64 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



Among the bacterial pathogenic organisms transmitted by 

 insects are those causing bubonic plague, anthrax, and typhoid 

 fever. They represent, as far as the insect intervention is con- 

 cerned, both accidental and obligatory hosts. 



As is well known many of the striking diseases transmitted by 

 insects are caused by protozoan parasites, among them malaria, 

 sleeping sickness, nagana, leishmaniasis and numerous trypano- 

 somiases. In these cases the usual function of the insect is that 

 of a necessary intermediate host to permit the development of 

 the causal organism through a certain stage. However, it is 

 evident that mechanical transmission may occur in certain cases. 

 Among the nematodes, species of Filaria are conspicuous ex- 

 amples of pathogenic organisms transmitted by insects. In addi- 

 tion to the human disease caused in this way there is filiariasis 

 of dogs caused by Filaria immitis transmitted by certain mos- 

 quitoes, and it is altogether likely that other diseases of this 

 class will be discovered in the course of time. We may also 

 mention the probable occasional dissemination of Necator by the 

 house fly and the recent work of Fibiger which shows an apparent 

 connection between a nematode carried by cockroaches and car- 

 cinomatous lesions in the internal organs of mice. The work is 

 not all complete, but, nevertheless, may be said to be extremely 

 suggestive of a possible new class of diseases in which the insect 

 may be concerned. 



Among the cestodes there are cases of the occurrence of insect 

 intermediate hosts. Among them is the disease of dogs caused 

 by Diphlydium caninum which is transmitted by fleas. The pre- 

 cise agency of flies in the transmission of the eggs of human ces- 

 tode parasites has not been made altogether clear although nu- 

 merous laboratory experiments show that such eggs are frequently 

 devoured by flies and discharged in a viable condition. As a 

 matter of fact the house fly and other species seem to have a rather 

 special predilection for the eggs. What remains in this connec- 

 tion is to determine the extent of feeding on cestode eggs under 

 natural conditions, but the laboratory experiments and the known 

 habits of the house fly leave little doubt on this score and show 

 clearly the facility of the dissemination of such eggs when devoured 

 by flies. 



It will be seen from the foregoing that insects are directly con- 

 cerned in the transmission of diseases caused by organisms ex- 

 tending over four groups from the bacteria through the protozoa 

 and the nematodes to the cestodes. 



The diversity of the insect transmitters from a taxonomic 

 standpoint is interesting. Examples are found in the mites in 

 two families of ticks and in four orders of insects proper, namely 

 Diptera, Hemiptera, Siphonaptera and Siphunculata. Even the 



