118 THE SPRING GRAIN-APHIS OE " GREEN BUG. 



The junior author found that at Richmond. Lad., the adult Aphid- 

 ius would live for at least two weeks when the temperature was 

 below freezing. The parasites were taken into a warm room several 

 times during these two weeks and they would become active, but 

 when placed out of doors they would soon become numb. These 

 adults were confined, however, so that excessive moisture was 

 excluded, and they may not be able to live for so long a time in the 

 fields unprotected. 



The fact that Aphidius can during comparatively cold weather 

 remain for a long period within the body of its host, and the latter 

 give no external visible evidence of its presence, will readily account 

 for the apparent absence of the parasite from any locality for an almost 

 indefinite period: however, when the weather warms up sufficiently 

 for development of the parasite to go on. its presence readily becomes 

 apparent. For these reasons, as well as others that will be men- 

 tioned in their proper places, it is impossible to say, from a cursory 

 examination, that Aphidius is not present. 



INFLUENCE OF WINDS IX THE DISPERSION OF APHIDIUS TESTACELEES. 



As the natural suppression of an outbreak of Toxoptera is more 

 dependent upon the activity of this parasite than of any other of its 

 natural enemies, it is important to learn the extent to which the para- 

 site is able to follow its host in its spread from the South over the 

 country to the northward. 



Dispersion of Aphidius may be accomplished in two ways — first, 



as larva? in the bodies of the 

 winged host insect, where it is 

 usually invisible, and. second, 

 by being carried bodily with the 

 winds along with the host. 



By referring to Table XII on 

 page 10S. it will be observed that 

 a number of cases are there 

 recorded where individuals of 

 Toxoptera graminum which were 



-Vinged female of the spring gram-aphis, ■ • i j i j 



parasitized bv Aphidius Uttacapa. Enlarged, parasitized developed tO Winged 

 (From Webster.) j^ ^^ ^ ft period of 



eight or nine days, and during this time gave birth to young, but 

 from their dead bodies Aphidius afterwards issued. The pres- 

 ence of winged parasitized females on the leaves of grain and gra- 

 inhabited by Toxoptera is of common occurrence (see fig. 29). Thus, 

 while it has not been possible to observe the parasitism of individuals 

 and follow out the final dispersion of the same, the evidence tending 

 to show the probability of its general occurrence is so overwhelming 

 that such direct proof does not seem necessary. With the obscurity 



