1847.] Insects Injurious to Vegetation. 13 



We therefore subjoin a brief sketch of the contents of this part 

 of Mr. Herrick's article. 



The Hessian {\y is pi'eyed upon and devoured by at least four 

 other insects. W hen its eggs are laid upon the wheat leaves, they 

 are visited by an exceedingly minute lour winged ily, (a species 

 of Platygaster,) which punctures the egg and deposites in it four 

 or six eggs of its own: the Hessian fly worm hatches, grows, and 

 passes into its flax seed state with these internal foes feeding upon 

 it: it now dies, and its destroyers in due time escape from the flax 

 seed shell. Three other minute four winged flies, or bees as they 

 would be called in common language, destroy the fly when in its 

 flax seed state. The most common of these, by far, is Say's Ce- 

 rapkron destructor. Alighting upon the wheat stalks, instinct in- 

 forms them precisely where one of these flax seeds lies concealed. 

 They thereupon "sting" through the sheath of stalk, and into the 

 body of the worm, placing an egg therein, which hatching to a 

 maggot, lives upon and devours the worm. Such are the means 

 which nature has provided for preventing this pest from becoming 

 unduly muhiplied. And so eflficient and inveterate are these 

 foes, that more than nine-tenths of all the Hessian fly larvae that 

 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. 



From the date given by Mr. Herrick of his first discovery cf 

 the egg parasite, we know that the first or autumnal generation 

 is attached by it. Whether it preys upon the second or spring 

 generation also, does not so clearly appear. From our own ob- 

 servations, and the well known habits of the other parasites, it 

 would seem to be principally upon the second or spring generation 

 which they prey. Indeed w^e can scarcely conceive it possible 

 for them wath their short ovipositors, to reach the flax seeds of the 

 first generation, buried as these are beneath the surface of the earth 

 and reposing at the roots of the young wheat. That these para- 

 sites are surprisingly abundant, and destroy immense numbers of 

 the spring generation, any one can easily ascertain by collecting 

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

 preserve all the insects which hatch from it. He will thus ob- 

 tain parasites in abundance, and only occasionally a Hessian fly. 

 On the other hand, numbers of the young plants taken up by us 

 in April, evolved nothing but Hessian flies. The observations of 

 a single season, we are aware, cannot be relied on for establishing 

 a point like this. But they force upon us the suspicion that it is 

 chiefly the second generation that is infested by parasites, and 

 that the first is comparatively free from them. 



