312 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 



may, of course, not he the case; at the present time we have no means 

 of knowing.) And thirdly, while the abundance of mosquitoes agrees 

 to some extent with the distribution of the disease, the two are not so 

 closely correlated as would be expected were mosquitoes the carriers 

 of the infection. This vn\\ be more fully dealt with on a following 

 page. 



It would appear, therefore, that while the mosquito cannot be 

 entirely ignored as a possible carrier of acute poliomyelitis, it is not 

 open to great suspicion. Nevertheless, mosquitoes should be care- 

 fully collected during an entire season and continually kept in mind as 

 a possible, but not probable, source of infection. 



Another important group of Diptera concerned in the transmission 

 of disease are various biting muscid flies commonlj^ known as tsetse 

 flies." These belong to a single genus Glossina, and, as is well known, 

 are the carriers of sleeping sickness in man and various trypanosome 

 diseases among domestic animals. They are the specific alternate 

 hosts of the various trypanosomata and thus, so far as we know, abso- 

 lutely necessary to the spread of such diseases. These flies are not na- 

 tive to America, but there is one common biting muscid, the stable fly, 

 Stomoxys calcitrans L., common to Europe and America, which is 

 very closely related to the tsetse flies, both in structure and habits. 

 It has been quite definitely associated with the spread of surra and 

 may reasonably be suspected of transmitting any disease represented 

 by organisms in the blood. As is mentioned later in this article, 

 this fly has been found in the environs of practically every case of 

 anterior poliomyelitis examined with this in view, and may quite 

 possibly prove to be the insect responsible for its spread. So far as 

 can be ascertained at the present time, the comparative abundance 

 of this fly during the summer months coincides closely with the inci- 

 dence of poliomyelitis, as the fly appears in small numbers early in the 

 summer, and persists in increasing numbers until quite settled cold 

 weather in the fall. Such a seasonal fluctuation has been observed in 

 the disease, which appears in early summer, increases toward the early 

 fall and then practically disappears during the late fall, winter, and 

 very early spring. Such increase during the course of the season is 

 not common to all insects, but is characteristic of such as have a short 

 life cycle, permitting a number of consecutive broods to mature each 

 season. It is, of course, also common to mosquitoes, house fl"es, etc., 

 although less strikingly so in the case of mosquitoes. There is some 

 discrepancy in the autumnal disappearance of the flies and the disease, 

 as the latter appears regularly to drop off a little sooner than might be 

 expected. This seems easily explainable, however, on the basis of a 

 lessened activity on the part of flies in cool weather, and the shorter 



