UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1472 
Washington, D. C. 
March, 1927. 
CHEMOTROPIC TESTS WITH THE SCREW-WORM FLY 
By D. C. Parman, Assistant Entomologist, F. C. Btshopp, Entomologist in 
Charge, and E. W. Laakb, Associate Entomologist, Investigations of Insects 
Affecting the Health of Animals. Bureau of Entomology, and F. C. Cook, 1 
Physiological Chemist, and R. C. Roark, Associate Chemist, Insecticide and 
Fungicide Laboratory, Miscellaneous Division, Bureau of Chemistry 
CONTENTS 
Introduction _ 1 
Work of other investigators with fly repellents. 2 
Materials now used as screw-worm fly repel- 
lents 3 
Purpose of chemotropic tests 3 
Materials tried 4 
Procedure 5 
Method of computing results 6 
Tabular statement of results of tests 7 
Page 
Discussion of results 22 
Compounds 22 
Organic products 26 
Best repellents 27 
Materials exhibiting a perfect repellent ac- 
tion for periods of from two to five days.. 30 
Relation between repellent action of com- 
pounds and their composition and volatility. 30 
Summary 31 
INTRODUCTION 
Throughout the southwestern part of the United States heavy 
losses are suffered each year by the various livestock interests owing 
to the destructive activities of blowflies. Although the farmers 
and dairymen have considerable trouble with these insects, the losses 
are most severely felt by the cattle, sheep, and goat raisers on the 
ranges. 
The species commonly known as the screw-worm fly, Cochliomyia 
macellaria Fab., is by far the most destructive of the blowflies. 
The average annual loss due to this insect has been estimated at 
$4,000,000. It breeds normally in dead or living animal tissue. 
When the flies are abundant they are strongly attracted to the 
slightest scratch or blood spot on the skin of an animal. Under 
_v favorable conditions oviposition takes place, and the larvae hatch 
and start feeding on the living tissues of their host. The larger 
the wound the more attractive it becomes, and the infestation con- 
tinues to increase, resulting in extensive destruction of tissue and 
very often the death of the animal if treatment is not administered 
within two or three days. 
J Died June 19, 1923. Since May, 1924, R. C. Roark has been the representative of the Bureau of 
Chemistry in this investigation. 
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