300 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



or Paris green as soon as they are a few inches high. The spray 

 should be applied liberally so as to give the plants a distinct 

 coating of the mixture. Tomatoes are particularly susceptible 

 to injury and might be dipped in arscnate of lead when planting, 

 using 1 pound to 10 gallons of water. The destruction of the 

 weeds upon which the larvae commonly develop is obviously 

 important in preventing their multiplication. 



Where injury by the larva? is done to the tubers, it is recom- 

 mended that they be dug as soon as possible, and be left 

 exposed to the sun for a few hours after digging so as to harden the 

 skin, before being stored. If damage continues in storage, the 

 tubers may be fumigated with carbon bisulfide, as recommended 

 for grain insects (page 57). 



Potato-scab and Insects 



That certain forms of what is commonly termed " potato- 

 scab " are due to the work of insects has frequently been shown. 

 In 1895 Professor A.D. Hopkins,* of the West Virginia Agricultural 

 Experiment Station, reported some very careful original investiga- 

 tions upon two species of gnats, Epidapus scabies Hopk. and Sciara 

 sp., the larvae of which had been conclusively shown to cause 

 a " scab " upon the tubers by boring into them. The Iarva3 

 or maggots of the Potato-scab Gnat are about one-sixth of an 

 inch long, and are the young of a wingless gnat shown, very 

 great'y enlarged, in Fig 219. The females deposit their eggs on 

 the potatoes in storage from autumn to spring, and the maggots 

 hatching from them enter old scab spots or injured places. Under 

 favorable conditions a generation may be developed in twenty 

 to twenty-five days. Later in the spring the eggs are deposited 

 in manure or other decomposing material, on seed potatoes or 

 on growing tubers to which they may be carried on seed potatoes. 

 When they become w r ell established in a potato, it is soon des- 

 troyed if they are not overcome by their natural enemies, or 

 unless the soil becomes dry, when they soon disappear. In- 



* A. D. Hopkins, Special Bulletin 2 (Vol. IV, No. 3) W. Va. Agr. Exp. 

 Sta., p. 97. 



