Consumer Reports (July 1993) ran tests on these agents. Volunteers placed their arms into cages with 500 hungry mosquitoes (Aedes aegypti and Culex pipiens were both tested; Aedes were more aggressive) or 25 stable flies for five minutes hourly for seven hours after repellents were applied. They were then checked for the number of resulting bites.
The products with the highest concentrations of DEET worked best (OFF!, 100 percent; Repel, 55 percent). I and others have had good results on the trail with Ben's (DEET, 100 percent). These products repelled mosquitoes for more than seven hours and flies for more than four hours in these tests. Consumer Reports was cautious about the use of the higher concentration products, especially in young children, and recommended use of lower concentration products. I believe that conditions of use on the trail are more stringent than in the testing situation, with exertion, sweating, rain, and abrasion decreasing the intensity and duration of repellency. Thus I am not optimistic about the efficacy of low-concentration DEET products on the trail.
DEET products are available as aerosol spray, sticks, and liquids. I prefer the liquid because the amount applied and the area to be covered is easier to control. Plastic rims of glasses and similar materials are attacked by this solvent. Do not let DEET irritate the eyes and mouth. On the trail use small and infrequent applications when insect infestation is sparse. Larger and more frequent applications are needed for higher density infestations. Important: DEET is much less effective in repelling ticks.
Several "natural" non-DEET-containing products were essentially ineffective. Thus Natrapel and Green Ban, both containing citronellal, did not repel mosquitoes for even a half hour. Some hikers are convinced that Avon's Skin-So-Soft works as an insect repellent. In these tests it did not repel mosquitoes for even a half hour. Swat, another "natural" product, was similarly ineffective.
Permethrin when impregnated into clothing effectively repels deer ticks, other ticks, and other pests even after three washings. It works well when sprayed on pants cuffs, sleeve ends, and gaiters to prevent tick entry. It helps when sprayed on tent netting against mosquito and fly entry. There are other synthetic pyrethrins that are effective and available. Thus we have some effective means of chemical protection against problem arthropods on the trail.
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