May 02, 2005

LINCOLN, Neb. — Itch mites that plagued eastern Nebraskans last summer and fall are back, a University of Nebraska entomologist said. Although very low numbers are present now, they could be abundant later this fall.

University entomologists collected batches of dropped oak leaves in late February, March and April, said David Keith, university urban integrated pest management specialist. Pyemotes herfsi, an arthropod commonly called an itch mite, prey on the larvae of the gall midge, a small fly, that causes the "leaf edge" galls on pin oak leaves.

"We dissected the old galls, looking for mites, and found a few overwintered female itch mites still alive in a small percentage of these galls," Keith said. "The females were alive and mature and each capable of producing up to 250 young male and female mites. Mites also may be scattered in other places as well, such as in the grooves of tree bark, inside tree holes, beneath buds and other places – we don't really know."

This spring the mites have been relatively quiet, but the university's entomology department did receive two unconfirmed bite reports in mid-April, one from a Lincoln woman who was removing dead leaves by hand from her flower beds, Keith said.

Also this month Entomologist James Kalisch collected thousands of emerging oak gall midges from two sites in Lincoln. The midges were laying eggs on the small pin oak leaves, and small galls already were forming.

"So far, we have not found any itch mites associated with this new crop of galls," Keith said. "However, we are watching the galls as they form and will continue to monitor the establishment and buildup of the itch mites as they attack the midge larvae feeding inside them."

Keith said large numbers of midges seen this spring may be due to the relatively calm, humid and moist conditions. Midges are small and fragile and do not survive to produce high numbers of galls in hot, dry or windy weather.

Since the 2004 outbreak, university entomologists have worked with Kansas State University entomologists to study the mites and answer questions about their life cycle, such as how they overwinter, their full range of host insects, how they transfer to the trees and invade the galls, and how they become so abundant, as they did last fall.

The mites were linked to an outbreak of itchy, red welts received by hundreds of individuals in Lincoln, other southeastern Nebraska towns and cities, and in Kansas, Missouri and Texas.

"While some documentation exists on earlier mite activity, the 2004 outbreak was the first directly attributed to this pest in North America," Keith said.

The bites first showed up last August and continued well beyond early fall frosts into late November and the first week of December, occurring mainly on people who had been outdoors raking leaves, Keith said.

Itch mite bites are red, from one-fourth to three-fourths of an inch in diameter, with a hard, raised "pimple" in the middle. The bites are intensely itchy, but when scratched there is little relief and scratching is quite painful, he said.

Other bites occurred last fall on people who had been mowing their lawns, handling grass clippings or sleeping at night near open windows.

There also were reports of bites where people had been sitting outdoors on surfaces when the mites emerged from the galls. This causes a massive emergence, or "mite shower," when thousands of mites are airborne, Keith said.

This year entomologists will alert local Cooperative Extension offices when "mite showers" may occur. The information also will be broadcast on the gardening information show "Backyard Farmer" on NET1.

"Right now, though, we don't want people to get excited," Keith said. "We do not recommend tree removal, spraying of oak trees to prevent midge galls nor do we recommend spraying lawns for mites," he said. Currently no insecticides are available to control the mites.

"Remember, many other types of critters, such as mosquitoes, chiggers, fleas and black flies, also can bite you and cause red, itching welts," Keith said.

University entomologists make these recommendations:

– For now, go ahead and get outdoors. If there are pin oak trees lining your street, or if your area was affected last fall, keep an eye out for developing leaf edge galls on pin oaks and red and black oaks.

– Wear a DEET repellent when working outdoors under pin oak trees when mites are active.

– During "mite showers", do not handle grass clippings or leaves with bare hands and plan to bathe immediately after mowing near pin oak trees. Do not wear yesterday's clothing without laundering. Plan to take a warm shower and lather well after working in the yard.

– As a general treatment for biting insects and mites, use calamine lotion, an antihistamine cream, such as Benadryl, or a hydrocortisone cream. Wash the site often with soap and use an appropriate antiseptic and antibiotic ointment to keep the wound clean and to promote healing. Don't scratch.

5/2/05-SAK

David Keith - Ph.D.
Entomology
Professor
(402) 472-8918

Sandi Alswager Karstens
IANR News and Photography
(402) 472-3030

Department: Entomology