30 WHEELER— THE PARASITIC ACULEATA. 



succeeded in finding austriaca in the United States and surmises 

 that it may here be a parasite of V. consohrlna, " which, although 

 very different in coloration, is very probably the American race or 

 subspecies of Vespa rufa L." A good account of what is known of 

 the habits and distribution of austriaca may be found in the papers 

 of Robson (1898), Carpenter and Pack-Beresford (1903) and Be- 

 quaert. This wasp is so closely related to V. rufa that Carpenter 

 and Pack-Beresford regard them as a single species, and the aus- 

 triaca queen as producing both rufa and austriaca offspring. Their 

 reasons for this assumption are, however, too weak to invalidate 

 the view of the great majority of authors who hold that austriaca 

 bears the same relation to rufa that Psithyrus does to Bomhus. 

 Both arctica and austriaca lack the worker caste and eliminate the 

 queens of the colonies which they enter. Males of the host species 

 sometimes develop in colonies infested by austriaca, so that, unlike 

 Psithyrus and the workerless ants, this parasite seems not to destroy 

 the eggs laid by the host workers. 



In conclusion I would record a few reflections that have been 

 suggested by the foregoing survey of the various Aculeate parasites. 

 The tables show in a rather imposing manner that many of these 

 parasites have arisen from their respective host genera, but apart 

 from such forms as Psamuiocharcs pcctinipcs, Vcspa austriaca and 

 some of the parasitic bees like Percsia and Eucondylops there is 

 little evidence among existing parasites of a direct derivation from 

 their host species. This is what we might expect, for in the first 

 place the origin of most of the parasites is so remote that even if 

 they had remained permanently associated with the species from 

 which they arose, both host and parasite would by this time have 

 diverged in structure to such a degree that their genetic afilinities 

 would no longer be clearly discernible, and in the second place, 

 many parasites are probably no longer associated with their original 

 hosts, which have become nearly or quite extinct, so that their para- 

 sites have been compelled to adapt themselves to new hosts or cease 

 to exist. Under such circumstances a parasite would naturally 

 attach itself to a species more or less closely allied to its primitive 

 host. 



That this has been the course of parasitic evolution seems to be 



