Mosquitoes are flourishing this summer, a local environmentalist says, but if you spray common insecticides to get rid of them you'll likely get rid of the good bugs, too, insects that benefit us. Credit: Gilles San Martin / Creative Commons Gilles San MartinGilles San Martin

I’ve read the statistics. I know bumblebee populations have declined by 90% and up to a third of firefly species may risk extinction.

That’s why I grow milkweed and pollinator plants and leave leaf litter for firefly larva. But am I making a difference? Do I see more monarchs? Mason bees? Moths?

The only insect I can vouch for is the mosquito. Populations appear to be flourishing, judging by yard signs, flyers and billboards promoting mosquito spray services.

From my side of the fence, the problem is this: If someone sprays a fine mist of pesticides at the shady, flower-free areas where mosquitoes rest, it won’t just kill mosquitoes.

“It can impact bees, butterflies, moths, caterpillars and insects that birds depend on as a food,” says David Mizejewski, a naturalist with the National Wildlife Federation.

The risks for pollinators can be obscured by the fact that backyard sprays commonly contain synthetic pyrethroids and insecticides that are related to natural pyrethrins found in chrysanthemum flowers. While chemically similar, synthetic pyrethroids are not eco-friendly or plant-based. They are broad-spectrum nerve toxins that the EPA says are “acutely toxic to bees and other insects.”

In a home setting, sprays with synthetic pyrethroids don’t just kill during the application process, which is brief. They dry on foliage and persist, turning the simple act of landing on a leaf into a potentially fatal event.

“Permethrins and other pyrethroids can be toxic to insects that eat or touch them during the residual activity period, which is usually two to four weeks after application,” says Dr. Paula M. Shrewsbury, associate professor of entomology at the University of Maryland.

What insects are we talking about?

Unlike honeybees, a European import, native bees, which include bumblebees, leaf cutter and mason bees, make their nests in the ground or lay eggs in stems, old logs and above-ground cavities.

With the exception of bumblebees, most native bees don’t live in hives. Males are banished from the nest once they are reared. Heather Holm, author of four bee and pollinator books, explains that, “until they die, male solitary bees are out in the landscape, clinging to foliage, sitting in flowers. They would be directly impacted by foliage spraying.”

“Go out on a chilly morning,” says Colin Purrington, a nature photographer and avid entomologist in Swarthmore, PA, “and you might find a couple of dozen male bees clamped onto a single plant with their mandibles. Multiple species could be there, just hanging out.

Later in the day, you might see fireflies and moths, resting in shade, dodging predators and conserving energy for nocturnal flights. On the underside of leaves—a prime mosquito spray spot — you could find butterfly eggs. Butterfly and moth caterpillars might be munching their way to maturity — or getting snapped up by a hungry bird.

Area-wide disease control and mosquito population suppression is the job of county mosquito control agencies. “We would encourage folks to not spray in their own yards and let the county take care of it,” says David Brown, Technical Advisor to the American Mosquito Control Association. One reason, he says, is growing mosquito resistance to pyrethroids. “If you can manage the habitat in a manner where it reduces the likelihood that mosquitoes will emerge, it’s a win-win.”

Start by eliminating standing water. Female mosquitoes will lay eggs in the half-inch of water lingering in a flowerpot saucer. Common breeding grounds include old tires, corrugated pipes, leaf-clogged gutters, puddle-filled tarps and children’s forgotten toys.

Vigilance won’t stop mosquitoes from flying in from your neighbors’ yards. Successful ways to ward them off include oscillating fans (mosquitoes are weak flyers) and traps that lure female mosquitos and prevent their eggs from hatching. Purrington uses a selection in his yard and discusses them on his website. Douglas Tallamy, author of the best-seller, “Nature’s Best Hope,” has popularized a DIY trap made with a five-gallon bucket, water, straw and a Mosquito Dunk, a larvicide.

Targeted strategies are cheap, effective — and far better for the pollinators.

Claire Whitcomb is a sustainability writer and chair of the Madison Environmental Commission.

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