INSECT ENEMIES OF EASTERN FORESTS 603 
They are marked with a dark-brown and reddish-brown pattern and 
the wings have 2 conspicuous fuscous bands. They oviposit in the host 
cocoon, laying a rather large external egg on or near the host larva. 
The parasite larva feeds externally. From 15 to 30 days are required 
for the complete life cycle during the summer months and from 1 to 4 
generations may develop in a season. The winter is spent as a mature 
larva within the cocoon of its host. Males of 1. tenellus are unknown. 
Females are invariably produced parthenogenetically, and under 
laboratory conditions Muesebeck and Dohanian reared several lines 
of females through 12 generations. 
Theronia fulvescens (Cress.) is a very polyphagous species commonly 
parasitizing a variety of Lepidoptera from New England to Oregon. 
Evenden (746) recorded it as the most important parasite of the pine 
butterfly (Veophasia menapia). Other well-known hosts from which 
it is recorded include the Douglas-fir tussock moth (//emerocampa 
pseudotsugata), the gypsy moth (Porthetria dispar), and the brown- 
tail moth (Nygmia phaeorrhoea). The adult is a striking, almost 
unicolorous yellow or brownish-yellow insect from about 34, to 1%4 
inch long. Evenden states that females oviposit on caterpillars of 
the pine butterfly which, though weakened, transform to the pupal 
stage. Other workers have described oviposition as occurring directly 
in the host pupa, and this would seem to be the more usual procedure. 
In any case the young parasite feeds internally. 
When it has finished feeding it spins a very light cocoon within the 
host pupa, and the adult 7’heronia emerges by cutting its way out. It 
spends the winter as an adult, and apparently one or more generations 
may be completed annually. Occasionally 7heronia acts as a second- 
ary parasite, but in those instances it seems to have been more a case 
of development on a parasite already present than a deliberate attempt 
to search out a parasitized pupa. Fiske (757) reared it as a secondary 
parasite of Malacosoma disstria through Ephialtes conquisitor Say, 
and the writer has reared it as a secondary parasite of Vygmia 
phaeorrhoea through the tachinid Compsilura concinnata Meig. 
Most of the species of /'phialtes are parasites of Lepidoptera, but 
E. montana Cush. is an important parasite of the hemlock sawfly 
(Neodiprion tsugae) in Oregon. Furniss and Dowden (776) stated 
that they had found that about 2.8 percent of the cocoons of NV. tsugae 
which were formed in exposed places in 1936 had been attacked by 
this species. The adult is about 54, inch long, black, with red legs 
except the hind tibia, which is black with a white annulus, and the 
hind tarsal segments, which are white at their bases and black at 
their tips. The female £. montana bores through the host cocoon 
with its ovipositor and lays an egg inside the prepupal larva. Eggs 
hatch within a few days, and the first-instar larvae float freely in 
the body cavity, spending the winter in this stage, but apparently 
more than one brood may develop during the season, for many cocoons 
collected in the field during September produced adults of 2’. montana 
that same fall. Overwintering first instars complete development in 
the spring and the adult parasites emerge early in the summer. 
Mesoleius tenthredinis Morley is an important parasite of the larch 
sawfly (Pristiphora erichsoniz) in the United States and Canada. 
It was imported into Canada from England in 1912, and liberations 
were made near Treesbank, Manitoba. Further liberations were 
