EGG PARASITES OF THE BROWN-TAIL MOTH. 257 



Three races or species have been reared from the eggs of the brown- 

 tail moth, two of them being European and the third American. 

 The American, according to Mr. A. A. Girault, to whom the series of 

 mounted individuals was submitted for determination, is the com- 

 mon and widely distributed Tricliogramma pretiosa Riley. One of the 

 European, which is here referred to as the pretiosa-like form, is or 

 appears to be structurally identical with the American pretiosa. It 

 differs in that the progeny of parthenogenetic or unfertilized females 

 is either of both sexes, or else exclusively female, while the progeny 

 of unfertilized females of the American species has always been 

 exclusively male in the very considerable number of reproduction 

 experiments with such females which have been carried on at the 

 laboratory. 



The other European species may at once be distinguished from either 

 of its congeners by its dark color, as well as by other characters of 

 taxonomic value. Like the American race of T. pretiosa which was 

 studied at the laboratory, it produced males exclusively as the 

 result of parthenogenetic re- 

 production. 



It seems to the writer that 

 in the two morphologically 

 identical but biologically dis- 

 tinct races of Tricliogramma FlG . 5 s.-E gg s of the brown-tail moth, a portion of 



( T. pretiosa, American Or Ell- which has been parasitized by Trichogramma sp. 



ropean) we have what is noth- 

 ing less than two species, quite as distinct as are the species of 

 bacteria, for example, which are founded upon cultural characters. 

 If the manner in which a bacterium reacts when cultivated upon 

 a certain medium prepared after a fixed formula may be considered 

 as sufficient to separate it specifically from an otherwise indis- 

 tinguishable form which reacts in a diiferent manner under identical 

 circumstances, why may not the same distinctions be made to apply 

 to insects ? It may not appeal to the taxonomist and student in 

 comparative insect morphology, but it certainly will appeal to the 

 economic entomologist, who has, or ought to have, a greater interest 

 in the biological than in the anatomical characteristics of the subjects 

 of his investigations. The case of Tricliogramma is by no means 

 unique. That of Tachina mella, which is practically indistinguishable 

 from T. larvarum but which reacts differently in its association with 

 the gipsy moth, is another. Another is to be found in the American 

 and European races of Parexorista chelonise. There are also others, 

 which need not be mentioned here, but which will receive attention, 

 it is hoped and intended, at some future time. 



These statements concerning the behavior of the several forms of 

 species of the genus Tricliogramma are based upon the results of 



5)5077°— Bull. 91—11 17 



