March, igio] BrUES : PARASITIC HyMENOPTERA. 11 



of injurious species, and its application to various parasitic types is 

 of value in presaging the feasibility of introducing certain types. 

 With reference to the insects under consideration the Evaniidce and 

 Stephanidse appear as the most unlikely forms to adapt themselves 

 to a changed environment, and of the two much larger related fami- 

 lies, the Braconidae and Ichneumonidae, the former is for at least one 

 reason the less promising. As I have pointed out in a previous paper 

 ('lo), it gives evidence of having been more abundant in the past, 

 thus representing a somewhat decadent type. Among the several 

 divisions of the Ichneumonidae, the Pimplinse appear to be decreasing 

 in abundance although there is no doubt that some recent species are 

 very plastic to judge from their adaptation to a large series of quite 

 different host species. The Ophioninae were very abundant in the 

 Miocene and have materially decreased in number since that time, 

 while the Ichneumoninse, Cryptinae and Tryphoninae show no de- 

 crease. Prototrypoidea are not on the ascendent, but Chalcidoidea 

 and Cynipoidea appear to be very markedly so, and the increasing 

 abundance of the chalcidoids, in connection with their ability for 

 rapid increase, suggests them as eminently suitable for experimental 

 introduction. 



Another factor entering into the practical use of parasitic species 

 is the general character of the present faunae of the various geo- 

 graphical regions, and a mention of the slight paleontological evidence 

 bearing on this matter may not be amiss. It must, however, be borne 

 in mind that a more complete knowledge of fossil insects might easily 

 reverse conclusions drawai from such necessarily fragmentary data. 

 The presence of Indo-Australian types in Baltic amber of Oligocene 

 age has been recently noted by Wheeler ('08) among ants, and I have 

 recognized the same tendency among parasitic Hymenoptera, so that 

 at least some of the present types of this region show a primitive 

 or synthetic character and we should not expect to find them adap- 

 tive. This is of course merely a repetition of conditions long known 

 to exist in the vertebrate fauna of this region. Besides this rather 

 positive evidence entomology can at present offer nothing in this 

 line additional to what has been discovered from the investigation of 

 the higher groups of animals. 



