115 

 CHAPTER XXI. 



FUTURE PROSPECTS OF THE DISEASE. 



Mischief done to esculent vegetables, &c., by vastator (454). Dura- 

 tion of insect pests : historical analogies (455). Probabilities as 

 to increase of the plague (456, 457). Aphis brassicae (458). 

 Insect destroyers of vastator (459). Probable result of disappear- 

 ance of vastator (460) ; of continuance (461) ; of increase (462). 

 Concluding remarks (463). 



(454.) WE have now seen that the gangrene of the 

 potatoe is caused by the injury done to the plant by a 

 small insect which has appeared in great abundance, and 

 which attacks also the turnip, tfye beet, the carrot, the 

 different Solani, various Cruciferse, wheat, and Indian 

 corn. 



(455.) Upon examining historical records, we have also 

 found, that when an insect has appeared in great excess, it 

 has generally, after a time, disappeared, and the balance 

 of nature has been again maintained. 



(456.) In the present instance, however, although we 

 have seen whole clouds of these Aphides, although they 

 exist by countless millions, yet we are not at all in a 

 position to state that they have reached their climax. 



(457.) It is possible that they may continue for some 

 time longer, and that next year they may destroy not only 

 the various vegetables which have hitherto been their 

 prey, but may even annihilate the wheat. 



(458.) The excessive appearance of this Aphis this 

 year is not a singular fact, for the Aphis brassica exists in 

 such abundance, that thousands are to be found on the 



