June, '10] THOMPSOX : TACHINID PUPATION 287 



which although they have several generations annually, hibernate in 

 the pupal stage, which is in consequence much longer than in the 

 summer broods. All of these Tachinids, although they resemble 

 those of the first class in the long duration of the pupal period, differ 

 from them in that they can pupate out of earth and withstand ex- 

 fposure to aerial conditions throughout the long period of hibernation, 

 without the drying up and death of the nymph. This ability to 

 withstand adverse meteorological conditions is accompanied by and 

 undoubtedly correlated with a condition of the hibernating monph 

 verv' different from what we have described in regard to the species 

 of the first class. In these species the initial development of the 

 nymph proceeds very slowly, and by the time when low temperatures 

 arrest the vital processes it has onl}- developed far enough so that 

 the general form of the pupa is apparent, none of the appendages 

 being structurally developed. The nymphs of this sort can always 

 be recognized by their creamy white color and differ markedly from 

 those of the first class. Although the wall of the puparium formed by 

 the species of this group is often much thinner than that of the 

 puparium of Blepharipa for example, the nymph, as has been already 

 remarked, can withstand exposure to aerial conditions and success- 

 fully complete its development. How well the nymph is protected 

 against drying influences may be illustrated by the following exam- 

 ple: a puparium of Parexorista chelonice Rdi., one of the Taehinids 

 included in the first sub-division of the second class, which had 

 pupated at the bottom of a box containing masses of bro-mi-tail 

 moth cocoons from a field colony, was kept in a glass vial in the 

 laboratoiy during the winter. In early spring, as some of the other 

 puparia kept under such conditions had already produced flies, while 

 this had failed to do so, the anterior end of the puparium was re- 

 moved, without breaking the pupal exuvium, to examine the condi- 

 tion of the nymph within. As it appeared to be in fairly good condi- 

 tion, it was left in the vial, and at the time when this article was 

 written, about two months later, development had progressed to the 

 point Avhere the pilosity of the eyes, the antennae and macrochastte of 

 the front and face were perfectly developed. There is in fact little 

 doubt that the fly will shortly emerge in spite of the unusually 

 adverse circumstances with which it has had to contend. The practi- 

 cal value of this point became apparent in the work with this species. 

 As it is probably the most important European Tachinid parasite of 

 the brown-tail moth, its puparia are received here in large numbers 

 in the imported masses of brown-tail moth cocoons. The fact that 

 the Tachinid can pupate and hibernate successfully under aerial 



