Being bugged by swarming aphids? You're not alone

Oct 2 2012 - 6:45am

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Aphids have been swarming in the Top of Utah recently. (Courtesy of InsectImages.com)
Aphids have been swarming in the Top of Utah recently. (Courtesy of InsectImages.com)

OGDEN -- You walk down the sidewalk and are suddenly engulfed in what seems to be a turbulent universe of hundreds of tiny dots, each vibrating as it circles in its wildly irregular orbit.

So, you swat the tiny, gnat-like insects away and rush forward, only to find yourself enveloped in the next busy cloud.

You have interrupted what we will discreetly describe as aphid "speed dating."

"Swarming is usually related to mating," said John Mull, a zoology professor and entomologist at Weber State University. "But the numbers of aphids are clearly exceptional this year."

The tiny winged aphids cling to the clothing of pedestrians passing through their swarms and also coat the windshields of vehicles driving through them.

Aphid populations are swarming in Weber, Davis and Box Elder counties, among others.

"It has to do with a combination of things, including an easy winter and a dry summer, with drought-stressed plants that are vulnerable to pests," Mull said.

Carol D. von Dohlen, associate professor of biology at Utah State University in Logan, said box-elder bugs are big in Cache County, but she hasn't seen an aphid swarm.

"This is a big year for insects. I've never seen box-elders like they are this year," she said.

"With the mild winter and early spring, the insect populations in general are really booming."

Northern Utah is home to a large number of aphid varieties that target various food sources, such as fruit, grass, cereal grains and ornamental plants, including roses.

Aphids insert their stylets -- sucking mouth parts -- to draw juices from plants. Some aphids spread crop diseases, and all sap the vitality of plants.

And the swarming we humans are so rudely interrupting is an end-of-summer effort to produce lots of aphid eggs, which the females will lay in trees.

If we have another mild winter, even more eggs will survive to hatch next spring.

"Aphids have really complicated life cycles," von Dohlen said.

"They reproduce several times during the year, but early on, females will only produce other females until their numbers build up.

"Later, they produce males and females, so they have asexual reproduction in the spring, and this time of year, they have sexual reproduction."

Aphids also produce live offspring in the spring and summer, and in the fall, they produce eggs capable of overwintering, von Dohlen said.

In addition, aphids produce offspring with wings only in the fall, when the tiny insects need to be able to fly up into trees.

"What we are seeing now is the end of their reproductive life cycle for this year," von Dohlen said. "They don't live very long when they get to the point of being winged and mating."

A natural predator for aphids is a braconid wasp, which lays its eggs in immature aphids that have no wings.

Gardeners sometimes turn over a leaf and see the lacy white remains of aphids who played unwilling host to developing parasitic wasps, Mull said.

Agriculturalists have introduced parasitic wasps to crop areas in an effort to control the aphid populations, he said.

And this year's increase in aphids is likely to lead to an increase in parasitic wasps, von Dohlen said.

"That generally does happen. The wasps build up a good population to take care of it, but we no longer live in a natural system anymore," she said.

"Humans plant crops that aphids really love, and they have this huge food source and can multiply their population. Aphids do really well in disturbed habitats.

"I look on campus, where people have planted plants, and I see aphids, but when I go deep in the heart of the natural forest, I don't find that many.

"Aphids aren't strong flyers and don't fly well in undisturbed natural forests. They like to live in plants people cultivate for agriculture or put in their gardens. Aphids like what people like."

But aphids, damaging to crops and rose gardens, are merely pests to the general population.

"They're not poisonous, and they don't bite us," von Dohlen said.

So how much longer must bicyclists pedal with their mouths shut?

"I wouldn't expect the aphids to last too much longer," von Dohlen said.

"The females will lay their eggs, then die. They will be tapering off in the next week or two."

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