INSECTS INJURIOUS TO SMALL GRAINS 



155 



" As further illustrative of the important bearing of weather 

 conditions, it is found that in the case of the three important out- 

 breaks of this insect, namely, for the years 1890, 1901, and 1907, 

 the temperature for the first five months of each of these years, 

 including the latter part of the winter and spring, was above the 

 normal for the winter months and below 

 the normal for the spring months; in 

 other words, warm winters and cold, late 

 springs." 



" The little parasitic wasp which is so 

 useful in the control of this pest is native 

 to this country, widely distributed, and 

 every year does its work with the ' green 

 bug ' and with other aphides. It is 

 always present in grain fields, as shown by 

 its appearance every year, to war on these 

 pests whenever the weather conditions 



FIG. 115. Dead "green 

 bugs," showing hole 

 from which the matu- 

 red parasite of Lysiph- 

 lebus emerges. The 

 top figure shows the 

 lid still attached, but 

 pushed back; the bot- 

 tom figure shows the 

 parasite emerging. 

 Enlarged. (After 

 Webster, U. S. Dept. 

 Agr.) 



FIG. 114. Lysiphlebus parasite in act of depositing 

 eggs in the body of a grain-aphis much enlarged. 

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



make its breeding and multiplication possible, and its rate of breed- 

 ing is so rapid (there being a generation about every ten days) that 

 with a week or two of favorable weather it gains control over its 

 host insects and destroys them." * Extensive experiments were 

 'conducted in Kansas in 1907 in importing these parasites from 



* From F. M. Webster, Circular 93, Bureau of Entomology, U. S. Dept. 

 Agr. See also Bulletin of the University of Kansas, Vol. IX, No. 2, by 

 S. J. Hunter, The Green Bug and Its Natural Enemies. 



