PROC. ENT. SOC. WASH., VOL. 20 No. 5, MAY. 1918 97 



As an example of the necessity of understanding tin- life history 

 of the tick I may cite the case of Haemogregarina H////.S, cause of 

 canine anemia, which is carried by the dog tick Rhipicephalus 

 sanguineus having the third type of life cycle. For sometime 

 investigators were unable to understand how the parasite reached 

 another host, as parasites taken up by the adult did not complete 

 their cycle of sporogony in the tick. Finally Christophers dis- 

 covered that only those parasites taken up by the nymph com- 

 pleted their development in the adult tick. Between the nymphal 

 and adult stages this tick drops to the ground and attacks a new 

 host. We have then an easy explanation of the transmission from 

 one host to another. 



It is just as important to know the life history and breeding 

 places of mosquitoes. Dr. Carter has very recently called 

 attention to the necessity of accurately determining the extent to 

 which Anopheles punctipennis carries malaria, as the measures 

 necessary for the control of this species would add millions of dol- 

 lars to the cost of malaria control in this country. 



During the past two years it has been my privilege to spend 

 most of my time searching the literature of the world for references 

 to the relations of insects to disease. In making this study I 

 have noted a number of outstanding features. 



Bacteria and Insects 



A brief tabulation made at the beginning of the work had led 

 to the conclusion that there was very little published on the bacte- 

 ria carried by insects as compared to the protozoa. I have since 

 been surprised to find how much has been done on this subject, 

 following the work of Cao. ' the Italian investigator. In fact 

 there has not been enough attention given to the results of Cao's 

 research. He found that larvae of the house fly and flesh flies 

 feeding in diseased carrion take up whatever bacteria are present, 

 at all stages of their development, that many of these bacteria 

 multiply and Bacillus anthracis even slowly forms spores in the 

 insect, that many of them are carried in the insect body through 

 all its phases of development and persist for days in the adult after 

 its maturity, contaminate its excrement daily, and are found on its 

 eggs when deposited. Thus a single fly larva breeding in diseased 

 excrement and reaching maturity may give rise to cultures of the 

 disease germs wherever it as a fly alights, contaminating the 

 breeding grounds of other flies and finally giving rise to a multitude 

 of disease-germ carriers which may bring about a sudden unex- 

 plainable outbreak of a disease thought to be latent. Cao found 

 that cockroaches could likewise take up disease germs and further- 

 more that often these bacteria acquired greater virulence by 

 passage through the roach. A long serie-. of papers by subsequent 



