370 



EFFECTS PRODUCED BY SUCKING INSECTS AND 

 RED SPIDER UPON POTATO FOLIAGE. 



By a. S. HORNE and H. M. LEFROY. 



{Royal Horticultural Society's Gardens, Wisley.) 



(Plates XXIII- XXVII.) 



A SERIES of experiments is here described which was designed to 

 ascertain accurately what effects are produced in potato foliage by the 

 action of sucking insects. 



The potato plants used were seedlings of the President variety, a 

 variety particularly subject to the curl disease. The first seedlings 

 were raised at Chelsea in 1911 and subsequent series of plants at 

 Chelsea, Wisley and at Messrs Sutton's trial grounds. The greater 

 number were raised at Wisley, 1912-1914, nearly a thousand plants 

 in all. 



The raising of these plants from seed, their variability and behaviour 

 under different conditions of growth, and experiments with them 

 not directly concerned with this present work will be described else- 

 where. 



The objects we hoped to attain and succeeded in attaining were 

 firstly, to be in a position to assign definite symptoms to certain insects 

 and so to be able to eliminate them at once if one is seeking effects 

 produced by fungi or bacteria, as, for example, in the curl disease where 

 pathological symptoms such as dwarfing, yellowness, blotching and 

 dead leaf ends occur; and, secondly, the application of this knowledge 

 in seeking the distribution of pathological conditions due to insects in 

 the field. 



A result of this work was the investigation of the mechanism of 

 sucking in two of the species concerned, in Lygus by P. R. Awati {Proc. 

 Zool. Soc. September 1914) and in Aleurodes by E. Hargreaves {Ann, 

 App. Biol. I. Nos. .'5 and 4). 



