46 MASS. EXPERIMENT STATION BULLETIN 189. 



stalk, in the ear or in the taproot. They do not generally spin any pro- 

 tective cocoon, but remain quiescent during the cold weather. Feeding 

 is resumed during the warm portions of pleasant days in early spring, 

 but the larva? return temporarily to their quiescent state during cold 

 nights or inclement and col4 spring weather. The hardened condition 

 of stalks and ears during the spring does not appear to present any diffi- 

 culties to them, as they tunnel through all parts of the plant with the same 

 apparent ease as when the plants were comparatively soft and green 

 the preceding season. Cobs of seed corn, which had been stored on the 

 cob all winter and were very hard and dry, contained living larvEe of 

 the borer in April, 1918. That they had been feeding during the warm 

 periods of the early spring was evidenced by the mass of frass extruding 

 from their tunnels. This occurrence will serve to illustrate the danger 

 of disseminating the pest by the transportation of corn on the cob. 



Habits when attacking Dock. 



The first instar larva of the European corn borer feeds, to some extent, 

 on the tender seed heads of the dock plant, and also upon the epidermis 

 of the leaves, but soon works its way down between the main stalk and 

 a leaf sheath. Here the first molt occurs, and the second instar larva 

 feeds on the leaf sheath, the basal part of the leaf petiole, and on the 

 small secondary stalks which arise at the junction of the leaf and the stalk. 

 Wlien the leaf petiole is tender enough the second instar larva usually 

 tunnels into it and molts into the third instar, either in this location or 

 at the base of the leaf petiole when it has been unable to effect an en- 

 trance. The third instar larva usually tunnels in the leaf petiole and 

 molts to the fourth instar within its tunnel. Occasionally the third instar 

 larva does not feed within the leaf petiole, but enters the main stalk at 

 the junction of the petiole and stalk. Normally, the larva does not enter 

 this main stalk until the fourth instar is reached. After entering the 

 stalk it usually tunnels downward through the nodes and internodes, 

 practically consuming the interior of the stalk. The remaining instars 

 are passed, and the larva becomes full grown and pupates, within this 

 tunnel. A large quantity of frass is extruded by the larva through the 

 entrance hole, and becomes webbed into the axial flowers situated between 

 the main stalk and the petiole. This accumulation of frass makes in- 

 fested dock plants very conspicuous, even before the upper portion of the 

 plant breaks over at the entrance hole of the larva. 



By the 1st of August nearly all of the dock plants are dead, so the 

 activities of the European corn borer in this plant are confined to the 

 first generation. 



Habits when attacking Lady's-thumb. 



In this common host plant of the European corn borer the first instar 

 larva tunnels directly into the main stalk at a point about 1 or 2 inches 

 below the terminal leaves. Soon after the plant is attacked it may easily 



