432 INSECTS INJURIOUS TO VEGETATION. 



much cannot be said in favor of a judicious management of the 

 soil, feeding off the crop by catile in the autumn, and burning 

 the stubble after harvest ; a proper and general attention to which 

 will materially lessen the evils arising from the depredations of 

 this noxious insect. 



Fortunately our efforts will be aided by a host of parasitical in- 

 sects, which are found to prey upon the eggs, the larvae, and the 

 pupae of the Hessian fly. Mr. Herrick states,* that, in this part 

 of the country, a very large proportion, probably more than nine 

 tenths, of every generation of this fly is thus destroyed. One of 

 these parasites was made known by Mr. Say, in the first volume 

 of the " Journal of the Academy of Natural Sciences of Phila- 

 delphia" ; and the interesting discovery of three more kinds' is 

 due to the exertions of Mr. Herrick. They are all minute Hy- 

 menopterous insects, similar in their habits to the true Ichneu- 

 mon-flies. The chief parasite of the pupa is the Eurytoma de- 

 structor (^Ceraphron destructor, of Say), a shining black four- 

 winged fly, about one tenth of an inch in length. This has often 

 been mistaken for the Hessian fly, from being seen in wheat- 

 fields, in vast numbers, and from its being found to come out of 

 the dried larva skin of that fly. In the month of June, when the 

 maggot of the Hessian fly has taken the form of a flax-seed, the 

 Eurytoma pierces it, through the sheath of the leaf, and lays an 

 egg in the minute hole thus made. From this egg is hatched a 

 little maggot, which devours the pupa of the Hessian fly, and 

 then changes to a chrysalis within the shell of the latter, through 

 which it finally eats its way, after being transformed to a fly. 

 This last change takes place both in the autumn and in the follow- 

 ing spring. Some of the females of this or of a closely allied 

 species of Eurytoma come forth from the shells of the Hessian 

 fly, without wings, or with only very short and imperfect wings, 

 in vi'hich form they somewhat resemble minute ants. Two more 

 parasites, which Mr. Herrick has not yet described, also destroy 

 the Hessian fly, while the latter is in the pupa or flax-seed state. 

 Mr. Herrick says, that the egg-parasite of the Hessian fly is a 

 species of Platygaster, that it is very abundant in the autumn, 



* " American Journal of Science," Vol. XLI., p. 156. 



