14 BULLETIN 1363, U. S. DEPARTMENT OF AGRICULTURE 



NYMPHALIDAE 



The family Nymphalidae offers the greatest number of host in- 

 sects. Species of the genera Polygonia, Eugonia, Charidryas, 

 Euvanessa, Vanessa, Aglais, and Basilarchia have all given forth 

 Compsilura. With the exception of Basilarchia and Charidryas, 

 which hibernate as larvae, the life history of these hosts is similar. 

 All except Charidryas nycteis are double-brooded, or at least have a 

 partial second generation, and are to be found in the field from early 

 spring until late fall. The larvee are, for the most part, gregarious, 

 in the early stages, at least. 



In this group are to be found the most constant alternate hosts and 

 in some respects the most favored. In percentage of parasitism the 

 rate here is as high as in any other group. In the future other 

 species of this family will no doubt be found to harbor Compsilura. 

 It is useless to speculate, however, on the host possibilities of any 

 species of a given group, for no matter how closely the hosts are 

 allied, they may be unsuitable. For instance, among the arctiids 

 we find favored hosts, such as Diaci'isia virginica and Estigmene 

 acraea, and on the other hand we find species of little or no host 

 value, such as Hyi?hantria cunea, Phragmatobia fuliginosa, and 

 Isia Isabella. 



In behavior there is some variance. Euvanessa antiopa L. always 

 remains in a colony until the time of pupation and is usually found 

 high above the ground feeding on willow, elm, poplar, and birch. 

 Eugonia j-album and Polygonia intei*rogationis do not remain gre- 

 garious for so long a period; otherwise their habits are much the 

 same. 



One of the most conspicuous examples of competitive parasitism 

 occurs in the spiny elm caterpillar {Euvanessa antiopa L.). Col- 

 lections of this species have been constant and, for one year in par- 

 ticular, abundant (Table 1). Nearly all of the larvse received were 

 in the last stage. It is doubtful whether we have any other species 

 where there are more data available for studying the relationship 

 which Compsilura bears to a single competing tachinid than in this 

 species. Material has been reared in bulk collections and as indi- 

 viduals. The results have been studied from every angle, and yet it 

 is exceedingly difficult to draw any definite conclusions. Facts ascer- 

 tained from one year's data and corroborated by a second, or in some 

 cases by a third, are contradicted by the results of the fourth. Con- 

 ditions are so entirely different each year that it is useless to attempt 

 to arrive at average results. The two tachinids playing such an im- 

 portant part in the control of this species are the native tachinid, 

 Pelatachina pellucida Coq., and Compsilura. The former has but a 

 single generation and appears to be peculiar to this host alone. 



Not the least of our difficulties in estimating value of these para- 

 sites is the great amount of superparasitism which occurs among 

 them. s This is still further complicated by a good deal of multiple 

 parasitism. 9 Nearly one-half of the collections received during the 

 eight years of study is subject to the latter phase of parasitism. It 



3 The term " superparasitism " is used to indicate that more than one parasite of a 

 single species attacks the individual host. 



9 The term " multiple parasitism " indicates that two or more different species of 

 primary parasites attack the same individual. 



