190 



adopted. Steeping the seed is of course useless as regards our 

 insect, and probably every other, except so far as it contributes 

 to tlie vio'or of the plant. If immediately after the wheat is 

 reaped in July, the stubble is burnt, and then plowed in and 

 harrowed, the insects then in the pupa state would be destroyed. 

 If this were done universally, we . might extirpate tlie insect. 

 But it never will be done to any great extent. Feeding off the 

 young plants while the eggs are on the- leaves would destroy 

 vast numbers, and would not much retard the growth of the 

 wheat. 



The parasites cut off a large portion of every year's genei-a- 

 tion. In this region of country I am safe in saying that on this 

 account principally, not one egg in fifty prodvices a Hessian 

 Fly ; but the destruction comes too late for that season, as it does 

 not take final effect until the insect assumes the state of pupa. 



I have observed four parasites. 1st. A species of Platygas- 

 ^er which attacks the eggs. 2d. The Eurytoma (not Gerapliroii) 

 destructor of Say, which attacks the pupa ; this is the princijial 

 parasite of the pupa. 3d and 4th. Insects of the tribe Chalcididce 

 or Oxyuri. 



HERBICK TO HARRIS. 



April 24, 1841. 



On looking at your former letter, I find a question which I 

 think I have never answered. The puparium (pupa-case) of 

 the Cecidomyia destructor^ which is of a brown color and leath- 

 ery texture, is formed from the skin of the larva ; this skin 

 gradually becomes brown, the pvipa (or larva changing to pupa) 

 gradually cleaves off from this skin, and in two or three weeks 

 is wholly detached. This is the fact regarding the larva of the 

 0. destructor; but nine-tenths of all, which one may chance to 

 examine will contain a parasitic larva. It was a long time be- 

 fore I could distinguish them with certainty. 



