! 



3 



DISEASES 



Sect. XIV. ^, 



2 



As walnut-leaves may be had In great quantity In the autumn and 

 the whole plant of fenecio jacobtca, rag-wort, at any tune, both which 

 are probably deleterious to infedls, as they feem never to be injured 



pro- 



by them, thefe might be procured at fmall expence, and mio-ht 

 bably, when dried and burnt, produce a fmoke equally deflrudlive 

 to them. 



Fifthly. The mofl: ingenious manner of deflroying the aphis would 

 be efFeded by the propagation of its greatefl: enemy, the larva of the 

 aphidivorous fly ; of which I have given a print, and which is faid by 

 Reaumeur, Tom. III. Mem. 9. to depofit its eggs, where the aphis 

 abounds ; and that, as foon as the larvis are produced, they devour 

 hundreds around them with the neceffity of no other movements but 

 by turning to the right or left, arrefling the aphis and fucking its juices. 

 If thefe eggs could be colle6led and carefully preferved dn 

 winter, and properly difpofed on necSlarine and peach-trees in the early 



ring the 



fprin 





or protedled from injury in hot-houfes ; it is probable, that 



this plague of the aphis might be counteraded by the natural means 

 of devouring one infed by another; as the ferpent of Mofes devour- 

 ed thofe of the magicians. 



Mr. Horrocks of Derby {hewed me this larva of the aphidivorous 

 fly, which I faw devour two or three aphifes, and Mr. Swanwick of 

 this town at my requeft made an accurate drawing both of the larva 



and fly, which he kindly favoured me with, accompanied with the 



following note. 



" On Augufl: the 4th Mr. Horrocks obligingly fent me an aphidi- 

 vorous larva in a box on a leaf of a plum-tree, on which were a 

 ftumber of aphifes ; and I had almoft immediately the pleafure of fee- 

 ing it eat one. 



" The method of taking his prey is thus : he is like the floth in 

 his difpofition, for he does not ramble about, while he has food around 



- 



him. He only lifts up his head, and ftrikes it down again, extending 



diredions, as if he was blind, and repeating the above 



8 



tion. 



