Impacts of mosquito spraying to be investigated after dead tadpoles found

FARGO -- Some 300 tadpoles that 11-year-old Ahren Wagner was raising in a kiddie pool behind his house died last week the day after a truck spraying for mosquitoes passed by.

"They were all dead," he said. "Except one, and it died later."

A biology enthusiast who recently graduated from Longfellow Elementary School, Wagner said he worries the spraying is damaging the local ecosystem and possibly killing useful natural predators of mosquitoes, such as frogs. "It doesn't only kill mosquitoes."

Mosquito fighters at Cass County Vector Control, who received an email from Wagner last week, are aware that spraying pesticides can have an impact on the environment, according to Director Ben Prather. There is no question that it kills helpful insects such as dragonflies, which also eat mosquitoes, he said. But that also must be balanced with the demand for eradication of pests that annoy people and can carry diseases, he said.

Though permethrin, the pesticide that Vector Control uses, is safe enough to be found in household products, Prather said spraying is the last resort when more targeted killing of mosquito larvae are no longer effective.

The nearly 8 inches of rain that fell over the metro area last month has led to a population boom that his crews are still struggling to control, he said.

The bigger question

Wagner's and Prather's competing views are representative of the debate between environmentalists and conservationists on one side and pest control and public health officials on the other.

Some environmentalists believe that natural predators should be used to control the adult mosquito population. These include not just frogs and dragonflies but purple martins and bats. To date, there appears to have been no experiments that prove or disprove biological control can be effective.

But scientists who study biological control or "biocontrol" say that for a predator to be successfully used in mosquito control it would need to breed as fast as mosquitoes to respond to the population boom. For this reason, studies on biocontrol methods have primarily focused on parasites, fungus, bacteria and viruses.

Mosquito-control professionals maintain that they must rely on chemical pesticides for now. Many agencies, like Cass County's, focus most of their efforts on killing mosquitoes while they're still waterbound larvae. The pesticide used for that is Bacillus thuringiensis israelensis, a bacteria naturally found in the soil.

Spraying begins when the mosquito traps around the metro area average 35 female mosquitoes, the only kind that bites, but Prather said he gets calls from many itchy and annoyed residents even before that.

Backyard biocontrol

In their backyard overlooking the Red River, the Wagner family has been using frogs as biocontrols for the past couple of years and they said it seems to have worked.

"I started being interested in frogs quite a while ago," said Wagner, whose room has two aquariums and a terrarium. A few years ago, he began collecting frogspawn with some friends at a nearby bog and raising them in the backyard.

Of about 300 tadpoles, usually 10 make it to full-grown frogs, he said. He places some in the family garden to take care of pests, he said.

"It was his idea to put the frogs in," said his mother, Heather Ummel-Wagner. "My goodness, it really kept down on pest control."

On Monday evening, the night of the spraying, he suggested to his parents that a tarp should be placed over the kiddie pool to protect them, but his parents didn't think they would be harmed.

"Nature boy was right," Ummel-Wagner said. "Should have listened to your instinct."

She said she called a Vector Control official who seemed surprised that the spray "had affected more than just mosquito life."

Prather said the agency has related the incident to the North Dakota Department of Agriculture. If the Wagners were to file a complaint, he said the department would probably open an investigation.

So far, the department said it has not received any such complaint.

Evidence and observations

Wagner is not totally satisfied with the agency's response.

"It's nice that they're not just like, 'Whatever,' but it would be good if they did something to fix it."

He would like to see an end to the spraying in favor of the promotion of natural predators of mosquitoes. On a trip to a lake, he saw an example of a healthy ecosystem in action.

"No one sprayed around there and there were a ton of dragonflies and tons of frogs and fish and everything," he said. "There were barely any mosquitos there. It was just like, one mosquito in the air, that gets eaten by a dragonfly."

Prather said he would be happy to let nature take care of the mosquitoes but his experience suggests it wouldn't work that way. Vector Control sprays only about 10 percent of Cass County, mostly the urban area, he said. Often after a spray has taken care of the mosquitoes in town, he said, the living ones from unsprayed areas will move in to take their place.