586 DIPTERA. 



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

 been recommended to turn them into the fields again 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, tlie 

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

 states,f that, in this part of the countiy, 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 Sir. Herrick. They are 

 all minute Hymenopterous insects, similar in their habits 

 to the true Ichneumon-flies. 



The chief parasite of the pupa is the Oeraphron destructor J 

 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. 



t 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 Pteromalusj as sug- 

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

 Rhaphilelus of Walker, or Storthygocems of Eatzeburg. 



