INSECT PESTS 165 



recorded by Webster and Philips : ^ The 

 dispersion of Aphiduis may be accom- 

 plished by the larvae in the bodies of the 

 winged aphids whence it is carried from 

 place to place and also by the wind. 

 While the young larvae are within the 

 body of the aphis they are not easily de- 

 tected. It is only when the larva becomes 

 nearly full grown that it may be detected, 

 and then only by an expert observer. 

 There may be millions of larvae of Aphiduis 

 in a field and yet present no visible indi- 

 cation of their presence. A few warm days 

 bring about their final development, 

 whereupon the presence of the leathery 

 brown bodies of the parasitized aphids be- 

 gin to attract the attention. Climatic con- 

 ditions are important factors in determin- 

 ing the abundance of Aphiduis. 



^ Webster, F. M., and Philips, W. J., The spring grain 

 aphis or "green bug." U. S. Dept. Agr. Bur. Entom. 

 Bull. 110, 1912. 



