65 
to the natural course of events. The cottony maple scale is ex- 
tremely subject to parasites and attacks of other insect enemies, 
particularly to the black hemispherical ladybugs and their larvae, the 
latter of which feed upon the egg masses in spring and summer 
With an extraordinary abundance of the scale insects themselves 
Pig. 66. Male of Cottony Maple Scale, Pulvinaria vitis: a, adult; 
b. c. antenna and leg enlarged; d, e, second stage of pupa and its 
cast skin; /, g, true pupa and its cast skin. All greatly enlarged. 
these insect enemies improve the opportunity for unusual multiplica- 
tion in a way to produce a greater number than can possibly be 
maintained permanently by the scale insects. A check is thus put 
upon the increase of the latter which, within a few months, may re- 
duce them to insignificance. The consequence is an irregular peri- 
Fig. 67. Cottony Maple Scale. Pulvinaria vitis. 
{Adult female in spring, just before the forma- 
tion of the cottony egg sac. Enlarged. 
odicity in the numbers of the cottony maple scale such that two years 
of injurious abundance rarely succeed each other in the same place. 
Nevertheless, where trees are evidently suffering from the scale at- 
tack it is always prudent, and often necessary, to take artificial 
measures of protection. 
