349 
after the completion of his report, and press of other work has prevented 
the publication of a revised edition up to the present time. The 
Department has been fortunate the present summer in being able to 
reemploy the author of the report, and his first task will be a careful 
revision of his old work, so that a new edition, brought down to date, 
will be published before the close of the year. 
Investigations of the Cause of Potato Scab and Potato Rot. — At the cel- 
ebration of the cominetion of the West Virginia Experiment Station 
building at Morgantown, April 6, 1894, Mr. A. D. Hopkins, Ento- 
mologist to the Station, presented a somewhat exhaustive paper on 
the relation of certain Dipterous larvae of the family Mycetophilidae 
to the so-called potato scab and potato rot. As the result of exten- 
sive investigations begun in the fall of 1891 and continued up to 
date, Mr. Hopkins concludes that a large percentage of the damage to 
potato tubers in West Virginia heretofore attributed to the potato scab 
fungus, Obspora scabies Thaxter, and to the potato-rot fungus, Phytoph- 
thora infestans, is caused both directly and indirectly by certain of 
these fungus gnats. He also believes that the attacks of the same 
insects are the primary cause of most forms of potato scab which are 
real detriments to the tubers. One of the forms more especially 
instrumental in producing the injurious condition referred to is an 
undescribed species to which Mr. Hopkins has given the MS. name 
Epidapus scabies and the common name, Potato- scab Gnat. He has 
ascertained that the fungus gnats which induce certain forms of potato 
scab breed commonly in soils containing decaying vegetable matter, 
animal manures, and similar substances; that lime and ashes offer 
favorable conditions for their increase, in promoting decomposition of 
vegetable matter and moisture and in presenting unfavorable condi- 
tions for the presence of insect enemies. Dry or sandy soil free from 
vegetable matter presents unfavorable conditions for the development 
of the gnats. The use of scabby seed potatoes offers favorable condi- 
tions for the attack of the insects, as these are attracted to the scabby 
spots, in which they breed, and are thus brought into contact with the 
growing tubers. Mr. Hopkins recommends soaking the seed potatoes 
in a solution of corrosive sublimate previous to planting. Fortunately 
the preventive measures found to be most effective against the scab 
fungus are equally applicable in the prevention of the attack and injury 
of the fungus gnats. 
