BENZENE AS A LARVICIDE FOR SCREW WORMS 1 
By D. C. Parman 
Assistant Entomologist , Investigations of Insects Affecting the Health of Animals, 
Bureau of Entomology , United States Department of Agriculture 
INTRODUCTION 
The larval stage of CocJiliomyia macellaria Fab., generally known 
among stock raisers in the Southwest as the screw worm, causes con¬ 
siderable loss to the livestock industry, estimated as high as $5,000,000 
in some years. It has been apparent that the larvicides used to 
kill the worms are either toxic to the animal or at least in most 
cases detrimental to the healing of the wounds. This toxicity was 
at first attributed to the screw worm, but as many cases were ob¬ 
served where the animal was practically consumed by the larvae 
and still lived until the loss of blood or injury to some vital organ 
brought de^th, it was surmised that the treatments with larvicides 
were the cause of many deaths. During the summer of 1916 syste¬ 
matic work was begun to find a more efficient larvicide than the 
phenols and chloroform which were generally used. 
At first an attempt was made to add something to these larvicides 
to counteract the toxic properties. As this was not successful it was 
deemed best to look for a chemical that might be used with more satis¬ 
factory results. Several chemical groups were studied for possible 
larvicides. 
EXPERIMENTAL PROCEDURE 
All available chemicals with possible larvicidal value were selected 
for laboratory tests to determine whether they would kill the larvae 
of the screw-worm fly. The first tests were made by pouring the 
chemical on a number of larvae in a tube, or dusting on just enough 
to cover the larvae. All chemicals that stood this test were selected 
for tests on infested rabbit carcasses; and from these, after the elim¬ 
ination of the ones deemed too toxic at the greatest dilutions to be 
used on wounds, the others were selected for field tests on living 
animals. 
CHEMICALS USED IN FIELD TESTS 
Ethyl ether, benzene, toluene, xylene, cymene, carbolic acid, safrol, 
eugenol, ortho-, meta-, and para-cresol, nicotine, pyridine, nitro¬ 
benzene, methyl chloride, chloroform, carbon tetrachloride, methyl 
alcohol, amyl alcohol, formaldehyde, picric acid, formic acid, carbon 
disulphide, sodium cyanide, mercurous chloride, mercuric chloride, 
borax, sodium arsenate, antimony chloride, benzine, gasoline, kero- 
* Received for publication February 21, 1925; issued January, 1925. 
Journal of Agricultural Research, 
Washington D. C. 
( 885 ) 
Vol. XXXI, No. 9 
Nov. 1, 1925 
Key No. K-152 
