6 Farmers’ Bulletin 1169. 
NATURAL CONTROL OF SHADE-TREE INSECTS. 
One of the forces which affects insects adversely or otherwise is 
the weather, this depending upon whether it favors the host tree or 
the insect. Directly engaged in 
checking undue multiplication of 
any given insect are parasitic 
plants (fungi and bacteria), birds 
and other vertebrates, spiders, 
mites, and insects. The insect 
enemies of insects are usually the 
most powerful and _ effective 
agency in the reduction of a nox- 
ious insect. All stages of an in- 
sect, from egg to adult, are subject 
to their attack. These insect ene- 
mies operate in two ways, accord- 
ing to their build and_ habit. 
Some of them are predacious, in 
that they seize their prey and eat 
it either by sucking it dry or by 
devouring it bodily (fig. 1). 
Ladybirds are among our best 
friends among predacious insects. 
=== Plant-lice or aphids particularly, 
Fic, 1 Catenion of sins 0 (Per ut also seale bugs and other soft 
soma beetle, Calosoma sycophanta. bodied insects, are to their liking. 
(Burgess and Collins.) Their active young as well as 
adults feed on these insects. Lace-wing flies, numerous bugs, and 
certain mites and spiders are among the other recognized predacious 
insects man has 
learned to regard 
with favor for their 
active feeding on 
injurious insects. 
The other group is 
known as parasitic 
insects (figs. 2, 3). 
These are by far 
the most numerous 
in variety B Fig. 2.—Sphinx caterpillar bearing cocoons of small, four- 
5 zl y, winged wasplike parasite. (Quaintance and Siegler.) 
special adaptations 
some of them are capable of prodigious multiplication and their pres- 
ence has again and again been found to have saved plants from de- 
struction in situations where man, left to his own devices, was helpless. 
