A REVISION OF THE AMERICAN LICE OF THE GENUS 

 PEDICULUS, TOGETHER WITH A CONSIDERATION 

 OF THE SIGNIFICANCE OF THEIR GEOGRAPHICAL 

 AND HOST DISTRIBUTION 



By H. E. EwiNG, 

 Bureau of Entomology, United States Department of Agriculture 



INTRODUCTION 



Because the genus Pediculus includes lice parasitic on man, it has 

 always been one of great interest and economic importance. Head 

 and body lice not only have the disgusting annoyance caused by 

 their parasitic habits, but they are known to be the transmitters of 

 some serious human diseases such as a typhus and trench fever. 

 From a biological standpoint it is in their variation, geographical 

 distribution, and host relationships that the members of the genus 

 offer their greatest interest, and in this respect they have long fur- 

 nished an absorbing although puzzling problem to scientists. Almost 

 a century ago entomologists were saying, but by no means proving, 

 that different races of mankind each harbored a different race of 

 Pediculus. Since then in each decade at least some one writer has 

 renewed the old assertion and in complete conformity with his pred- 

 ecessors has failed to substantiate it. 



When we reflect that it has only been in the last 10 or 15 years 

 that any reliable technique has been employed in the taxonomic 

 study of any of the sucking lice, there is little wonder that the early 

 entomologists with their crude microscopes, or in some cases hand 

 lenses, consistently disagreed with one another in regard to their 

 observations. In the last 10 years methods of clearing, staining, and 

 even dissecting have been developed in connection with the aid of 

 efficient and high-powered microscopes so that now it is possible to 

 ascertain far more accurately small differences which exist among 

 closely related species and varieties. Also time and better transpor- 

 tation facilities have made it possible to enlarge our collections of 

 both hosts and parasites, and thus obtain a better knowledge of their 

 distribution. Because of these new conditions it has appeared to the 

 writer that a revision of the genus Pediculus could be made with 

 profit and some expectation of adding stability to the taxonomy and 

 nomenclature of the group. At first it was hoped that a compre- 



No. 2623— Proceedings U. 3. National Museum, Vol. 68, Art. 19 



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