they have been lighter," Ms. Steverson-Nicholas said last week. "We did have a party out there in July. And it turned out fine."

That's quite a difference from the June evening party that was broken up by an invasion of mosquitoes.

DNR's just-for-fun experiment was neither planned nor scientific nor coordinated with its sibling agency. Had it been, Bob Lunsford, chief of DNR's fresh water fisheries division, probably would not have brought young bullfrogs.

However, when Ms. Steverson-Nicholas called asking for anything that would devour her mosquitoes, the young frogs were all that was left in the division's hatchery ponds in Charles County. He figured it was worth a shot.

Usually the amphibians get dumped into a swamp. Mr. Lunsford said he will consider making tadpoles and young frogs available next year, if there is interest.

The Agriculture Department prefers mosquitofish, or gambusia, for its statewide mosquito-control program, said Kevin Sweeney, who runs the program in the county. The fish are considered efficient because they eat mosquitoes in the larval stage. Frogs, on the other hand, go for energy-efficiency. They want the biggest meal possible, biologists say.

Both state agencies are taking some credit for the success behind Ms. Steverson-Nicholas' house, which is fine with Mr. Feldman.

"The agencies are to be congratulated on their initiative," he said.

Mosquitofish can live in water that has less dissolved oxygen than tadpoles need for survival, said Mr. Sweeney. Many tadpoles were dead when his crew came to the pond, he said. But, countered Mr. Lunsford, bullfrogs are more likely to survive a cold winter.

And, the food chain is such that a full-grown bullfrog, weighing up to a pound, could eat a mosquitofish. That makes it important to keep the pond stocked with young and small frogs. Big bullfrogs prefer bigger prey than mosquitoes, such as mice and small snakes.

The Nicholas family shares ownership of the fresh-water pond with a neighbor who agreed to let Ms. Steverson-Nicholas pursue natural insect control. With the success of Mother Nature comes an equally natural drawback: the springtime croaking of male bullfrogs attracting mates. Ms. Steverson-Nicholas said she expects to adjust to the frogs next year.

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