Mr. R. H. Lewis on Apple Blight. 21 



IV. Explanation of the sudden appearance of the fVeh- 

 spinning Blight of the Apple, Hawthoi'n, Sfc. By R. H, 

 Lewis, Ksq., 3I.E.S. 



[Read January 6, 1834.] 



There is, perhajis, no " blight" which, in its later stages, has at- 

 tracted more attention, or the devastation caused by which is so 

 well known, as that which infests the apple, whitethorn, and various 

 other trees ; yet, as far as I have been able to ascertain, its early 

 history has hitherto been veiled in obscurity. The oeconomy of the 

 species of insect to which it is attributable was fully investigated 

 during the last season by my brother, E. W. Lewis ; but his death 

 and my not being able to find his notes, prevent that minute detail 

 which would otherwise have been given. The following observations 

 have been drawTi up from some notes which I made at the time. 



The mother moth (Yponomeuta padella, Linn.,) deposits her eggs 

 in the preceding year, generally on the small twigs, and chiefly on 

 their under surface, in a circular patch about 1^ line in diameter, 

 which she covers over with a strong gluten, at first of a pale yellow, 

 but which is afterwards, by the action of the atmosphere and rain, 

 changed to a dark brown, very closely resembling the bark of the 

 tree, and is then very difficult to be distinguished from it. 



The eggs hatch early in the autumn*, and the larv'se remain in 

 confinement during the whole winter, under the covering which is 

 formed by the gluten and egg-shells. If we now raise up one of 

 these excrescences we shall find it hollow inside, and containing two 

 dozen or more larvae, of a pale yellow colour, with the head and a 

 corneous plate on the first segment black, and about half or two 

 thirds of a line long. In these receptacles they increase somewhat in 

 size ; the bark of the tree beneath is moist and green, but whether, 

 or in what manner, they derive nourishment from it I am at a loss 

 to say. 



About the time that the trees are coming into leaf they make their 

 escape ; but they do not now commence spinning webs, — they can- 

 not yet eat the epidermis of the leaves, and they require some pro- 

 tection from the cold and rain, which their tender frames are not 

 yet fitted to endure ; to effect which they mine into the leaves, eating 

 the parenchyma only, and leaving the epidermis untouched. 



* The exact time I did not ascertain : I found them hatched the beginning 

 of October. 



