THE CANADIAN ENTOMOLOGIST. 79 



Canada also, Blue grass {Poa pratensis) is the most common host 

 of Toxoptera. 



The diffusion or natural spread of the Green Bug is de- 

 pendent upon a number of factors both meteorological and bio- 

 logical. For example the influence of wind in dispersion depends 

 upon whether the insect is in a winged or apterous condition and 

 this is, of course, dependent upon those factors producing these 

 conditions such as the curtailing of food supply, etc. The most 

 favourable conditions for natural diffusion appear to be a decreas- 

 ing food supply with a fairly high temperature and a not excessive 

 parasitism. 



The effects of temperature varied according to the locality 

 whether in a north or southern region. In the north, where the 

 effects of the temperature concern us most, the insect winters in 

 the egg state. Here warm winters are of less importance and 

 cool weather during spring and early summer exert a far greater 

 influence on the numerical abundance of the insect. 



As the early developmental stages in the winter eggs are 

 effected by the temperature a complete ^tudy of the biology of 

 Toxoptera necessitated the study of the embryology. The results 

 of this study and the figures of the embryonic stages which are 

 given are a welcome addition to our knowledge of insect embry- 

 ology, the observations on that peculiar embryonic structure which 

 the present authors have termed the "polar organ" being of 

 special interest. The general results of their stud} , however, does 

 not materially affect the early observations of Witlaczil, Will and 

 others and the more recent work of Tannreuther. 



The study of the natural enemies of the Green Bug naturally 

 forms one of the most important sections of the work. The efforts 

 made in certain quarters in the direction of distributing the chief 

 parasite Aphidius testaceipes Cresson (known also by a host of 

 other synonyms under the genus Lyslphlebus) and the reported 

 success of these efforts made it extremely desirable that the bio- 

 logy and distribution of this parasite should be carefully studied 

 and this fact is especially borne out by the results of the present 

 thorough study of Aphidius, its biology and its relation to meteoro- 

 logical conditions in Kansas and other States. It was found that 

 not only did this parasite occur over almost the entire United 



