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Insects of Shade Trees and Their Control. 5 
GENERAL LIFE OF INSECTS. 
Like other living objects, the insects we encounter are the offspring 
of parents that preceded them—males and females in most cases. 
Between the time of hatching from the eggs and maturity the grow- 
ing insects molt, or cast off their skins, three or more times. In some 
forms, as in the aphids and bugs generally, these immature stages 
differ little from the adults. In others, as in the beetles, moths, etc., 
the immature insects, or larva stages, as they are called, differ radi- 
cally in appearance from the adults, and there is, besides the egg, 
another nonfeeding stage or form, known in moths and butterflies as 
the chrysalis and in all of them as the pupa. The pupa or chrysalis 
stage immediately precedes that of the adult. The larva of the moth 
or butterfly is generally known as a caterpillar, that of the beetle as 
a grub, that of the fly with two clear wings as a maggot, and that of 
the fly with four clear wings as a grub, slug, or false caterpillar. 
These forms generally differ sufficiently among themselves for fairly 
ready assignment to the proper group. Any one of them, except the 
egg and pupa, may be the injurious form or the one in which the 
given insect is most advantageously fought; the two—the injuring 
form and the one treated—not necessarily always being the same. 
Intelligent control of insect injury, therefore, involves at least a gen- 
eral knowledge of the habits of insects. Among these none is more 
important than the feeding habit, since this determines largely the 
control measures to be adopted. 
MANNER OF INJURY AND PARTS OF TREE AFFECTED. 
In the great majority of cases the mouth of the injurious form of 
the insect is adapted for feeding either by sucking the sap of the 
plant (plant-lice or aphids, scale insects, etc.) or by biting off bits 
~of the leaf, bark, or wood (caterpillars, slugs, beetles and their 
grubs, etc.). The work of the biting insects usually can not be 
mistaken and, in the case of those feeding on the outside of the host, 
is often a guide to the remedy, even when the insect is not caught in 
the act of eating. The sap-sucking insect, on the other hand, must 
be discovered and its identity or at least the group or family to which 
it belongs ascertained beforé the most suitable remedy can be deter- 
mined. 
Injury by either group of insects is manifested in many different 
ways. Thus, the fine rootlets may be eaten up and the larger roots 
barked or bored; the trunk and larger branches may be tunneled or 
their sap sucked ; the twigs may be deformed or cut off; the buds and 
leaves may be deformed ; the leaves may have pieces bitten out of them 
or they may be skeletonized or mined. Some kinds of insects make 
their home and feed on a large variety of plants; many other kinds, 
however, utilize only one part of one kind of plant for sustenance. 
