1910.] The Pear Leaf Blister Mite. 



123 



a high level of ' condition, and therefore of waste in his soil, 

 because he can get good prices for potatoes or barley or 

 sheep, whatever his staple product may be. But on poorer 

 land and with less suitable markets a man may be driven to 

 cut down his cake bill and spend only 10s. per acre on 

 fertilisers, because his products are not valuable enough to> 

 compensate for the waste at the higher level of condition in 

 the land. Thus the problem of what is a profitable manure 

 for a given crop becomes a very complex one, and the biggest 

 factor is perhaps the level of production at which the 

 individual farmer can conduct his business remuneratively. 



THE PEAR LEAF BLISTER MITE (Eriophyes pyri r 



Nalepa). 



The Pear Leaf Blister Mite (Eriophyes pyri, Nalepa) is a 

 troublesome enemy of the pear tree, and seems to be on the 

 increase. During 1908 and 1909, from May to September 

 inclusive, specimens of the mites or galled leaves were sent 

 to the Board from Sussex, Wilts, Devon, Somerset, Hereford, 

 Shropshire, Norfolk, and Yorkshire. Theobald and Collinge 

 in addition record cases in Bedford, Cambridge, Cheshire, 

 Cornwall, Lincoln, Northampton, Surrey, Warwick, Wor- 

 cester, and also from Wales. It is probably distributed over 

 the whole of England, but it does not appear as an epidemic- 

 Trees often remain unattacked in a garden, though in close 

 proximity to badly infested trees. 



Trees Attacked. — The Pear Leaf Blister Mite is an example 

 of a species of Eriophyes which feeds on plants of different 

 genera of the same Natural Order. According to Nalepa's 

 list, it infests not only the pear, but also the following other 

 British Rosaceous plants : Apple, White Beam Tree (Pyrus: 

 aria), Wild Service Tree (Pyrus torminalis), Rowan (Pyrus 

 aucuparia), and the rare Cotoneaster vulgaris, but the Board's- 

 records refer to pear trees only. 



The apple is very commonly attacked in America, as well 



as the pear. In Britain complaints relate chiefly to the 



destruction of the foliage of the pear, with the consequent 



effect on the fruit. Mite-infested pear leaves show character- 



j istic raised patches or blisters (Fig. 2) with a minute opening 



on the under side. The raised patches or blisters are red, or 



i green-red, or green, and later brown or brown-black. 



K 2 



