THE WHEAT-FLY. 



The female lays her eggs by means of a long re- 

 tractile tube, which unsheaths an aculeus as fine as 

 a hair, and very long. 



These insects would soon become of serious in- 

 jury to mankind, were not their race kept within 

 due bounds by several natural enemies, some of 

 which devour them, and others (Ichneumon TipuU) 

 deposit their eggs in the larva?, the young of which, 

 when hatched there, find a proper nourishment in 

 the bodies of their hosts. 



This Ichneumon is about the size of the Wheat- 

 fly : and in order to observe the manner of the fe- 

 male's depositing her eggs in the caterpillars -of the 

 Wheat-fly, Mr. Kirby placed a number of the latter 

 on a sheet of white paper, and then set an Ichneu- 

 mon down in the midst of them. She soon disco- 

 vered one of the larva? ; when vibrating her an- 

 tenna? in an intense degree she fixed herself upon it, 

 and, bending her abdomen obliquely under her 

 breast, inserted her aculeus into the body of her vic- 

 tim, (which seemed by its motion to experience a 

 momentary pain,) and there deposited a single egg. 

 This being done, she went to a second, which was 

 constrained to undergo the like operation, and so 

 on to all the rest. She never deposited more than 

 one egg in each larva j and when she was remarked 

 to mount one that had been pricked before, she 

 soon discovered her mistake and left it. 



The size of the two insects is so nearly alike that 

 one young only can be nourished by a single larva ; 

 and therefore instinct teaches the parent Ichneumons 

 to deposit only this number in each. 



