Published: July 15, 2008 11:14 am            

Answers to chigger questions

I have heard some concerns about DEET, the ingredient in most insect repellents. What are the latest findings?

Available under various trade names, those repellents that contain the active ingredient DEET (diethyl toluamide) are the most effective, said Ralph Williams, a Purdue Extension entomologist. Based on extensive toxicity testing the E.P.A. concluded that normal use of DEET does not present a health concern to the general population. To assure safe application follow label directions on products con-taining DEET. Use those products that contain DEET concentrations of 20 percent to 30 percent or less. Apply the repellent to clothing rather than directly to the skin if there is a concern, Williams said.

There seem to be old-wives-tales concerning chiggers. Does Purdue have information on their life cycle and treatment? I have gotten chiggers from weeding in my perennial garden. Can I spray the day lilies area to kill them?

Chiggers are tiny parasitic mites, scarcely visible to the human eye. They attack people, birds, reptiles, and other animals, causing red welts and severe itching, said to Gary Bennett, a Purdue University entomologist.

Contrary to popular belief, chiggers do not burrow into the skin, do not feed on blood, and do not carry diseases. Instead, they stay on the surface of the skin and crawl to the base of a hair follicle to feed.

Once settled, the larva injects the skin with digestive fluids using its piercing, sucking mouthparts, and then they ingest the resulting “cell puree.” The body’s reaction to digestive enzymes that chiggers use to liquefy skin cells causes the rash, intense itching, and misery that begins a few hours after they have fed. Some people are highly sensitive to the chigger’s feeding activity, and their skin will swell and surround the larva. This often kills the chigger. The dead larva within the swollen skin gives rise to the misconception that chiggers burrow into the skin.

Chigger Repellents

Insect repellents such as DEET can help to ward off chiggers. It takes several hours for the chiggers to settle, so bathing immediately after gardening or hiking in weedy areas can significantly reduce the number of bites. Another repellent is Permanone (also sold as Coulston’s Permethrin Tick Repellent). It contains the pyrethroid insecticide permethrin. It should be sprayed on clothing and allowed to dry before the clothing is worn. These products are generally available at sporting goods stores and outdoor-clothing outlets.

Controlling Chiggers Outdoors

Insecticide sprays are most effective when directed into hot spots where chiggers are known to be abundant. Products containing bifenthrin (Ortho Home Defense MAX), carbaryl (Sevin), cyhalothrin (Spectracide Bug Stop Indoor + Outdoor Insecticide), and permethrin (various brands) can be effective. A single application during late-April or May is often all that is required, although in severe infestations, treatment may need to be repeated in June.

The ground and vegetation up to a height of about three feet should be thoroughly wetted with the insecticide and applied according to label instructions. Children and pets should be kept off treated areas until the vegetation is completely dry.

Reducing Discomfort from Bites

n Apply hydrocortisone, Calamine lotion or another over-the-counter anti-itch medication.

n Some physicians may recommend oral Benadryl or a prescription strength steroid cream

— Doug Akers, an Extension Educator at the Boone County Cooperative Extension office, may be reached at (765) 482-0750 or dakers@purdue.edu.

        

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