New York Agricultural Experiment Station. 473 



in an incredibly short time, giving birth, in turn, to female 

 young iit an equally rapid rate with their jjarents. Winged 

 females are produced from time to time, apparently as occasion 

 demands, for the dissemination of the species. These winged 

 lice fly to other food plants or to other leaves on the same plant 

 and start new colonies. This is continued during the summer. 

 In many cases the lice migrate to new food plants for a portion 

 of the summer. In the fall they may return to food plants of 

 the same species as the original. These migratory broods con- 

 sist of winged females. A generation of sexual forms, true 

 males and females, is produced sometime during the fall. After 

 pairing, each female produces one or more eggs. The eggs are 

 usually placed on the twigs near the buds. They remain dor- 

 mant all winter, hatching early in the spring into agamic females 

 which, as they start the first broods of the season, are known as 

 *' stem mothers." It will be noticed that no male insects are 

 produced throughout the season until fall. Reproduction is by 

 a process known as budding. The following forms enter into 

 the life cycle of a species during the season. The wingless and 

 winged agamic female, the sexual female, the male, the winter 

 egg and the *■' stem mother." 



The Principal Insecticides Used in Combating Plant-lice. 



These kill by contact. Internal poisons, such as Paris green 

 and London purple, will not kill plant-lice when sprayed upon 

 the leaves. The reason for this will be apparent when it is 

 remembered that these insects suck the sap from beneath the 

 surface ofthe leaf instead of devouring the leaf itself. The in- 

 secticides used for this purpose include kerosene emulsion, the 

 kerosene-water mixture, whale-oil soap, tobacco in various forms, 

 pyrethrum powder and hot water. 



Kerosene emulsion. — This insecticide may be made after the 

 following formula: 



V\'atcr 1 gallon. 



Soap, whale-oil soap preferred % pound. 



Kerosene oil 2 gallons. 



