18 BULLETIN 539, U. S. DEPARTMENT OP AGRICULTURE. 



thereby weakening them to such an extent that very little pressure 

 is required to break them off, and frequently infested plants break 

 off at this point when attempts are made to pull them up. 



Cowpea plants have been found almost completely cut in two, at 

 a point near or slightly below the surface of the ground, by the 

 larvae girdling the stem, while in other cases the larvae were found 

 tunneling into the stems as in the case of corn and sorghum. 1 



It is seldom that larvae are found in the tunnels of the plants upon 

 which they feed, but more often in specially constructed tubes which 

 lead away from the entrance to the tunnel in the stalk, lying even 

 with or slightly beneath the surface of the ground or sometimes 

 curved around the stems. Plate II, figures 1 and 2, shows the tubes 

 attached to the stems at the entrance to tunnels. These tubes are 

 often 2 inches or more in length and have a number of side galleries 

 or chambers (PL III, fig. 1). They are composed of particles of 

 sand and dried excrement of the larvae spun together with silk. 

 They are generally rather delicate and fall to pieces unless handled 

 with great care. The larvae apparently use these tubes as a means 

 of retreat when disturbed while feeding. 



In young corn and sorghum not more than two larvae have been 

 found feeding on one plant, each from within a separate tube, and 

 in cowpea plants never more than one. In older corn and sorghum 

 as many as 6 larvae have been found feeding at one time on the same 

 plant and 13 cocoons taken from the surrounding soil. Dr. Forbes 

 (24) reports that as many as 13 larvae have been found feeding on a 

 single corn plant. 



In our rearing cages larvae were fed cowpea leaves in test tubes 

 and jelly glasess. During the first and second instars the larvae 

 have a habit of partially skeletonizing the leaves, devouring the 

 epidermis of one side and the mesophyll, leaving the epidermis of 

 the other side intact. They construct on the leaf delicate tubelike 

 coverings made up of dried excrement spun with silk and feed from 

 under this covering. After the second instar the larvae begin to 

 eat the leaves, perforating them and devouring all except the mid- 

 veins. They persist in skeletonizing the leaves even when almost 

 mature, and tins is especially noticeable when given leaves that are 

 somewhat tough or whose tissues have hardened. The boring habit 

 (PI. Ill, fig. 3), so characteristic of the work of the larvae in stalks, 

 was demonstrated even while the larvae were feeding upon leaves, the 

 larvae even in their earlier stages boring into the larger veins of the 

 leaves and petioles and constructing tubes leading away from the 

 entrance to the tunnel. This habit was discontinued in the last stages, 

 the larvae feeding as do those of most Lepidoptera. 



1 Dr. Chittenden (22) makes mention of this method of feeding and illustrates it with a figure. 



