INSECTICIDES AND REPELLENTS 75 



compounds substituted. Propyl iV,iV-diethylsuccinamate and di- 

 methyl carbate were particularly effective against the subarctic species 

 of mosquitoes, and mixtures containing them were covered in one 

 specification (No. 21). One of these mixtures is known as M-2020 

 and contains dimethyl phthalate, 2-ethyl-l,3-hexanediol, and di- 

 methyl carbate. The other, M-2043, contains propyl 7V,JV-diethyl- 

 succinamate in place of dimethyl carbate. Until additional infor- 

 mation is obtained on the effects of propyl Af,iV-diethylsuccmamate 

 on women and children, this material alone or in combination with 

 the other repellents named is not recommended for civilian use. 



All these repellents have also shown a high degree of repellency to 

 black flies and a lesser degree to culicoid sand flies. 



In applying a liquid repellent one should shake about 12 drops into 

 one hand, rub the hands together, and smear the repellent in a thin 

 layer over the face, neck, ears, hands, and wrists. It must be uni- 

 formly distributed, as the insects will find places that are inadequately 

 treated. Care should be taken to keep the liquid out of the eyes as 

 it will cause temporary stinging. 



The best repellents should give protection for several hours, but 

 the time will depend on the amount applied, atmospheric humidity, 

 body perspiration, rubbing of the treated areas, and the kind and 

 number of insects and their determination to obtain blood. Perspira- 

 tion particularly affects the protection time by removing the repellent. 

 There is also an unexplained variation in effectiveness between 

 individual users. 



The incorporation of repellents in powder-base creams, particularly 

 zinc oxide preparations, was found to increase the time of protection 

 with the same amount of repellent. Work is under way to develop 

 cosmetic-type lotions that will be more acceptable to the user than 

 liquid repellents. 



REPELLENTS APPLIED TO CLOTHING 



Solid compounds as well as many of the liquids were given screening 

 tests by applying them to articles of clothing and testing them against 

 yellow-fever mosquitoes. When employed in this manner the dur- 

 ation of effectiveness of a repellent is measured in days compared 

 with hours when applied to the skin. The best compounds selected 

 in these tests and nearly all of the class 4 skin repellents were subjected 

 to laboratory and field evaluation to determine the ones most promis- 

 ing for practical use. They were observed for odor, staining, and skin 

 irritation, and from those proved to be safe toxicologically selections 

 were finally made on the basis of duration of effectiveness when the 

 impregnated garments were worn in the field. Nearly all the good 

 skin repellents were effective when applied to cloth, but the best ones 

 on the skin were usually not the most durable on cloth. 



Most of the materials placed in class 3 (effective 6 to 10 days) or 4 

 (effective more than 10 days) as mosquito repellents were also screened 

 as clothing treatments for effectiveness against fleas and ticks. The 

 flea tests were conducted against the cat flea and the Oriental rat 

 flea. For the tick tests, the lone star tick was used in the laboratory, 

 and field tests were run in areas infested with either this tick or the 

 American dog tick. 



