‘ 
300 THE ENTOMOLOGIST. 
the females; however, in Ratzeburg’s interesting ‘ Krankenge- 
schichten’ (Nos. 4 & 5) several species are mentioned as appearing 
from April to June; these were from Trachea puiperda, from 
which Ratzeburg bred twenty-six to twenty-eight different 
ichneumons. Another possible rule is that the time of appearance 
of the parasite is about the same as that of its host. We know 
that a larva exhibits little or no sign of being affected when a 
species of this family is the preyer; it is not so in many other 
cases of ichneumon parasitism. If a full-fed larva or pupa be 
more sluggish or of a darker colour than usual, or if it does not 
emerge at the proper season, it probably contains a parasite. In 
no known instance does the host of Ichnewmon die till it becomes 
a pupa; hence the emergence of a parasite belonging to this genus, 
or even family, instead of the lepidopterous imago, is frequently 
quite unexpected. The Jchnewmon pupa invariably, we believe, 
lies with its head in the same direction as that of its host, whose 
pupa-skin is filled with a thick fluid which varies in consistency 
and colour—yellowish or greenish; this surrounds the naked 
Ichnewmon pupa, and in some species the whole abdomen of the 
pupa is filled with the fluid. After emergence the affected pupa 
may easily be recognised. In the usual metamorphosis of the 
lepidopteron the pupa is ruptured on the thorax, and the wing- 
cases invariably broken along the antenne; where an Ichnewmon 
has emerged these are entire, the pupa-case being opened with a 
clean transverse cut just below the eyes; sometimes the anterior 
part is cut quite off, but more often a portion of the pupa-case is 
unsevered, whether dorsal or ventral seems immaterial. A 
detailed description of the larva and pupa of J. pisorius is given 
by Ratzeburg (‘Die Ichneumonen,’ i1., 131), who tells us he was 
well acquainted with those of many species. 
Every available authority has been consulted for the compilation 
of the following list of Ichnewmon hosts, but its accuracy cannot 
be fully relied upon, from the difficulties of identification and 
errors of synonymy. ‘I'he species are numbered as in Marshall’s 
Catalogue; the author of the biological information is quoted in 
each instance, the name being given in Roman letters after the 
name of the ichneumonized insect; those Lepidoptera not now 
known as British are marked with an asterisk. 
