PEAR LEAF-BLISTER MITES. 



8? 



The Pear-leaf disease known as " blister," caused by a very minute 

 Mite (figured at p. 86 enormously magnified), is an infestation which 

 does much harm in some places, and appears to be steadily increasing, 

 partly by reason of the damage noticeable on the Pear-leaves not 

 being so well understood as it ought to be, and partly because hitherto 

 in this country little has been known as to reliable measures, easily 

 carried out, for keeping the mischief in check. 



In the United States and Canada, however, the "leaf-blister" 

 disease increased of late years to such a serious extent that special 

 attention has been bestowed on the subject, and some very good 

 information on its life-history and practicable remedial measures were 

 given by Mr. J. Fletcher, Entomologist of the Dominion Experimental 

 Farms of Canada, for which see "Keport of the Ontario Fruit-growers' 

 Association," p. 113, published in the * Annual Eeport of the Depart- 

 ment of Agriculture of Ontario for 1892.' 



Experiments were also set on foot in 1892, and repeated (to 

 ensure correct observation) in 1893, at the Agricultural Experiment 

 Station, Cornell University, New York State, U.S.A., and the main 

 points regarding the treatment which proved very successful, and the 

 life-history of the pest, were embodied in a pamphlet of about ten 

 pages in length, by Mr. M. V. Slingerland (Assistant Entomologist, 

 Cornell University), which may be strongly recommended to all 

 needing information on the subject.''' 



In my Eeport for 1893, I gave as much of the minute technical 

 characteristics of this Pear Leaf-blister Mite as can be needed for 

 most practical observers, from the description by Dr. Alfred Nalepa in 

 the part mentioned below t of his long series of elaborate works on 

 the Gall Mites published in ' Reports of the Proceedings of the Imperial 

 Society of Vienna ' ; but for common use, the following short note of 

 the appearance of the diseased leaves, and of the Gall Mites, which 

 cause the blisters, may be of service. 



The disease shows itself in the form of blister-like spots, somewhat 

 raised on each side of the leaf, and in the middle of each little blister 

 beneath the leaf is a little hole, which gives access to the central 

 cavity, and also gives passage out at pleasure to the Mites. The spots 

 or blisters may be found on the Pear-leaves whilst they are still quite 

 young, but later on, when they are expanded, is the period at which 



• Bulletin 61, Dec, 1893. Cornell University Agricultural Experiment Station. 

 By Mark Vernon Slingerland. Published by the University, Ithaca, New York, 

 U.S.A. Procurable through Messrs. W. Wesley & Son, Essex Street, Strand, 

 London, W.C. 



t Nalepa, ' Zur System der Gallmilben,' Sitzsber. 1890, pp. [50, 51] 11, 12, 

 plate iv., figs. 1, 2. See also references in 'Katalog der bisher beschrieben Gall* 

 milben,' by Dr. Nalepa, pp. 275 and 296. 



