266 [Senate 
creatures could not have been reduced to such straits for want of the 
appropriate repository for their eggs, until after these crops have been 
utterly consumed. And, with the insect not exterminated, but still 
everywhere common, now that the culture of wheat has been gradually 
returned to with such success that it has again become general, why has 
not the fly again increased? Why have the considerable crops of the 
past and the abundant ones of the present year (1845) in this county, 
been so little injured? I am firmly persuaded, therefore, that the speedy 
diminution in the numbers of the wheat-fly, which soon follows a season 
in which it has been extremely annoying, can not be truly assigned to 
the cause above stated; but that it is rather to be attributed to that 
beautiful provision of nature long since observed, and additional 
instances of which are brought to light by the investigations of every 
year, to wit, that an undue increase in any of the species of the animal 
or vegetable world never takes place, without being speedily succeeded 
by a corresponding increase of the natural enemies and destroyers of 
that species, whereby it again becomes reduced to its appropriate 
bounds. 
Whenever once introduced, it is probable the wheat-fly will ever 
after continue in limited numbers, laying the wheat crop annually 
under a moderate contribution for its support. Isolated fields will 
occur where its devastations will be quite serious, whilst the crop of 
the district generally will suffer but little, and many fields none at 
all. Such has appeared to be its history in this vicinity for several 
years past. Seasons favorable for its multiplication will doubtless 
occur, when its injuries will be much augmented; as well as seasons 
of a reverse character, when its presence will scarcely be known. It 
is therefore very important that the entire history and habits of this 
insect should be accurately traced out. For only with a full knowledge 
of these, can we be able to resort intelligently to such measures as will 
keep its numbers constantly limited, or sweep it from those fields that 
will probably at times be excessively infested by it. 
Its habits. 
Relying upon the correctness of the published statements, that it 
was not till “towards the last of June ” that the fly infests the wheat- 
fields, and that the “principal deposit of eggs is made in the first 
half of July,” I had not commenced searching for it, when on the 
