302 TRANS. ST. LOUIS ACAD. SCIENCE. 



especially when associated with difference in the cocoon, would 

 indicate specific difference. But the result of my study shows 

 very clearly that there may be great variation in the characters of 

 the cocoon, and that these are of little value in distinguishing 

 species. Indeed the color, form, texture and arrangement of the 

 cocoons varies greatly not only in the different species, but some- 

 times in the same species. The same species of caterpillar also 

 often suffers from the attacks of several species of Microgasters, 

 as is the case with the Army-worm ; and, conversely, one species 

 of Microgaster often attacks a variety of caterpillars, and in this 

 case the species sometimes presents slight variation in its charac- 

 ters when attacking different hosts. This variation may be con- 

 sidered entomophagic, and when sufficiently marked should be 

 indicated by a variety name, as I have done below in treating of 

 Apatiteles congregatus. The species Apattteles cassiaiivs bred 

 from Tei'ias nicippe shows a peculiar variation in the cocoon 

 and also in the time required to perfect the imago. Its cocoons 

 are either yellowish, ovoid, and quite woolly; or brown, four-sided, 

 and without loose silk. Cocoons of the two forms found with 

 the Terias on Cassia tnarylandica Sept. lo, iS74,gave forth flies 

 on Oct. ist following and on Aug. 4th, 1S75, the former from the 

 ovate cocoons, the latter from the other form of cocoon, and the 

 flies are indistinguishable. 



From the cocoons of Microgasters are often bred secondary 

 parasites. The most common of these are either Ichneumonids 

 of the genera Hemiteles and Mesochorus^ or Chalcids allied to 

 Pieromahis. The Hemiteles cressonll bred by me from the 

 galls of Gelechia galhesolldaglnls is probably a parasite of the 

 Microgaster which attacks the maker of the galls. Mesochorus 

 vltreus Walsh, which was described as a parasite of the Army- 

 worm {Leucanla unipunctd)^ I have bred from the Microgasters 

 truly parasitic on that pest. The Chalcid, Glyphe vlrldesce?ts 

 Walsh, which was bred by Walsh from Apanteles militarise 

 and by Fitch (who, in his 9th Report, described it as new under 

 the name Pteromalus tabacum) from Apanteles congregatus 

 when parasitic on the Tobacco-worm {Macroslla qulnque-macu- 

 lata), I have bred from the last named Apanteles when parasitic 

 on the Army-worm. 



