Field studies of tick repellents were conducted at Bull's Island, S. C., and Camp Bullis, Tex., in the spring of 1948. Thirty-nine repellents, selected from previous experiments, were tested in South Carolina, and 19 of these were tested in Texas. Acetone solutions of each compound, and emulsions and dusts of some, were used to impregnate army cotton fatigue uniforms. The liquids were applied at the rate of about 2 grams per square foot of cloth, and the dusts at 0.1 gram. The uniforms were worn in areas heavily infested with the lone star tick, Amblyomma americanum (L.). Some uniforms were tested daily and others intermittently (weekly for 3 to 5 weeks) after treatment. The ticks in South Carolina were much more active than those in Texas, but the results in the two localities were in general agreement. In South Carolina the ticks were unusually aggressive when the daily tests were under way, and some of the compounds that were highly effective in all other tests gave relatively poor results in this series.
The materials were divided into four groups based on the information available as to their toxicological effects on warm-blooded animals. Of the most effective repellents, those that appeared to be safe for use either on clothing or by direct application to the skin were Indalone, hexyl mandelate, dimethyl carbate, ethyl beta-phenylhydracrylate, 2-butyl-2-ethyl-1,3-propanediol, 2-phenoxyethyl isobutyrate, and diethyl phthalate. Those deemed safe for use on the clothing but not as liquids applied to the skin were N-butylacetanilide, 2-[2-(2-ethylhexyloxy)ethoxy]ethanol, Thanite, hendecenoic acid, isobornyl 4-morpholine-acetate, and 2-phenylcyclohexanol.
The other effective materials were either of undetermined toxicity or appeared to be unsafe for extended use on clothing.
Solutions and emulsions appeared to be about equal in effectiveness. Two compounds gave considerable temporary protection when applied as dusts, even though the dosage was very light.
U. S. Dept. of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine, P. O. Box 3391, Orlando, Florida.