376 AGRICULTURE OF MAINE. 



corolla of certain flowers guide them to the nectary; though 

 we do not see why the scent is not in the main sufficient for 

 this purpose. According to Sir John Lubbock, "The visits of 

 insects are of great importance to plants in transferring the 

 pollen from the stamens to the pistil. In many plants the sta- 

 mens and pistil are situated in separate flowers; and even in 

 those cases where they are contained in the same flower, self- 

 fertilization is often rendered difficult or impossible; sometimes 

 by the relative position of the stamens and pistil, sometimes by 

 their not coming to maturity at the same time. Under these 

 circumstances the transference of the pollen from the stamens 

 to the pistil is effected in various ways. In some species the 

 pollen is carried by the action of the wind ; in some few cases, 

 by birds; but in the majority, this important object is secured 

 by the visits of insects, and the whole organization of such 

 flowers is adapted to this purpose." 



Parasitic Insects (Ichneumons and Tachina:). — While insec- 

 tivorous birds accomplish much towards reducing the numbers 

 of injurious insects, they often as likely as not eat the beneficial 

 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. 



