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 

 affairs 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. 

 Crawford, 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 

 localities within the infested area as soon after their emergence as was 

 practicable, and as before attempts to secure laboratory reproduction 

 were made. 



All of these attempts to secure the reproduction of the parasite 

 in 1906 or in 1907 failed, since only active caterpillars of the brown- 

 tail moth or gipsy moth were used. All sorts of theories to explain 

 this were formulated, but that which seemed the most reasonable at 

 the time, namely, that the parasite did not actually reproduce upon 

 active caterpillars or pupae, but only upon inactive caterpillars after 

 the construction of their nests in the fall, could not be given an actual 

 test, since inactive caterpillars were not available. An attempt to 

 carry 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 bs present as minute larvae 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 during the winter 

 of 1907-8. A radical modification in the policy of the laboratory 

 was inaugurated at the same time, and instead of discontinuing its 

 activities during 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 were 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 



