91 THE SPRING GRAIN-APHIS OK GREEN BUG. 



together with that contained in the various tables and diagrams 

 relating to temperature effects upon this insect: (1) That mild 

 winters are of much more vital importance in Texas than they are 

 in the latitude of southern Kansas and northward, and (2) that the 

 influences of abnormally warm weather, if the temperature rises high 

 enough, have the effect of bringing about activity among the parasites, 

 which has a restraining effect upon the increase of Toxoptera. 



In the North, where the pest winters over wholly or largely in the 

 egg stage, warm winters are of less importance, while abnormally 

 cool weather during spring and early summer exerts a far greater influ- 

 ence. This fact renders a study of the embryology and temperature 

 effects upon eggs and stem mothers necessary to a full understanding 

 of the entire problem, extending as it does over both North and 

 South. 



The fact just stated is somewhat peculiar and was unexpectedly 

 revealed by the combined studies of those engaged in the investiga- 

 tion of the insect, and called for a study of the development of the egg, 

 which has been carried on by the junior author with the results 

 given in the following pages. The most important influence of 

 temperature is, of course, upon the development of its principal 

 natural enemy, ApJiidius testaceipes, further discussed in connection 

 with the studies of that insect. 



EMBRYOLOGY. 



Although the development of the parthenogenetic egg in Aphididge 

 has received considerable attention from several authors, that of the 

 true egg has received very little study. Hence the junior author 

 has given a limited amount of time to the study of certain important 

 phases in the development of the winter egg, as contrasted with the 

 winter condition of the viviparous insect in the South. 



Not wishing to duplicate the work of the other writers, who have 

 confined their studies for the most part to the earlier stages of develop- 

 ment, -he has begun with the formation of the blastoderm, his main 

 object being to follow the principal stages of development of the 

 embryo through the fall until growth is checked by freezing tempera- 

 tures, to note the time when growth is resumed in spring, and to 

 observe the effect of varying temperatures on development, all of 

 which has to do with the fluctuations of the insect in point of numbers 

 in the North and relates to its economic importance, besides balancing 

 our knowledge of the insect at a corresponding season in the South. 



Most of these studies were carried out at the University of Illinois 

 under the supervision of Dr. J. W. Folsom. We are deeply indebted 

 both to him and to Dr. W. M. Wheeler of Harvard University for 

 their kindly criticisms and helpful suggestions. 



