IOWA STATE COLLEGE JOURNAL OF SCIE.NCE Published on the first day of October, January, April and July

EDITORIAL BOARD EDITOR-IN-CHIEF, R. E. Buchanan. ASSOCIATE EDITORS: P. E. Brown, Secretary; C. J. Drake, A. H. Fuller, I.E. Melhus, E. A. Benbrook, P. Mabel Nelson, V. E. Nelson. ADVISORY EDITORS: R. E. Buchanan, Chairman; C. J. Drake, E. W. Lind­ strom, I.E. Melhus, P. Mabel Nelson, 0. R. Sweeney.

All manuscripts submitted for publication should be addressed to R. E. Buchanan, Room 110 Central Building, Iowa State College, Ames, Iowa.

All remittances should be addressed to Collegiate Press, Inc., Iowa State College, Ames, Iowa.

Single Copies: One Dollar; Annual Subscription: Three Dollars; In Can­ ada, Three Dollars and a Quarter; Foreign, Three Dollars and a Half.

.. .• . • ; •. . .t> . . . . • • ~ • ·... : i "•. : • - : : • '· ~ ~ ·. ~· ... : : Entered as second-cl~s'. n{atter Januar_Y. 16, i93S,' ~t .ihe postoffice at Ames, Iowa,. under the ~~ ~ Ilf\ircli ~.: ·l~9 ./ ·...... ' . . .. .·:.: ...... : ··... " . .. ' .· ...... ·. ·...... : ..··· .. ··: .··.. : ...... ·· : :•:: ...... ·.. : .. : . ·.·...... ECONOMIC STUDIES OF SCREW WORM , COCHLIOMYIA SPECIES

E. w. LAAKE' From the Division of Affecting Man and Animals, Bureau of Entomology and Plant Quarantine, United States Department of Agriculture Accepted for publication February 19, 1936

INTRODUCTION Heavy losses are suffered each year by the various livestock interests throughout the southwestern part of the United States owing to the de­ structive activities of the screw worm flies, Cochliomyia americana C. & P. and C. macellaria Fab. Babcock and Bennet (1) estimated this damage at $4,000,000 annually. Parman (8) states that the loss in some years has been estimated at $5,000,000, and according to Laake and Cushing (7) southwestern ranchmen estimated the losses in 1928 due to the screw worm and fleece worm at $10,000,000. Screw worm flies are strongly attracted to the slightest wound or dis­ eased tissue of an . Either the living or the necrotic tissues of the host are favorable sites for the deposition of eggs. The feeding of the re­ sulting larvae causes a rapid destruction of the tissues involved and very often death within a few days if treatment is not promptly administered. Parman (8) reports the results of extensive experiments with larvi­ cides for killing the larvae in wounds of animals. Bishopp et al. (2), Par­ man et al. (9) (10), and Laake et al. (6) studied the chemotropic responses of screw worm flies to numerous chemicals with the object of finding a material suitable for wound application and of a strong and lasting re­ pellent power for the protection of the wound from reinfestation. Their studies have yielded valuable information on suitable materials for the destruction of the larvae in the wound and the protection of the wound from reinfestation for a reasonable length of time. Bishopp et al. (3) also point out the necessity of range sanitation to prevent the breeding of myiasis-producing species of flies and suggest modifications in the meth­ ods of range management in order to reduce myiasis during the screw worm season. No quantitative data on the predisposing causes of myiasis or the feasability of controlling myiasis-producing flies by large scale, systematic

1 Part of a thesis presented to the faculty of the Graduate College, Iowa State College, in partial fulfillment of the requirements for the degree of Doctor of Phil­ osophy, March, 1933. • Senior entomologist. The writer is greatly indebted to E. C. Cushing, Senior Entomologist, and H. E. Parish, Assistant Entomologist, Bureau of Entomology and Plant Quarantine, United