DISEASES OF INSECTS. 227 



made by M. Ameclee 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 (Ceddomyia Juniperi), 

 which forms galls upon the juniper is devoured by an 

 external Ichneumon 5 ; 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 antennae 

 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- 



a N. Diet. cTHisL Nat. xvii. 513. b De Geer vi. 41 1. 



c VOL. I. p. 172. d Linn. Trans, iv. 236. 



c VOL. I. p. 50-. 170. Since that Volume of the present Edi- 



