'THE CANADIAN ENTOMOLOGIST. 329 



enough to justify an opinion, 22 are oligotropic and 22 polytropic. It is 

 doubtful whether a true Fanurginus occurs in America. Psetidopanurgns 

 is composed of oligotropes of Compositse. The Halictidse are among the 

 most polytropic of bees, only being surpassed by Apis and Bombus. The 

 general character of the hosts does not show that it is an important matter 

 whether the hosts are oligotropic or not. Among the Andrenidce in 

 particular, it does not appear that oligotropic species are any more apt to 

 be infested than polytropic. There is a better basis for the proposition 

 that the Strepsiptera prefer bees of small size. Pierce says : "No rela- 

 tionship can be found between the parasites and the artificial subgenera 

 designated for Andrena by Robertson." One would hardly expect them 

 to show any relation to artificial subgenera. Even if my divisions of 

 Andrenidse could be shown to be artificial, it would not follow that there 

 are no natural groups into which the species fall. The fact that Pierce 

 can only arrange the Stylopidse in the alphabetical order of their names, 

 does not indicate that they are likely to conform to any natural groups. 

 If Pierce's statements about the importance of observing the flower visits 

 of the hosts were valid, my genera would be valuable for his purpose, for 

 four of them, lomelessa, Parafidrena, Ptilaiidrena and Pterandrena, are 

 oligotropic. The preference of Strepsiptera for particular hosts does not 

 appear to be of any decisive value in determining the taxonomy of the 

 hosts. The Xenidse infest the Halictida.', and then, instead of extending 

 to the Andrenidae, which Pierce includes in the same family, they pay 

 their attentions to Vespidse, Eumenidae and Sphecidse. They even infest 

 the Panurgidse, which are more nearly related to Andrenidae than to the 

 Halictidse. Stylops seems to show a fine sense of specific distinctions, 

 but to be quite stupid in regard to natural groups. I think that if statis- 

 tics be applied to the measurements of the stylopized and non-stylopized 

 species, it will establish a strong general presumption that Stylops prefers 

 small species of Andrenidae without regard to their natural grouping. 



While it is probable that some species of Stylops limit themselves to 

 particular species of Andrenidae, there is a strong presumption that some 

 of them do not. The validity of the species can only be established by 

 the ability of the taxonomist to identify them without knowing the hosts 

 from which they come. 



Pierce's names suggest an interesting taxonomic matter which does 

 not seem to have been properly considered. This is not the only case I 

 have noticed, nor the worst, but is a fair example. To prevent endless 

 changes, a good many taxonornists have, with reason, decided that a name 



