224- DISEASES OF INSECTS. 
The observations of naturalists have chiefly been con- 
fined to the Hemipterous genus Aphis -, but these early 
attracted their notice. Leeuwenhoek has given a par- 
ticular and entertaining account of the proceedings of 
I. Aphidum. As soon as the little flies approached 
their prey, they bent their abdomen, which is rather 
long, between their legs, so that the anus projected be- 
yond the head ; then with their ovipositor they pierced 
the body of the Aphis, at the same time carefully avoid- 
ing all contact with it in every other part : whenever they 
succeeded in their attempt, a tremulous motion of the 
abdomen succeeded. Only a single egg is committed to 
one Aphis : when hatched, the latter becomes very 
smooth and appears swelled ; it is, however, full of life, 
and moves when touched. Those that are thus pricked 
separate themselves from their sound companions, and 
take their station on the underside of a leaf. After some 
days the inclosed grub pierces the belly of the Aphis, 
and attaches the margin of the orifice to the leaf by silken 
threads; upon this it dies, becomes white, and resembles 
a brilliant bead or pearl a . De Geer observed also an 
Ichneumon on the Coccus of the elm, 7. Coccorum h . 
Amongst the Neuropterous tribes likewise, probably 
the IchneumonidiC commit their usual ravages ; but their 
exploits, as far as I recollect, have met with no historian. 
I have a small species related to Chclonus, which a me- 
morandum made when I took it tells me was obtained 
from JEshna viatica; yet I do not remember ever tracing 
that species to its final change, so that I must have taken 
this Ichneumon from the perfect insect. It suffices, how- 
ever, to prove that this tribe is also exposed to the at- 
3 Leeuwenh. Epist. Oct. 6, 1700. De Geer ii. 869. 
'• Ibid. i. 604. 
