CORN INSECTS 219 



dandelion, pepper-grass, toadflax, mild water pepper, cockle- 

 bur, vervain, common nightshade, skullcap, Teucrium laciniatum, 

 Leptochloa filiformis and Mentha arvensis. 



The corn root-aphis has been studied most carefully in 

 Illinois. The insect passes the winter in the egg stage in the 

 care of a little brown ant, Lasius niger americanus Emery. 

 The ants tend the aphids in much the same way as man cares 

 for domestic animals, being very fond of the sweetish liquid, 

 known as honeydew, secreted by them. This aphis has become 

 so dependent on the ants for the care of the winter eggs and for 

 placing the young lice on the roots of their food plants that they 

 would doubtless all perish were there no ants present to attend 

 them. The eggs are stored in the ants' nest, where they are 

 protected by the workers as carefully as are the young of their 

 own species. Sometimes in warm days in early spring, the 

 ants carry the eggs to the upper galleries of the nest or even 

 lay them out in the sunshine and carry them back at night. 

 This is probably done in order to keep the eggs in good condition 

 and to hasten their hatching. In central Illinois the eggs begin 

 to hatch in early April, just as the smartweed, pigeon-grass and 

 ragweed plants are coming up. The young aphids are carried 

 by the ants and placed on the roots of these weeds. Here they 

 are attended by the ants, whose burrows are extended to include 

 the roots. The young aphids pass through four nymphal stages 

 in the course of their growth and reach maturity in about 

 nineteen days, on the average, in Illinois. As the eggs hatch 

 over a considerable period, usually from early April to the last 

 of May, the last nymphs hatched will find themselves surrounded 

 by representatives of three generations. All the individuals 

 of the first generation are wingless but in the later generations 

 there is a varying percentage of winged forms produced. The 

 latter occur in greatest numbers when the roots are crowded 

 and food is scarce. The winged forms leave the roots, come 

 to the surface and take flight, seeking new feeding grounds. 



