HOST RELATIONS OF COMPSILURA CONCINNATA 15 



varies in degree from year to year and is shown by the following 

 examples : 1 larva gave 1 Compsilura and 1 Pelatachina ; 1 larva gave 

 3 Compsilura and 1 Pelatachina; 1 larva gave 5 Compsilura and 1 

 Pelatachina; 1 larva gave 2 Compsilura and 2 Pelatachina; 1 larva 

 gave 1 Compsilura and 2 Pelatachina. 



From material reared in bulk, 61 larva? gave 67 Compsilura and 75 

 Pelatachina; 100 larvae gave 69 Compsilura and 15 Pelatachina; 52 

 larvae gave 70 Compsilura and 29 Pelatachina; 80 larvae gave 7 

 Compsilura and 107 Pelatachina. 



The aggregate of superparsitism far exceeds that of multiple 

 parasitism. Individual rearings have shown as many as 4 Pelata- 

 china to a single host and with Compsilura as many as 6 per host. 

 Other collections from which Pelatachina alone was reared furnish 

 striking examples of this sort of parasitism; 5 larvae gave 15 Pelata- 

 china; 89 larvae gave 90 Pelatachina. 



There are similar records for Compsilura, some of which are as 

 follows : 8 larvae gave 23 Compsilura ; 10 larvae gave 50 Compsilura ; 

 41 larvae gave 108 Compsilura. 



The presence of a hymenopterous parasite (Hyposoter n. sp.) 

 makes the problem still more intricate. Frequent rearings of this 

 species were obtained during 1915 and again in 1919. In 1921, five 

 cocoons were obtained and from these adults were secured in the 

 spring of 1922. This species hibernating in its cocoon is one of the 

 most difficult to rear to the adult stage. 



The conclusions drawn from the records of the writers indicate 

 that the presence of Compsilura is not detrimental to any great ex- 

 tent to the native tachinid. It is realized, of course, that there is a 

 considerable amount of duplicate parasitism and that the native 

 tachinid may suffer somewhat through the aggressiveness of Comp- 

 silura. On the other hand, the records show that Pelatachina 

 emerges at least two weeks and, in most instances, three weeks before 

 Compsilura; it is no doubt owing to this fact primarily that it is 

 able to compete successfully with the introduced parasite. It is 

 probable that during this period, while its attack is unhampered, its 

 effectiveness is most pronounced and that by the time Compsilura 

 appears the development of its progeny has progressed to such a de- 

 gree that it is in no way affected by that species. Furthermore, the 

 fact that Pelatachina is single-brooded and has never been recovered 

 from the collections of Euvanessa antiopa made in summer months 

 adds much to the credit of Compsilura. The records show that the 

 most that can be expected from this species (Pelatachina) is its 

 check upon the first generation ; and, as the host species may be found 

 in the field up to October, .it would therefore be allowed to increase 

 without restraint as far as that species is concerned were it not for 

 Compsilura. 10 



Polygonia interrogationis Fab. is an excellent host. It is of little 

 economic importance, and is usually found in small numbers on the 

 elm. In New York, it is somewhat injurious to hop vines but is be- 

 lieved to be held in check by the chalcis fly Pteromalus vanessae 



10 Collections received from places outside the Compsilura territory, made during a 

 period of two years, aggregate over 1,000 larvae. From these collections Pelatachina has 

 frequently been reared, but on two occasions only has any other tachinid been obtained. 

 This species, Phorocera claripennis Macq. (two individuals reared), is of apparently little 

 importance in its relation to E. antiopa. 



