9© Mr. CuRTls's Obfervalions on aphides. 



When plants affume a fickly appearance, or are disfigured by 

 difcafe, from whatever caufe the dileafe may arife, they are faid to be 

 bUghted. Bhghts originate from a variety of caufes, the chief of 

 which are unfavourable weather and infefts. 



Two opinions prevail very generally in regard to blights: the 

 one, that the infeds which are the caufe of them are brought from a 

 didance by eafterly winds ; the other, that they attach themfelves 

 to none but plants already fickly. Neither of thefe opinions, as far 

 as I have obfefved, is founded in faft. I am induced, from the nu- 

 merous obfervations I have made on infeds for a feries of years, (in 

 purfuing the cultivation of plants) to confider t\\Q. Aphis as by far 

 the mod general caufe of the difeafes diflinguiftied by the name of 

 blights. Other infe6ts, it is true, more efpecially the larva of fome 

 of the Lepidoplera, as thofe of the PhaUenx tortricesy disfigure and do 

 i^nfinite mifchief to plants, by rolling and curling up the leaves. But 

 thefe for the mofl part confine themfelves to certain trees and 

 plants. Their ravages alfo are of fhorter duration, being confined 

 to the growth of one brood, and they are alfo lefs fatal. It would 

 be no difficult matter for me to fill a volume .with obfervations, to 

 which I have been an eye witnefs, of the injuries which plants 

 fuftain from infefts; but that would be foreign to my prefent pur- 

 pofe, which is to fhow that the Aphis is the grand caufe of thefe 

 difeafes, and to place the modus operandi, or the manner in which 

 they effeft this bufinefs, in its true light. 



We are fully aware that certain gregarious infects may at parti- 

 cular times rife up in the air, and, if fmall and light, be impelled by 

 any wind that may chance to blow at the time; and on this prin- 

 ciple we account for that ihower of Aphides defcribed by Mr. White 

 to have fallen at Selborn. But certainly this is not the mode in 

 which thofe infefts are ufual.ly difperfed over a country. The phas- 

 nomenon is too unufual, the diftribution would be too partial ; for 



Aphides., 



