PARASITES HIBERNATING IN BROWN-TAIL WEBS. 
271 
Another importation of the hibernating nests consisting, like the 
first, of about 100,000 from various localities in Europe, was received 
the next winter and handled in the same manner as was the other, but 
a flairs at the laboratory did not run as smoothly as they might in the 
spring of 1907 at about the time when the Pteromalus were issuing. 
Mr. Titus was absent on account of sickness which eventually forced 
him to resign from his position at the laboratory, and neither Mr. 
('raw ford, who first took his place, nor the present incumbent, who 
finally assumed charge the latter part of May. was sufficiently familiar 
with the work to carry it on to as good advantage as Mr. Titus would 
have done had he retained his health. Partly on this account and 
partly on account of weather conditions which were very unfavorable 
to the issuance of the parasites, only about 40, 000 of the Pteromalus 
were reared and liberated. As before, they were colonized in various 
local it ics within the infested area as soon after their emergence as was 
pract icable, and as before attempts to secure laboratory reproduction 
WOTS made. 
All of these attempts to scenic the reproduction of the parasite 
in 1906 or in 1 ( .M)7 failed, since only active caterpillars of the brown- 
tail moth or gipsy moth were used. All soils of theories to explain 
this were formulated, but that which seemed the most reasonable at 
the time, namely, that the parasite did n<»t actually reproduce upon 
active caterpillars or pupn, but only upon inactive caterpillars after 
the const met ion of their nest s in 1 he fall, conk I not be given an actual 
test, since inactive caterpillars were not available. An attempt to 
cany the living Pteromalus adults through the summer did not suc- 
ceed, and with the death of the individuals in confinement, and the 
almost immediate disappearance of those which were liberated in the 
field, the investigations were necessarily brought to a. close. 
Meanwhile, as will be detailed later on. a Variety of other parasites 
was found to be present as minute lnrvse which hibernated within the 
still living caterpillars, and for the purpose of securing these as well 
as an additional supply of the Pteromalus, further extensive importa- 
tions of the nests of brown-tail moths were made dining the winter 
of 1007-8. A radical modification in the policy of the Laboratory 
was inaugurated at the same time, and instead of discontinuing its 
activities dining the winter months, the experiment was made of 
keeping it open for the purpose of conducting a series of winter inves- 
tigations, and the study of the hibernating caterpillars of the brown- 
tail moth and of their parasites was selected as the subject for the first 
winter's work. 
The first lot of nests arrived from abroad in December, and instead 
of awaiting the coming of spring they w ere immediately brought into 
a warmed room in the hope that the parasites might thereby be forced 
into activity. The experiment was successful. The first of the 
