INSECT ENEMIES OF WESTERN FORESTS Pf 
The pupae are mottled, greenish brown, about one-half inch long, 
and are unprotected by a cocoon. The moths appear within 10 to 14 
days and during an epidemic are so abundant as to give the im- 
pression of a snowstorm in the woods. Creeks, springs, and rivers 
are covered with the dead bodies, and tree trunks are plastered with 
them until heavy rains wash them into the ground or carry them 
away. There is one generation annually. 
Outbreaks usually last for about 3 years, after which they are 
generally brought under control by the action of parasites, predators, 
and disease. Heavy 
rains during the 
flight period reduce 
egg laying, checking 
an epidemic and 
hastening its decline. 
Although nature 
will ultimately bring 
outbreaks under con- 
trol, a vast amount 
of timber might be 
saved if artificial 
control measures 
could be appled to 
from heavy defolia- 
tion. It has been 
found. that trees can 
recover from a_ 50- 
percent defoliation, 
and in some cases a 
75- percent defolia- 
tion is not fatal un- 
less the trees are sub- 
sequently attacked by 
bark beetles. At 
HIGURE 36.—Thbe oak looper (Hllopia Se a Cater presen t, airplane 
pillars on defoliated branch; B, pupae; @, adult moths, : DG 3 
female above, male below. Natural size. dusting (33, 54) of 
fers the only prac- 
tical means of controlling this defoliator on large forest areas, but 
because of high risk and cost, it can be apphed only under par- 
ticularly favorable circumstances. (See discussion on p. 178.) 
The oak looper (Zllopia somniaria Hulst) (fig. 36) is so closely 
related to the hemlock looper that some entomologists consider the 
distinction questionable. At least this probably represents a variety 
or race of loopers that shows a distinct preference for Oregon white 
(Garry’s) oak, on which it feeds in Oregon and northward into 
British Columbia. Other trees may be attacked but usually only 
when intermingled with the preferred host tree. In some seasons the 
oaks in Willamette Valley in Oregon are completely defoliated over 
large areas by this species. No permanent damage is done, how- 
ever, since the oaks are able to leaf out again the following year. 
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