10 



CIRCULAR 3 4 6, U. S. DEPARTMENT OF AGRICULTURE 



The larva, or maggot, is sluglike and usually has a mottled brown 

 or green color. It moves slowly about the leaf in search of food, 

 seizes the aphid prey, and sucks out the body juices. During its 

 period of development each larva may consume up to 400 aphids, 

 depending upon their size. The feeding period covers from 7 to 15 

 days. 



The completion of feeding is followed by the resting, or pupal 

 stage, during which the transformation to the adult fly takes place. 

 The puparium, which encloses the insect while it changes to the 

 adult form, is tear-shaped, brown or green in color, and is usually 

 found among the aphid colonies where feeding took place or in 

 sheltered places upon plants or on the ground. 



INTERNAL PARASITES 



The various species of aphids, or plant lice, are attacked in large 

 numbers by minute wasps, which develop within the body. The 



Figure 



An aphid parasite {Lysiplile'bus testaceipes) in the act of stinging an aphid. 

 The egg is inserted in the body at this time. X 15. 



common grain aphid known as the " green bug " (Toxoptera grami- 

 num Bond.) is often heavily attacked by one of these (Lysiphlehus 

 testaceipes (Cress.)) and under favorable conditions the pest is 

 greatly reduced, often to the point where no further damage is in- 

 flicted. In many instances, however, this control comes relatively 

 late in the season and after extensive damage has already been done. 

 The same is true of the parasites of other aphids occurring on the 

 different orchard, field, and garden crops. 



The grain aphid parasite just referred to deposits its egg within 

 the body of the aphid (fig. 6), and the adult wasp emerges 1 week 

 later. The body contents of the parasitized aphids are entirely con- 

 sumed, and the bodies assume a characteristic mummified condition 

 (fig. 7, B) and adhere to the leaf surface. At times these mummified 

 remains may be seen in enormous numbers upon the foliage; in fact, 

 in far greater numbers than the healthy individuals. The mature 

 wasps emerge from the body of the host aphid by cutting a circular 

 lid in the body wall. The fact that the parasite completes a genera- 

 tion in from 7 to 10 days and that each adult may attack a total of 100 



