242 QUARTERLY JOURNAL. 



thus the insect, having no place to deposit its eggs where its young 

 could be nourished, has become measurably " starved out." But 

 that this opinion is erroneous, is I think evident from one or two 

 facts. During this entire period, since notice was first attracted to 

 the wheat-fly, there are some farmers who have every year con- 

 tinued the cultivation of wheat with very fair success, their crops 

 having been in no one of these years so severely injured as to dis- 

 hearten them ; and their respective situations are so dissimilar, that 

 this immunity can with no plausibility be attributed to any pecu- 

 liarity in the locations of their farms. Now if the swarms of these 

 insects which for a time pervaded every neighborhood through this 

 entire section of country, and which possess a power of wing capa- 

 ble of bearing them from twenty to fifty miles in a single season, 

 had been in the " starving" condition supposed, how have the fields 

 alluded to escaped destruction ? Certainly these myriads of tiny 

 creatures could not have been reduced to such straits for want of 

 the appropriate repository for their eggs, until after these crops 

 had 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 be- 

 come general, why has not the fly again increased ? Why have the 

 considerable crops of the past and the abundant ones of the present 

 year in this (Washington) county, been so little injured ? I am 

 firmly persuaded, therefore, that the speedy diminution in the num- 

 bers 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 

 the truth 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 



irs 



