K-State Entomologists Shed Light On Little Mites Causing Big Problems 9/22/04

MANHATTAN, Kan. – Scientists have found that what’s been bugging people in southeast Kansas is the straw itch mite, but the news has prompted even more questions about the tiny pest, two Kansas State University entomologists said.

“What’s typical for these mites is that there is no pain … no sensation when someone is first bitten,” said K-State Research and Extension entomologist Alberto Broce, one of several scientists who traveled to Crawford County to determine the cause of the outbreak. “People typically don’t know they’ve been bitten until the next day when they wake up with the red, itchy welts.”

In most cases, the bites are no worse than that -- itchy welts that last for a few days, he said. There have been a few reports, however, of people having a more severe reaction, including fever.

What is a Straw Itch Mite?

MANHATTAN, Kan. – An unusually large outbreak of straw itch mites has been reported in southeastern Kansas this year. Two Kansas State University entomologists, Alberto Broce and Ludek Zurek, provided details about the microscopic pests. The straw itch mite:

Scientific name is Pyemotes tritici.

Measures 1/125 inch long.

Feeds on a broad variety of insects. Common to all their hosts is that they are found in protected habitats such as galls and stems, a trait aimed at protecting the immobile, gravid female.

Newly emerged and mated females inject venom-containing saliva into their hosts that paralyzes them and thus prevents harm being done to the female.

The female abdomen enlarges as its progeny develop. Within a few days, up to 200 adult mites emerge from the gravid females.

Newly emerged males position themselves near the mothers and mate with emerging females. This is the stage at which these mites disperse to colonize new habitats invaded by insect larvae. But if they land upon vertebrate hosts such as humans, they will attempt to feed on them with the resulting itchy bites.

The outbreak first made news three weeks ago when a football team from Colorado went home covered with bites after a game at Pittsburg State University in Pittsburg, Kan. Soon after, the Crawford County Health Department fielded calls from area residents complaining of similar bites, said K-State entomologist Ludek Zurek.

The mites are so small they cannot be seen by the naked eye, Broce said. Some bites might be just tiny bumps, but frequently they are quarter-size reddened welts with a pimple in the middle, and most commonly found over the neck and shoulders and areas of the torso where clothing fits loosely.

The K-State entomologists worked with scientists from the Crawford County Health Department, Pittsburg State University, epidemiologists from the Centers for Disease Control and Prevention in Atlanta and the Kansas Department of Health and Environment to identify the pests.

Outbreaks have also been reported in Joplin, Mo. and Lincoln, Neb. and are suspected in Tennessee.

Working with entomologists at the University of Nebraska, the scientists found many of the mites inside leaf galls on oak trees, Zurek said. Leaf galls - those small raised lumps on tree leaves - are caused by parasitic insects. Apparently, the tiny straw itch mite feeds on larvae of these insects inside of the galls, primarily on oak trees, he said.

“People are not their primary hosts,” Broce said. “However, they will bite people when their preferred hosts are not around. Plus, the mites are so small that they can be carried for some distance on the wind.”

“Although outbreaks in Kansas such as this year’s are very unusual, the mites likely have always been here – just not in such large numbers that we seem to have this year,” Zurek said.

Zurek and Broce believe the mite population grew larger than usual because of this year’s relatively cool, wet weather, which might contribute to an increase in gall-making insects. Those insects thrive in such conditions and what’s good for the them is obviously good for the straw itch mite population that feeds on them, they said.

The first good freeze should put an end to the outbreak – at least for this year, Broce added. There’s no way of telling, however, if the pests will be around in such large numbers next year.

People in areas identified to have straw itch mites can take steps to keep from being bitten, the scientists said. Those who have been under or near oak trees should change clothes and shower after coming indoors. Using a repellent with DEET should also provide protection.

In cases where someone has already been bitten, calamine lotion will help sooth the itching caused by the bites.

Spraying the oak trees is not likely to be effective, they said, because the mites are protected inside the leaf gall.

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.