16 
We have just called attention to the fact that there were two spring 
periods of abundance in the emergence of the adults, viz, from March 
9 to 26 and from April 10 to 20. The significance of this apparent 
periodicity is not that it means the development of a second genera- 
tion, but that there occurred late in March and early in April, 1896, a 
cold spell which interrupted the issuing of hibernating individuals. 
As a matter of fact, there was no appropriate food for the development 
of an abundant generation of the parasite at this time of the year, 
since the tussock-moth eggs were only just about to hatch and other 
possible hosts hibernating as half or full grown larvie or as pup were 
not abundant. 
The exact length of time which the parasite remains in hibernating 
quarters is longer, perhaps, than would be anticipated, as is indicated 
by the fact that a number of the early March individuals, and, in fact, 
all of those which issued up to and including the 9th of this month, 
came out of cocoons collected September 6, 1895, thus giving a resting 
period of practically six months. Those issuing later than March and 
in April emerged from cocoons taken from the trees in the spring of 
1896, but which were spun the previous September and October. 
It will be noticed that a number of specimens issued during Novem- 
ber. Whether these individuals successfully hibernated in the adult 
condition or whether the occurrence of a warm sunshiny day induced 
them to oviposit in hibernating pup of the Orgyia (and we know 
from observations that, although the spun-up larva is their favorite 
condition of the host, they will often oviposit upon pup) is a matter 
which we have not decided from exact observation. We know that cer- 
tain Ichneumonids do successfully hibernate as adults and that there 
is this possibility with this species. It is safe to say, however, that 
the normal hibernating condition is that of the larva after its cocoon 
has been spun. 
All the hibernating cocoons examined were readily distinguished by 
a closer, tougher, and more parchment-like consistency. There was 
less of the more loosely: spun outer silk, although there was usually 
more or Jess of this looser silk surrounding apparently the whole mass 
of Pimpla cocoons in any given Orgyia cocoon. 
The breeding season of the insect at Washington, then, extends from 
April to October. We have shown that a single generation may be 
produced in fifteen days, and with plenty of larval food in the proper 
condition there would be a possible development of about ten annual 
generations. As a matter of fact, if we were to consider the Orgyia 
as its sole food the development of the possible early generations at 
least would be sadly interfered with by the lack of hosts. The cater- 
pillars of the first generation do not begin to spin up before Juiy, and 
the confusion of generations of the host insect, owing to the retarda- 
tion in development of some individuals and the acceleration in others, 
does not begin to take place in any marked degree until after this 
