9 

 MOSQUITO REPELLENTS 



As STATED ELSEWHERE, the Outstanding vulnerability of the larva 

 . has largely prevented practical workers in mosquito control from 

 attempting to use methods against other stages. The same factor has 

 probably been instrumental in minimizing research designed to use 

 other stages for practical control operations. 



There was a long period of time, however, when the only attack 

 made by mankind on the mosquito was devoted to repelling and destroy- 

 ing the adults. History shows that smokes of various kinds have been 

 used to keep mosquitoes away. Various ointments, particularly of an 

 oily, greasy character, have been applied to the human skin to prevent 

 mosquitoes from biting. So we come down to recent times and find 

 ground pyrethrum, otherwise known as insect powder, petroleum oil 

 and various essential oils, recommended for preventing mosquitoes from 

 biting the humans.* 



Mosquito repellents are of two kinds. The first, a mixture of py- 

 rethrins, petroleum oil, emulsifier, and water, is used to spray limited 

 areas to destroy all the adults present and keep the invaders out. The 

 second is some volatile material which, if during the period of its ac- 

 tivity is applied to the human skin, prevents the mosquitoes from 

 alighting and biting. 



The development of repellent mixtures for the treatment of the 



human skin to prevent mosquitoes from alighting and biting has shown 



enough progress to justify a brief account of this work and its results. 



In the year 1935 Mr. George C. Furness, representing the National 



Carbon Company, approached the author on the subject of a grant- 



* A brief but comprehensive sketch of this matter occurs on pages 365-367, Volume 

 1 of The Mosquitoes of North and Central America and the West Indies, by Howard, 

 Dyar, and Knab. Even as late as 1939, Dr. F. C. Bishopp, writing in Leaflet No. 

 186 of the Bureau of Entomology and Plant Quarantine, U. S. Department of Agri- 

 culture, summarizes the repellent situation as follows: "There is no known substance 

 that will give complete freedom from mosquito attack for more than a few hours. 

 Oil of citronella is probably the most dependable. If oil of citronella is objection- 

 able because of its odor, it can be mixed with spirits of camphor or oil of penny- 

 royal in equal proportions. Certain cut or growing plants have been reported to 

 drive mosquitoes away, but none of these is of practical value." 



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