CIRCULAR No. 18 



JANUARY, 1928 



UNITED STATES DEPARTMENT OF AGRICULTURE 



WASHINGTON, D. C. 



EXPERIMENTAL DISSEMINATION OF THE 



TABANID EGG PARASITE PHANURUS EMERSONI GIRAULT 



AND BIOLOGICAL NOTES ON THE SPECIES 



By D. C. Pabman ^ 



Assistant Entomologist, Division of Insects Affecting Man and Animals, 

 Bureau of Entomology 



CONTENTS 



Page 



Introduction 1 



Distribution and hosts of the para- 

 site 2 



Physical and climatological conditions 

 of the parasite breeding grounds 

 in south western Texas _ 2 



Life cycle and seasonal activities of 



the parasite 3 



Page 

 Tabanid egg- collecting and parasite 



dissemination 5 



Some factors that have probably con- 

 tributed in controlling the horse- 

 flies 6 



Conclusions 6 



INTRODUCTION 



For a number of years prior to 1913 stockmen whose ranches lie 

 along the south escarpment of the Edwards Plateau, north of Uvalde, 

 Tex., experienced considerable trouble from the attacks of horseflies 

 on their cattle and horses. During the summer of 1913 a rather 

 severe outbreak of anthrax occurred in this region, and circumstan- 

 tial evidence, as well as some investigational work done by the State 

 board of health, indicated that these horseflies played a part in the 

 transmission of the disease. This combination of conditions made a 

 study of the horseflies and their control of distinct economic im- 

 portance. 1 



The study was begun in the summer of 1914, and during the 

 first days of September of that season an egg parasite was found, 

 which was later described as a new species, Phanurus emersoni, by 

 Girault. 2 The horsefly eggs were so abundant at Laguna Crossing 

 on the Nueces River, 20 miles north of Uvalde, that a boy was able 

 to collect 9 pints of egg masses, or approximately 2,000,000 eggs, in 

 one day. In sample masses of these eggs, 97 per cent of the masses 

 were parasitized, and from 6 to 83 parasites emerged from each mass. 

 From these data it was inferred that the most feasible means of 



ir The work was initiated and carried on under the direction of F. C. Bishopp, and the 

 writer is indebted to W. E. Dove for assistance in summarizing the notes and for sugges- 

 tions as to preparation of manuscript and illustrations. 



2 Girault, A. A. a new phanurus from the united states, with notes on allied 

 species. Can. Ent. 48: 149-150, 1916. 

 67824—28 



