7 
Insects of Shade Trees and Their Control. 31 
LEAF-CHEWING INSECTS. 
GENERAL. 
The life of the deciduous tree attacked by leaf-chewing insects is 
directly endangered by them only when they keep the tree in a state 
of complete defoliation for several years in succession. Fortunately 
this condition can apparently be brought about only by recent insect 
pest immigrants before our native predacious and parasitic insects 
develop an appetite for them. This was true not so many years ago 
of the elm leaf-beetle, for instance, which is only an occasional and 
local pest at present owing to the effective work of predacious bugs 
that feed on its eggs. Nevertheless, aside from disfiguring the tree 
for the season, defoliation tends to reduce its vitality more or less, 
and this often leads to its attack by other insects, principally bark 
and wood borers, which are much harder to combat and the injury 
of which not infrequently results in fatalities among trees. For 
these reasons, as well as the fact that it is the most easily done, it is 
advisable, wherever practical considerations permit, to check de- 
foliation as soon as observed. As not every hole in the foliage 
necessarily indicates the presence of a defoliator this point is best 
first definitely ascertained before the labor and expense of spraying 
are undertaken. Municipalities, however, should always be prepared 
for such emergencies by having on hand the necessary machinery 
and supplies for a prompt, thorough, and quick job. 
BAGWORM.” 
Recognition of work.—Although arboryite and other evergreens 
are the favorite food of the bagworm, broad-leafed trees and shrubs 
are not infrequently discovered to have their foliage eaten and bear- 
ing rough looking, more or less spindle shaped bags up to 2 inches 
long (fig. 17). On closer examination a head and six legs are found 
protruding from the opening at the upper end of the bag. Badly 
defoliated trees during the dormant season are bespangled with such 
bags, although at that time most of these contain eggs instead of 
caterpillars, 
Habits and seasonal history.—The bagworms attain full growth in 
the District of Columbia toward the end of August, whereupon they 
transform to pup. About three weeks later these change into adult 
moths, of which the females are wingless and do not leave the bag. 
The males alone emerge from the bags and fly in search of females, 
with which they mate. Immediately thereafter the female begins 
laying her eggs, with which she nearly fills her old chrysalis skin in 
the bag, wriggles out of it, and dies. The eggs thus laid pass the 
2 Thyridopteryx ephemeraeformis Haworth. 
