Malathion and mosquitoes

Insecticide may have harmful consequences

As the local mosquito plague continues, more homeowners are taking the fight into their own hands - and the consequences could be unhealthy.

Flathead County's mosquito control efforts focus on mapping problem areas and treating them with larvicide. The county does not spray to kill adult mosquitoes.

But with massive insect hatches in June, limited county funds and staff, millions of mosquitoes are buzzing around and on the lookout for exposed skin.

To attack the attackers, homeowners are spraying large quantities of malathion, a common insecticide.

Malathion is an organophosphate that assaults the nervous system. If used correctly, the poison poses a small risk to humans and pets.

But that's a big "if."

At a recent Mosquito Board meeting, two beekeepers spoke of their concerns that indiscriminate and incorrect use of malathion would wipe out a large number of pollinating bees.

With the sales of malathion and mosquito foggers on the rise, their concerns may become reality. Spraying poison during the day, especially if there are flowers nearby, most likely will kill honeybees.

As bee populations continue to struggle - and in some cases plummet - beekeepers hope to mitigate the problem posed by poison.

Linda Andersen, a department manager for Cenex Harvest States, said there has been a definite rise in local sales of malathion. Andersen pointed out that people are buying less toxic products such as permethrin as well.

"We're starting to sell more and more natural products," she said. "They are a little less toxic and a little less smelly."

Flathead County commissioners have prohibited the mosquito control district from using malathion, and mosquito control coordinator Bruce Gunderson has expressed concern about the public use of malathion.

"I've heard horror stories of what people are putting out there," Gunderson said.

People treating their property have done everything from using malathion at concentrations two and three times the necessary amount to pouring diesel fuel into standing water.

Gunderson said that the mosquito population is dwindling somewhat, and people may be incorrectly attributing their use of malathion as the reason.

"What some people are interpreting as their success maybe isn't exactly true," he said.

Patricia Denke, the pest management section supervisor for the Montana Department of Agriculture, said widespread use of malathion by homeowners is not a good idea.

"Organophosphate insecticides, those are nerve poisons," Denke said. "These things do have risks. They are designed to kill."

Denke, who has a Ph.D. in Entomology in mosquito ecology, said using insecticide at higher concentrations than recommended is illegal.

"The label is the law," she said. "That goes for whatever you are doing with an insecticide."

Not only are people using malathion at elevated concentrations, but they also may be applying it incorrectly.

The best time to treat mosquitoes is generally from dusk until 2 a.m. Malathion, Denke said, should be aimed into the air, not at plants, shrubs and grass.

"Do you want your kids playing in a yard that is constantly bathed in insecticide?" Denke asked.

Denke recommends an integrated approach to combat the mosquito problem.

The first thing she recommends is working with the county's mosquito control staff. If the county doesn't know where all the problem areas are, it can't get an early jump on treatment for the next season.

Second, get rid of and treat standing water. Killing mosquito larvae is much more effective that trying to kill the adults.

"If you can treat an acre of mosquito larvae, you have treated potentially 72,000 acres of adults," Denke said. "They spread out. Some of them will go 20 miles. That's another reason to skip spraying your yard."

Treating one backyard is nearly useless when a mob of more adult mosquitoes can simply fly over from the neighbor's yard.

Third, coordinate a widespread effort.

Foggers scattered through random yards isn't an effective measure, and may make matters worse. Mosquitoes that are resistant to malathion will survive and continue to breed, which will create a larger population of poison-proof blood suckers.

Reporter Michael Richeson may be reached at 758-4459 or by e-mail at mricheson@dailyinterlake.com