586 DIPTERA. 



to feed off the crop late in the autumn, and it has also 

 been recommended to turn them into the fields ao-ain in 

 the spring, in order to retard the growth of the plant till 

 after the fly has disappeared.* Too much cannot be said 

 in favor of a judicious management of the soil, feeding 

 off the crop by cattle 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 para- 

 sitical insects, which are found to prey upon the eggs, the 

 larvae, and the pupae of the Hessian fly. Mr. Herrick 

 states,f that, in this part of the country, a very large pro- 

 portion, probably more than nine tenths, of every genera- 

 tion 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 Hymenopterous insects, similar in their habits 

 to the true Ichneumon-flies. 



The chief parasite of the pupa is the 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 Ceraphron pierces it, through the sheath of the leaf, 

 and lays an egg in the minute hole thus made. From this 



* Cultivator, Vol. IV. p. 110, and Vol. V. p. 49. 



f American Journal of Science, Vol. XLI. p. 156. 



\ It is evident, from Mr. Say's description, and from Mr. Lesueur's figures, that 

 this insect is not a Ceraphron. Neither does it belong to the genus Eurytoma, to 

 which I formerly referred it. It certainly comes very near to Pteromalus, as sug- 

 gested by Mr. Westwood; but I apprehend that it should be placed in the genus 

 Rhaphiielus of Walker, or Storthygocerus of Ratzeburg. 



