During the spring and summer, the walnut caterpillars, _Datana
integerrima_ G. & R. and others, may strip the leaves from branches or
entire small trees. The adult is a moth with a wingspan of 1½ to 2
inches. The forewings are light brown with darker wavy lines. The
hindwings are lighter in color without lines.
The immature larva is reddish brown with narrow yellowish lines that
extend the length of the body. The full-grown larva is almost black with
two grayish lines on the back and two on the sides. Many long, soft gray
hairs are distributed over the body.
This insect overwinters in the pupal stage in the soil. The adult
emerges in the spring and deposits eggs in masses on the underside of
the leaves, Figure 20. The larvae feed in colonies on the leaves for
about 3 weeks. At periodic intervals, the groups of larvae move to the
trunk to molt and, after shedding their skins, they return to the leaves
to feed until the next molt. They do not encase themselves in webs.
There are two generations each year, the first appearing in late spring
and early summer, the second in later summer and fall. Larvae of the
second generation complete development and crawl down to pupate in the
soil.
_Control._—When these insects become abundant enough to defoliate
portions of the tree, they may be controlled by applying a spray
containing 2 pounds of 50 percent DDT wettable powder; 3 pounds of lead
arsenate; or 1 pound of 25 percent parathion wettable powder per 100
gallons of water.
[Illustration: Figure 20. Walnut caterpillar adults and egg mass on
a pecan leaflet.]