DISEASES OF INSECTS. 291 
ing hemp; and the other, which feeds on a Boletus, that 
of a gnat?, 
The Lepidoptera, however, is the Order over Mie larvee 
of which the Ichneumons reign with undisputed sway ; 
attacking all indiscriminately, from the minute one that 
forms its labyrinth within the thickness of a leaf, to the 
giant caterpillar of the hawk-moth. The most useful of 
all, however, the silk-worm, appears, at least with us, ex- 
empted from this scourge. De Geer, out of fifteen larvee 
that were mining between the two cuticles of a rose-leaf, 
belonging to the first tribe here alluded to, found that 
fourteen were destroyed by one of these parasites, only 
one coming forth to display itself in all its brilliancy and 
miniature magnificence>. One of the most useful to us 
is that which destroys the clothes-moth, which the same 
writer also traced*. Another, equally serviceable, takes 
up its abode in the caterpillar that ravages our cabbages 
and brocoli (Pieris Brassice), which perish by hundreds 
from its attacks. As this falls frequently under our no- 
tice, it will not be uninteresting to give a fuller account 
of it. Reaumur has traced and related its whole history. 
One of these little flies that he observed, was so intent 
upon the business in which she was engaged, that she 
suffered him to watch her motions under a lens, without 
being discomposed. She pursued nearly the same plan 
of proceeding with that of the Ichneumon of the wheat- 
gnat just described ; except that she repeated her opera- 
tions frequently on the same caterpillar in different parts, 
alternately plunging im and extracting her ovipositor. 
She seemed to prefer the spot where the segments of the 
body are united, particularly where the eighth meets the 
* Ent. Carn. 760, 761. > De Geer i. 587, 
© bid. ii, 876—. 
