INSECTS INJURIOUS TO POTATO, KTC. 



227 



from whose publications the accompanying account has been 

 compiled. The most destructive of these is known as the potato- 

 scab gnat which, in its larval or maggot form, measures about 

 one-sixth of an inch in length. It is the young of a wingless 

 female and winged male gnat or midge, somewhat like the 

 fickle midge treated in preceding pages as an enemy to cu- 

 cumber. The female deposits eggs on tubers in the cellar from 

 autunui to spring. The maggots enter old scab spots or slightly 

 injured places, and under favorable conditions a generation is 

 developed every 20 to 25 days. Later in spring the gnats 

 deposit their eggs in manure or decomposing material, on seed 



Fig. 145-— Potato scab-gnat, o. Fly; ;, larva, g, egg: h, egg mass, etc- Much 

 enlarged. (After Hopkins) 



potatoes and growing tubers in the hill, to which they may be 

 transferred on seed tubers or in decaying matter. Once within 

 the tuber and the conditions remaining favorable, the potato is 

 destroyed; but if the maggots are driven out by natural enemies 

 or the soil l^ecomes dry they disappear. The infested places 

 show nearly the same characters as ordinary scab, for which 

 malady it may be easily mistaken. The conditions most favor- 

 able to the increase of this pest are moist, damp cellars, and wet 

 weather during the warmer season. They cannot thrive in dry 

 soil or in perfectly dry storerooms. Immense loss to potatoes 

 was caused in West Virginia during 189 1 and 1892, in Phila- 

 delphia and probably in other sections of the country. Under 

 favoring conditions for their increase, the gnats may be even 



