136 



INSECT PESTS OF FARM, GARDEN AND ORCHARD 



but later migrate to volunteer oats and wheat, upon which they 

 subsist until fall wheat is available. Owing to the cool weather 

 of fall and the fact that but few individuals survive the attacks 

 of their parasites during the summer, they rarely become abundant 

 enough to do any damage to grains in the fall. So far as known, 

 they hibernate over winter among the leaves of the growing plants, 

 enough surviving both snow and cold to 

 infest the crop the next spring. Whether 

 true males and females produce eggs on 

 the grain is unknown, for though they have 

 beenreared under artificial conditions, 

 they have never been observed in the field. 



FIG. 1 16. Grain a p h i d s 

 clustered on wheat head, 

 greatly enlarged. (After 

 Weed.) 



FIG. 117. Wheat-louse parasite (Aphidius 

 avenaphis Fitch), and parasitized louse 

 from which it has issued. (Copied from 

 J. B. Smith.) 



Professor F. L. Washburn observed at least fourteen generations 

 up to November 8, 1907, in southern Minnesota. 



As with other aphids, both winged and wingless individuals 

 occur throughout the season. The wingless individuals are 

 about one-tenth inch long, with black antennae as long as, or longer 

 than the body, are of a yellowish-green color, often slightly 

 pruinose, and long black nectaries extend from either side of the 

 abdomen. The winged individuals are about the same length, 

 with a wing expanse of about three-eighths inch, with antennae 



