July 39, 1918 
Parasites of the Brown-Tail Moth 
203 
first stage within the body cavity of its host. So far as the writer has 
been able to determine, M. versicolor hibernates only in the brown-tail- 
moth caterpillars in New England. 
When dissections were being made of hibernating brown-tail-moth 
larvae in late winter, partly developed eggs of M. versicolor were often 
found, and the writer at first supposed that the species occasionally 
might go through the winter in this way. But later it was observed that 
always, when such an egg is found in a hibernating brown-tail-moth cat¬ 
erpillar, there occurs with it a first-stage larva of A . lacteicolor . The latter 
was evidently there first, and was able to prevent the complete develop¬ 
ment of the egg of M. versicolor , perhaps through the secretion of some 
toxic substance which killed the embryo. That the embryo is actually 
dead can usually be determined on close examination, provided that 
development has gone sufficiently far. 
LATER ENDOPARASITIC STAGES OP METEORUS VERSICOLOR 
In the spring when the brown-tail-moth caterpillars begin feeding the 
larvae of M. versicolor within some of them also become active, and after 
from 10 to 14 days the cocoons of the parasite appear. Development 
of the larva is not as rapid as in the case of A . lacteicolor , for the feeding 
of the parasite does not prevent the host from molting once in the spring. 
The first-stage larva of M. versicolor attains a total length of about 
2 mm. and passes into the second stage about 3 days after resuming 
activity. The second-stage larva no longer possesses the brown, heavily 
chitinized head capsule and the strong curved mandibles; the mandi¬ 
bles, or what correspond to the mandibles (Pi. 22, D), are exceedingly 
difficult to find, not being chitinized. The anal appendage, too, is no 
longer so much in evidence. The length reached in this stage is about 
4 mm., and the duration of the stage is about 4 days. The third stage, 
extending over a period of from 2 to 3 days, differs from the preceding 
stage principally in that the mandibles are chitinized, the anal appendage 
is reduced to a short spur, and the size is slightly larger. When full grown 
(PI. 21, E) the parasite measures 5 to 6 mm. in length, is cylindrical, and 
yellowish. It does not kill its host before emerging, as does A . lacteicolor , 
but leaves the latter to writhe for 24 hours or more. 
COCOOK OE METEORUS VERSICOLOR 
Unlike A. lacteicolor , the larva of M. versicolor does not begin spinning 
at once on issuing from its host, but commonly crawls some little dis¬ 
tance along a twig or branch and then, suspending itself by a strong 
thread, which it has spun and made secure, forms its cocoon, which is 
elongate-oval but somewhat attenuated at both ends, and brown. 
Within the cocoon the head of the parasite is directed downward; the 
excrement which accumulated during endoparasitic life is pushed to the 
upper end about 36 hours after spinning has ceased, and a day or two 
