140 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



the aphids migrate to various grasses, being particularly fond of 

 Kentucky blue-grass, and may subsist on corn, on which they 

 may feed until oats and wheat are available in the fall. Oats is the 

 favorite food, and outbreaks of the pest have always been worst 

 where volunteer oats is generally grown, the aphids increasing 

 on it in the early fall and winter and later spreading to wheat. 

 By October 15th in Minnesota and by early November in Kansas 

 the true winged males and wingless egg-laying females have been 

 observed, but strangely enough they have only been secured in 

 small numbers by being reared in the laboratory, and have not 

 been observed in the field, so that although these females laid eggs 



FIG. 120. Lysiphlebus testaceipes Cress., adult female and antenna of male 

 greatly enlarged. (After Webster, U. S. Dept. Agr.) 



freely on the leaves of grain, we do not know whether they are 

 essential or not to the life history of the insect in the field, for 

 while the eggs are being produced other females continue to give 

 birth to live young until the cold of winter, and they have been 

 observed to reproduce with a daily mean temperature barely 

 above freezing. 



Natural Control. The natural control of this most destructive 

 pest involves a most interesting relationship between temperature 

 and development of the parasites which check its development. 

 " The ' green bug ' in normal years that is, when its breeding 



