366 



SANITARY ENTOMOLOGY 



animals, including man, hogs, dogs, cats and the larger domestic animals, 

 are attacked. 



The flea {Xenopsylla scopulifer Rothschild) occurs on rats in Ger- 

 man East Africa. It is closely allied to A', cheopis and partially replaces 

 that species in the region mentioned. Its possible relations with plague 

 transmission have not been determined. 



FACTORS INFLUENCING ABUNDANCE OF FLEAS 



There is a very close correlation between various climatic factors and 

 flea abundance. This applies to practically all species in greater or 

 less degree. In the United States it may be said that in general fleas 



Fig. 70. — Head of rooster infested with the sticktight flea {Echidnophaga gallinacea). 

 Somewhat reduced. (Bishopp.) From U. S. Dept. Agr., Bull. 248, fig. 7. 



are more abundant during moderately warm weather when there are 

 frequent rains or high humidity. The eff'ect of seasonal and climatic 

 conditions on fleas has a very important bearing on the plague. This 

 has been well shown by the Indian Plague Commission which found that 

 there is a rather close correlation between the abundance of fleas and the 

 prevalence of the disease, and that flea abundance in turn depended upon 

 climatic conditions. They showed that in the case of the European rat 

 flea there is a marked decrease in numbers with the oncoming of the hot, 

 dry season. These fleas begin to disappear in early April and from May 

 15 to November not a single specimen is seen. The Indian rat flea, 

 which is the principal plague conveyer in that region, was found to be 

 above the mean average in number during the period from November to 

 May, with the maximum about April. During the rest of the year — June 

 to September — the flea prevalence is below the mean, the absolute minimum 



