PARASITES OF GIPSY-MOTH CATERPILLARS. 197 



within 25 miles of Boston. If it is thus generally distributed, very large numbers in 

 the aggregate may exist, and it may increase at a rate as rapid as that of Monodonto- 

 merus, and at the same time escape detection until the summer of 1911 or 1912. * 



There is not very much to add to the account given above, further 

 than the statement that all attempts to recover the species in the 

 field in 1910 from the vicinity of colonies of the year before failed. It 

 hardly seems likely that so conspicuous an object as the cocoon 

 mass of this parasite should escape the notice of the many field 

 men who are familiar with its appearance, and who know of the 

 great interest and importance which would attach to its discovery. 

 In consequence the failure to recover the species is of more signifi- 

 cance than the failure in the instance of any other parasite which 

 could be mentioned. 



At the same time all hope has not been given up, especially in 

 consideration of the curious circumstances which will shortly be 

 described, surrounding the recovery of Pteromalus egregius as a para- 

 site of the brown-tail moth. If, as can no longer be doubted, a minute 

 and to all appearances an inactive insect like Pteromalus has dis- 

 persed over a territory of approximately 10,000 square miles within 

 five years as the extreme limit, and if during that period it remained 

 so rare as to defy all of our efforts to recover it, it is not impossible 

 that Apanieles fulvipes will do the same. Should this come about, 

 the year 1911 or 1912 would probably witness its sudden and simulta- 

 neous appearance throughout the greater part of the territory infested 

 by the gipsy moth. 



It must be confessed, however, that hope rather than faith has 

 dictated these last lines. It is believed, and not without some foun- 

 dation, that the failure of Apanieles fulvipes to exist here is due to the 

 absence of an absolutely necessary alternate host, and that further 

 attempts to introduce it will be unavailing. That is the reason why 

 the most will be made of every opportunity to determine the truth 

 or fallacy of the European records which accredit it with attacking a 

 variety of insects representing half a dozen families, and two or three 

 times that number of genera, many of which are represented by 

 closely allied and sometimes by the same species in America. If 

 investigations uphold the truth of these records, no expense ought to 

 be spared in further attempts to establish the parasite in America, 

 because of all those which attack the gipsy moth it is the one which 

 was not only the most promising at the beginning, but which remains 

 the most desired at the present time. 



1 The occurrence of the cocoons in the near vicinity of the colony sites immediately following the libera- 

 tion is most natural, and in perfect harmony with the wide dispersion. The female parasites as soon as 

 they emerge are ready to deposit a small part of the eggs which they will eventually deposit if they live and 

 have opportunity. After the deposition of this part, it is necessary for them to wait an appreciable time 

 before they are ready to deposit any more. 



