96 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



reason to believe that others among the introduced species will not 

 disperse at an equal rate, once they are sufficiently well established. 



But Monodontomerus is eminently well fitted for dispersion, and 

 its case is altogether different from that of a tachinid which is de- 

 pendent upon sexual reproduction for the continuation of the spe- 

 cies. A few hundred individuals, spreading rapidly toward all 

 points of the compass, soon become widely scattered, and it is, and 

 will remain for a long time, a question just how rare an insect may 

 be and each individual still be able to find its mate. That the indi- 

 viduals of the first colonies of many of the tachinid parasites scat- 

 tered so widely as to make the mating of the next generation purely 

 a matter of chance and of rare occurrence is now accepted as well 

 within the bounds of probability. 



The first serious doubts as to' the wisdom of the policy of the small 

 colony were felt in 1907, and beginning with June of that year. larger 

 colonies were planted in the instance of every species than had been 

 the practice up to that time. In the fall of 1908 the recovery of 

 Monodontomerus over a wide territory lent strength to these half- 

 formed convictions, and when, during 1909 and 1910, one after 

 another of the various parasites were recovered under circumstances 

 which were in most cases essentially similar, all doubts vanished as 

 to the wisdom of the course finally adopted. At the present time 

 there is no more inexorable rule governing the conduct of the labora- 

 tory than that establishment of a newly introduced parasite is first 

 to be secured, while dispersion, if later developments prove that it 

 can be artificially aided, comes as a wholly secondary consideration. 

 For the most part, however, dispersion may be left to take care of 

 itself. 



An even larger appreciation of the necessity for strong colonies 

 has been reached during the present winter (1910-11), coincidently 

 with the results of the scouting work for Monodontomerus and 

 Pteromalus in the brown-tail moth hibernating nests. (See maps, 

 Pis. XXII, XXV.) The details will not be given in this imme- 

 diate connection, but they will be found later on in connection 

 with the discussion of these species. It is sufficient at this time to 

 say that the circumstances under which the Pteromalus was recov- 

 ered after the lapse of two years following its colonization were such 

 as to cast doubts upon the conclusions which had been tentatively 

 reached concerning the inability of certain other species to exist in 

 America, and their possible significance had something to do with 

 the decision to continue the work of parasite importation along 

 wholly different lines in 1911. It may be, after all, that 40,000 

 individuals of Apanteles fulvipes are not enough to make one good 

 colony. 



