150 ENTOMOLOGICAL SOCIETY 



derived from their existence. The larvae of these gnats act as 

 scavengers ; not only do they do away with rotting fungi, but 

 they cause these often injurious productions to putrefy and become 

 scarce by their destruction." 



There are a few records of species of Sciara inhabiting living 

 vegetable matter, but it appears that these observations have not 

 been so substantiated as to leave no doubt in the minds of Osten 

 Sacken and others regarding their correctness. Therefore, even 

 if Sciara species have frequently been met with in injuries to 

 vegetation during the investigation of such troubles, the observer, 

 after referring to the best authorities on the habits of this class of 

 insects, would more than likely fail to detect their true relation 

 to the injury, and blame it to fungi, or to some other insect inhab 

 iting the same wound. It would be natural to conclude that they 

 were present merely for the purpose of feeding in the diseased 

 and decaying matter. This, in connection with the fact that the 

 theory, with reference to insects being the cause of the potato- 

 scab, having been universally discarded, it would appear, has 

 served to remove all suspicion from the so-called fungus-gnats 

 as having anything to do with causing the blemish. 



Had I the opportunity of examining the literature with refer 

 ence to Mycetophilidse and the diseases and blemishes of potato 

 tubers when the investigations were begun, I have no doubt they 

 would have been discontinued before any important results were 

 obtained. I would have concluded, like others, that the insects 

 were merely feeding on decaying substance. As it was, I had 

 determined all of the principal facts with reference to the habits 

 of the insects and their relation to the injury before I was enabled 

 to examine any really important literature upon the subject. The 

 observations, including my own, with reference to Sciara inhab 

 iting potato tubers may be briefly stated as follows : 



At least seven species of Sciara have been bred by European 

 entomologists from what were supposed to be decaying potato 

 tubers. Mr. Walsh, when State Entomologist of Illinois, found 

 the larva of a Sciara inhabiting potato-scab, which he suspected 

 of causing the trouble. I have observed the larva of a Sciara 

 and an Epidapus feeding on the living, healthy tissue of potato 

 tubers, and have obtained conclusive evidence that they are 

 capable of causing, and actually do cause, conditions which in 

 one stage would be recognized as potato-scab, and in a more 

 advanced stage would be recognized as a form of potato-rot. 

 When we consider, in connection with these facts, that the so-called 

 potato-scab occurs in all countries where the potato plant grows ; 

 that fungus-gnats are also common in the same countries ; that 

 all of the conditions recognized as being favorable to the devel 

 opment and promotion of the scab are equally favorable for the 



