Ohfervations on the IleJJian Fly, 03 



kinds of bearded wheat will foon reduce diem to an inconfi- 

 derable number ; but that bearded wheat alone will not have that 

 good effe6l unlefs it be attended with the circumflance of being 

 fown late ; and that the idea which has been prevalent in 

 many parts of the country, that there exifts fome principle in 

 the nature of the infe6l itfelf, which will caufe it to decline, or 

 wholly difappear, in any particular place, after it has prevailed 

 there for three fucceffive years, is an opinion which experience 

 has fhewn to be erroneous j and that the better opinion is, how- 

 ever unfavorable it may be to the profperity of our country, 

 that the changes to which the fpecies is fubjeft with refpeft to 

 number, can only arife from unfavorable feafons, or from the 

 want of proper food for fubfillence. When this infeft firfl 

 began to prevail in the manner as above related, I confidered it 

 as a matter of importance to afcertain its nature and mode of 

 propagation, and the number of generations it pafTed through 

 in a year, and in the two years above mentioned, in which it 

 proved fo generally deftruftive to wheat, I made a variety of 

 experiments and ohfervations on that fubjecl ; and firom fome 

 of thefe, I was at firft inclined to fuppofe that there might be 

 three generations of the infe6l in a year; but afterwards, upon 

 further examination, it appeared fufficiently evident that there 

 could be but two ; and in this opinion I have been more fully 

 confirmed, fmce I have had an opportunity of making repeated 

 examinations into the nature of the infeft in the laft year. The 

 refult of thefe ohfervations has been, that the Heffian Fly is an 



