DISEASES OF INSECTS. 227 
made by M. Amedee Lepelletier upon its history have 
not yet been given to the public 3 . 
Dipterous insects, likewise, do not escape from these 
pests of their Class: but few observations, however, have 
been recorded as to the species assailed by them. We 
learn from De Geer, that a gnat {Cecidomyia Juniperi), 
which forms galls upon the juniper is devoured by an 
external Ichneumon 15 ; that which injures the wheat in 
the ear, whose ravages I formerly mentioned to you c , af- 
fords food to three of these parasites, — one I lately men- 
tioned as probably devouring its eggs ; another pierces 
the glumes of the floret, where its destined prey is con- 
cealed ; and the third enters it. I once placed a number 
of the larvae of the gnat upon a sheet of paper, at no 
great distance from each other, and then set down one 
of these last Ichneumons in the midst of them. She be- 
gan immediately to pace about, vibrating her antennas 
very briskly : a larva was soon discovered, upon which 
she fixed herself, the motion of her antennae increasing 
intensely ; then bending her abdomen obliquely under 
her breast, she inserted her ovipositor, and while the 
egg was depositing these organs became perfectly mo- 
tionless. The larva when pricked gave a violent wriggle. 
This operation was repeated with all that had not al- 
ready received an egg, for only one is committed to each 
larva. I have often seen it mount one that was already 
pricked, but it soon discovered its mistake, and quitted 
it untouched d . The Hessian Fly also {Cecidomyia De- 
structor) related to the preceding, whose alarming ra- 
vages I formerly described to you e , has a peculiar para- 
3 A r . Diet. d'Hist. Nat. xvii. 513. b De Geer vi. 41 1— . 
c Vol. I. p. 172. '' Linn. Trans, iv. 236. 
* Vol.. I. p. 50 — . I/O—. Since that Volume of the present Edi- 
2 2 
