148 On the Hessian Fly. 



cess is finished by the 15th or 18th of September, though 

 some of them changing from the chrysahs state later than 

 others, will lay their eggs later in proportion. 



Now, having traced the insects through one genera- 

 tion, which lasts from the latter end of April, to the 15th 

 or 20th of September, I will carry my remarks through 

 another generation, which being done, I shall have traced 

 them through their various transformation and economy 

 for the period of one year. 



From the 1st to the 20th of September the flies are 

 laying their eggs on the leaves of the young wheat, 

 which are in a few days hatched, and the young cater- 

 pillars creep down the leaf to its junction with the head 

 of the plant, which is mostly a little below the surface of 

 the ground : here they fix themselves as has been before 

 treated of. 



In that situation the caterpillars advance to their full 

 growth, so that when very cold weather begins, they have 

 changed into the chrysalis state, in which they continue 

 during the winter, fixed in the same situation at the head 

 of the young plant ; in the spring following perforate the 

 case of the chrysalis, and come forth in the fly state, in 

 April, in the latter end of the same month and beginning 

 of May, as has been before stated : this completes the 

 second generation, which lasts from the middle of Sep- 

 tember to the beginning of May following. 



To plan the periods of their generations and several 

 changes in a clearer point of view, I will in a few words 

 recapitulate what I have before stated. 



First generatioji, 



1796. 1st. The eggs were laid the latter end of April, 

 and beginning of May. 



2d. In a few days the eggs were hatched, and the 

 young caterpillars appeared in May. 



