19 
though the body fluids had been extracted. In every such case one 
of these parasite maggots was found in the immediate area, strongly 
indicating that the pteromalid parasite travels from one hibernating 
web to another close by, and in the course of its development con- 
sumes several caterpillars. 
Adults of these parasites have been determined as Eupteromalus 
* nidulans (Foerster), 10 a parasite of the hibernating larvae of the 
brown-tail moth which is well established in New England as a re- 
sult of parasite introduction in connection with work on the gipsy 
moth and brown-tail moth. 
The causes of the remaining 21.7 per cent mortality of the hiber- 
nating larvae are unaccounted for. Part of it may be due to mites 
which are found in considerable numbers in the webs containing the 
dead larvae. It should be noted that in the area where the observa- 
tions were made no unusual winter temperatures have occurred since 
these observations were begun. 
Mortality in New Westminster, British Columbia, due to Spicaria 
sp., a fungous disease, has been reported by Glendenning " as 
amounting to 90 per cent in the season extending from November 
to March, 1920-21, and again in 1921-22, at Vancouver and New 
"Westminister. At Nanaimo the mortality was not nearly so great. 
Climatic conditions in this section vary so greatly from those ob- 
taining in the Eastern States that mortality records are not com- 
parable. During the humid season on the Pacific coast conditions 
are very favorable for the growth of fungous diseases, and this fact 
accounts for the high mortality recorded. 
Individual egg clusters vary greatly in the proportion of eggs 
that hatch. Of the satin-moth eggs in clusters collected in the field, 
from 30 to 95 per cent hatched, the average being 80 per cent. Many 
of the larvae which hatch from eggs deposited on rocks, fences, build- 
ings, and other objects must die without finding any favorable food 
plant. Such mortality may be high in heavy infestations. 
ECONOMIC IMPORTANCE 
It is hazardous to predict the extent of injury likely to be 
caused by the establishment of a foreign insect in a new environ- 
ment. The observations made since the satin moth was first dis- 
covered in this country indicate that this insect is largely restricted 
for food to a rather limited group of trees — the poplars and willows. 
Up to the present time in the infested area most of the feeding has 
been done on trees planted for shade in parks and along roadways, 
or on trees planted for ornamental purposes on estates. Most of 
these trees are of rapid-growing varieties, and many of the small 
branches on Lombardy poplars have died after suffering severe 
* defoliation. Complete defoliation of large white poplars has caused 
the death in whole or in part of the trees attacked. In severe 
infestations the trees are defoliated, and enormous numbers of the 
large caterpillars migrate in search of food. They then become a 
nuisance, dropping on pedestrians, crawling up and down trunks of 
10 Determined by P. B. Dowden and A. B. Gahan, of the Bureau of Entomology. 
11 See p. 12 of publication cited in footnote 3. 
