THE HESSIAN FLY. 59 



venting this pest from becoming unduly multiplied. And so ef- 

 ficient and inveterate are these foes, that more than nine-tenths 

 of all the Hessian fly larvae that have come into existence are 

 probably destroyed by them, Mr. Herrick thinks, and we have 

 strong reasons for believing that his estimate is within the 

 truth." 



97.. It has been suggested that it is principally the second or 

 spring generation upon which the parasites prey. The immense 

 abundance of these parasites is easily ascertained by collecting 

 the infested straw at harvest time, and securely enclosing it to 

 preserve all the insects which hatch from it. Parasites in abun- 

 dance will be obtained, and only occasionally a Hessian fly ; 

 whereas young plants taken up in April by Dr. Fitch, evolved 

 only Hessian flies. The observations of a single season are not 

 considered sufficient to establish a point like this, but coupled 

 with the apparent difficulty of the short ovipositors of the para- 

 sites reaching the flax-seeds of the first generation at the first 

 joint of the plant, and consequently under the* surface of the 

 earth to a slight extent, favours the suspicion that the second 

 generation is chiefly infested by parasites, and the first compara- 

 tively free from them.- This supposition appears quite in ac- 

 cordance with the operations of other agents limiting the pro- 

 duce of the first generation, for they have all the vicissitudes of 

 a long winter, and the changeable atmospherical conditions of 

 spring, to overcome. 



ON THE MEANS THAT HAVE BEEN ADOPTED IN ORDER TO 

 LESSEN THE RAVAGES OF THE HESSIAN FLY. 



98. No one, even remotely familiar with insect economy, and 

 the admirable purposes these minute creatures are designed to 

 fulfil in preserving a proper equilibrium .between the vegetable 

 and animal world, will suppose that any remedy, properly so 



