66 MAINE AGRICULTURAL EXPERIMENT STATION. 



as well as the destructive kinds. Without doubt the leading 

 factor in preventing the undue increase of noxious insects are 

 the parasitic kinds belonging to certain dipterous and hymenop- 

 terous families. 



An ichneumon-fly (figs. 46-49) lays its eggs either on the 

 outside of the caterpillar or bores under its skin inserting an 

 egg within the body. The larva of the ichneumon upon hatch- 

 ing works its way into the interior of the host. Here it does 

 not injure the muscles, nerves, or the vital parts of the cater- 

 pillar, but apparently simply lies motionless in the body-cavity, 

 absorbing the blood of its host. 



Tachina (Senometopia) militaris has been observed by Riley 

 to lay from one to six eggs on the skin of the army-worm, "fas- 

 tening them by an insoluble cement on the upper surface of the 

 two or three first rings of the body." The young maggots on 

 hatching penetrate within the body of the caterpillar, and, lying 

 among the internal organs, absorb the blood of their host, caus- 

 ing it finally to weaken and die. Sometimes but a single mag- 

 got lives in its host. Many grasshoppers as well as caterpillars 

 are destroyed by them. 



Insectivorous Insects. — There are very many carnivorous 

 kinds which devour insects entire. Such are the ground-beetles 

 (fig. 51), water-beetles, the larvse of Tenebrionids and of lady- 

 beetles (Coccinella) (figs. 52, 53), and those of the lace-winged 

 flies (Chrysopa) which prey on aphids, thovgh the maggots 

 of the Syrphus flies are more abundant and efficacious as aphid 

 destroyers in Maine. 



Practical Application. — When the life of an injurious insect 

 is carefully studied, it is frequently found that the pest can be 

 combated by breeding and distributing its natural parasitic and 

 predaceous enemies. For a most remarkable example of such 

 an undertaking it is only necessary to mention the work of the 

 U. S. Government and Massachusetts against the Gypsy Moth. 

 For current accounts of this work the reader is referred to the 

 Annual Reports of the Mass. State Forester, and publications 

 of the U. S. Bureau of Entomology. 



