PARASITES OF CORN APHIS. 



161 



ratural colour, green or yellow, or brown or other 

 tints, will be seen to be of a rich bro^Yn, or almost 

 black. These have been killed by the Ichneumon. 

 The female of the Aphidiiis (see Fig. 125: 5, 6) inserts 

 a single egg into the abdomen of many Aphides, one 



FiQ. 125. — 1 and 2, Corn Aphis ; 3 and 4, wingless infested specimen : 

 5 — 8, Parasite Ichneumon Flies ; all magnified, with nat. size. 



after the other, and the maggot, which hatches from 

 the egg, consumes all that is eatable, until its live 

 host is reduced to a state which will not carry on life 

 any longer. Its uninvited guest goes through its 

 changes within to an Ichneumon Fly, and presently 

 quits the hardened skin, which is distinguished, as 

 we just observed, by its colour. Sometimes every 

 Aphis on a Corn-ear is thus destroyed, and there are 

 other kinds of allied Parasite Flies which help us 

 similarly. 



One of the forms of attack which is the plainest to 

 be seen is that of the Cabbage Ichneumon Fly 

 {Microgaster glomeratus). This little Fly lays a vast 



M 



