HOST RELATIONS OF COMPSILURA CONCINNATA 17 



was received from Deering, N. H., July 30, 1915, and from them 20 



Compsilura were obtained. No other parasites were reared; and, 

 since this was the only collection obtained during 1915, there are 

 very few data concerning the species for that year. No material 

 was collected in 1916, and only 9 specimens received during 1917. 

 The species was plentiful during 1918, 1919, and 1920, being espe- 

 cially abundant in 1919. The position occupied by Compsilura in 

 its relation to this species is about the same as in A. milberti, except 

 that it is still more complicated by the presence of two native 

 tachinids (Frontina archippivora Will, and [Exorista] Zenillia 

 futilis O. S.). The hymenopteron Apanteles atalantae Pack, is pres- 

 ent in considerable numbers, but the true struggle lies between 

 the tachinids themselves. There is little to guide us in determining 

 the status of F. archippivora. From 25 collections, this species was 

 bred from but 4, and, except in the case of 1 collection, only 5 

 specimens were recovered. The exception, however, proves some- 

 what confusing, as in this instance 17 flies were reared from 16 

 larvae. Biologically, the species is distinct from the other two, its 

 method of reproduction being that of oviposition on host. The 

 writers' records indicate Anosia plexippus as its primary host, 

 although Coquillett (1 p. 15) lists it from seven others, among 

 which are two species of the genus Vanessa, Eliminating Frontina, 

 the contest narrows to {Exorista) Zenillia futilis and Compsilura; 

 and, although there were many more Zenillia reared in 1919 12 , the 

 results of the year previous were much in favor of Compsilura. 

 Parasite summaries of 1918 show five times as many Compsilura 

 as Z. futilis. The 1920 results resembled those of 1919, showing 

 but one record of Compsilura. Apparently Compsilura has the 

 worst of the argument and the explanation may lie in its biology. 

 Z. futilis belongs to the masiceratine series (species whose repro- 

 ductive habit is leaf oviposition of microtype eggs), whereas the 

 method of Compsilura is larviposition. The latter species is double- 

 brooded and has a number of hosts. In the species belonging to 

 the first series the capacity for reproduction is enormous, the uterus 

 usually containing hundreds of eggs, whereas Compsilura is far 

 less fecund. Considering the method of reproduction of the former 

 parasite, it is not surprising that it is able to work advantageously, 

 particularly in this instance, where the host is gregarious, the larvae 

 clustered together on a limited patch of nettle. Superparasitism is 

 obvious in a few of the collections but multiple parasitism is rare, 

 only one instance being recorded (Z. futilis and A. atalantae). 



Charidryas nycteis D. and H. passes the winter as a larva and at- 

 tains its full growth by the middle of June. Adults issue shortly 

 thereafter and their offspring may be found from late July until 

 the ensuing spring. The food plants are chiefly aster and goldenrod. 

 All of the collections have been small and infrequently received. 

 The species is probably of little host value, since most of the larvae 

 attain their full development so early in the spring, at about the time 

 when Compsilura emerges. 



"From 22 collections of this species, Zenillia was reared from 17 and a total of 249 

 puparia was obtained ; Compsilura was present in 6 collections only and only 20 puparia 

 were recovered. 



