449 



Aphis inaidimdicis. the so-called corn root-aphis, is not especially dif- 

 ferent in adaptive characters from the other root-lice generally, and it 

 lives, indeed, in early spring on plants extremely unlike corn. Finding 

 its first food on sniartweed (Polygonum) and on the field grasses ( Se- 

 taria. Panicum. etc.), it is scarcely more than a piece of good fortune 

 for it and for its attendant ants if the ground in which it hatches is some- 

 times planted to corn, in which it finds a more sustained and generous 

 food-supply than in the comparatively small, dry and slow-growing plants 

 to which it would otherwise be restricted. 



The larva of Diabrotica loiigicornis. usually known as the corn root- 

 worm, is, of course, well constructed to burrow young corn roots, but it 

 differs from related Diabrotica larvae in no way that I know of to sug- 

 gest a special adaptation to this operation except in the mere matter of 

 size. If it were larger it would probably eat the roots entire, as does the 

 closely related and very similar larva of D. 12-pnnctata. Indeed, there is 

 some reason to believe that D. longicornis may breed in large swamp 

 grasses, since the beetle has been found abundant in New Brunswick in 

 situations where it is difficult to suppose that it originated in fields of 

 corn and where such grasses are extremely common. Even the special 

 corn insects seem, in short, structurally adapted to much more general 

 conditions than those supplied by the corn plant alone, and if they are 

 restricted largely or wholly to this plant for food, this seems due to other 

 conditions than those supplied by special structural adaptations. 



In short, in the entomological ecology of the corn plant we see noth- 

 ing whatever of that nice fitting of one thing to another, specialization 

 answering to specialization, either on the insect side or on that of the 

 plant, which we sometimes find illustrated in the relations of plants and 

 insects. The system of relations existing in the corn field seems simple. 

 general and primitive, on the whole, like that which doubtless originally 

 obtained between plants in general and insects in general in the early 

 stages of their association. 



Such adaptations to corn as we get glimpses of are almost without 

 exception adaptations to considerable groups of food plants, in which corn 

 is included — some of these groups select and definite, like the families of 

 the grasses and the sedges to which the chinch-bug is strictly limited, and 

 others large and vague, like the almost unlimited food resources of the 

 larvje of Lachnosterna and Cyclocephala under ground. These are evi- 

 dently adaptations established without any reference to corn as a food 

 plant, most of them very likely long before it became an inhabitant of our 

 region, and applying to corn simply because of its resemblance, as food 

 for insects, to certain groups of plants already native here. 



Entomological Ecology of Corn .\nd the Str.xwberrv 



Corn being, in fact, an exotic or intrusive plant which seems to have 

 brought none, or at most but one,' of its native insects with it into its new 



^ Diabrotica longicornis Say. 



