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Periodical cicadas leave Columbia; more bugs on the way

Wednesday, June 29, 2011 | 7:42 p.m. CDT; updated 4:28 p.m. CDT, Tuesday, July 19, 2011
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As the clamorous cicadas fade away, we may be visited by a much smaller pest: itch mites.

COLUMBIA — The periodical cicadas that once overwhelmed Columbia are finally gone.

Yet it doesn’t seem very long ago that resident Donald Bromwell had to hose cicadas off his patio and driveway and stay armed with a flyswatter while he sat outside.

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"I’m 50 years old, and I’ve never seen them this bad,” Bromwell said in early June. "They’re everywhere. It’s annoying; it really is.”

Cicada shells covered lawns, trees and the sides of houses in Columbia throughout late May and most of June. Conversations were often hard to carry on while the cicadas excitedly flew around trees, singing for mates.

Now, as July approaches, the periodical cicadas have disappeared almost entirely. Their mating songs have silenced, and most females have laid their eggs into the branches of trees. 

"There may be a few stragglers around, but they’re pretty much gone," said Rob Lawrence, a forest entomologist with the Missouri Department of Conservation.

The slits created in branches have damaged the trees, and twigs with brown leaves have begun falling.

"Some of the branches that are weakened by cicadas laying their eggs are breaking in the wind and falling," Lawrence said. "We’re seeing quite a few dangling and broken on the trees and some are still attached but turning brown."

With the predicted heat over the next week or so, Lawrence expects to see more browning leaves. There is not much to worry about when this happens, but giving the damaged trees extra water will help, he said.

The periodical cicada eggs will hatch nymphs within six to ten weeks, Lawrence said. After hatching, the nymphs will fall out of the trees and burrow into the ground, where they will remain for the next 13 years until they emerge as adults in 2024.

Lawrence said because Columbia had a heavy population of periodical cicadas, there may be a lot of dead ones on the ground, but he hasn't seen many yet.

“Some people in other places have reported that there is a smell of decaying cicadas if there’s enough of them,” Lawrence said. “I haven’t seen that; I think the birds and dogs have been feeding on cicadas. I’ve found some wings just by themselves lying around, so somebody’s been eating them, apparently. That could be why we’re not seeing so many.”

People may want to get the dead cicadas out of their yard, and though raking them up and disposing of them is one possibility, Lawrence suggests letting nature run its course.

“They’re a good source of nutrition for fertilizing plants.” Lawrence said. “They are beneficial. They’ve been feeding on roots of trees for all these years, and they’re going to provide fertilizer for some of the trees.”

Lawrence recently saw a study that found an increasing growth in trees three to five years after a cicada emergence, indicating that the recycling of nutrients from dead cicadas helped the trees.

This periodical cicada emergence could also result in an increase in the itch mite population.

Itch mites are tiny mites that feed on insects, especially those that form galls, which are abnormal growths of a plant that form when insects feed on it. 

"In Illinois, when they had a different brood of cicadas come out about four years ago, they saw an increase in itch mite activity," Lawrence said.

People were getting bites from itch mites, but there weren't many gall insects in the area or galls on the trees, and it was finally discovered that the itch mites were feeding on the cicada eggs.

"The cicada eggs are inside the cut in the branch, which are similar to the insect prey enclosed in plant tissues that the mites normally feed on, so they were feeding on the eggs," Lawrence said. "Then what happens is at some point the mites drop out of the trees, and if they drop on a person, usually what you see are bites similar to chigger bites."

Itch mite bites are often worse than chigger bites and usually occur on the upper half of the body because the mites are dropping out of the trees.

Lawrence says it is difficult to predict whether there will be a large itch mite population in Columbia because of a severe freeze in April 2007 that killed a lot of foliage and branches in the area. He said the freeze damaged the itch mite population, and he hasn't seen many in Missouri since.

"It's difficult to say whether we're going to have a problem," Lawrence said. "I’m sure they’re still around, but we haven’t had too many reports of them."

Lawrence thinks the itch mite population may rebuild in Missouri because of the increase in food resources this year with the periodical cicada eggs.

The only ways to protect yourself from itch mite bites are to avoid spending time in the woods or under trees, using a DEET-based repellant when outdoors and applying the appropriate medicines to the bites to stop the itching, Lawrence said. He also advises showering shortly after spending a lot of time outdoors under trees or in the woods.

Although the loud, periodical cicadas of Brood 19 are gone, cicadas haven't left Missouri entirely. Annual cicadas will emerge soon.

"The annual cicada, the dog-day cicada, is probably starting to come out here anytime," Lawrence said.

Their population is small compared to the periodical cicada. They are a little bit larger than the periodicals, and they make similar sounds as the periodicals, said MU entomology professor Bruce Barrett.

"Some people won’t even notice these dog-day cicadas that come out because they are so quiet compared to the periodicals,” Barrett said.


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