18 BULLETIN 539, U. S. DEPARTMENT OF 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 oar rearing cages larvae were fed cowpea leaves in test tubes 
and jelly glasess. During the first and second ins tars 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 this 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. 
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