The Mussel Scale. 
75 
The Mussel Scale or Oyster-Shell Back Louse. 
( Mytilaspis pomorum, Bouclie.) 
Numerous enquiries are constantly being made by fruit-growers 
and gardeners concerning the Mussel Scale (. Mytilaspis pomorum). 
There being no leaflets issued or other ready information for fruit- 
growers, the following notes have been prepared with a view to 
meeting this want. 
The Mussel Scale is found chiefly on apple, but also on pear, 
currant, plum and wild Crataegus, such as the Hawthorn. I have 
also found it abundantly on Blackthorn in Devonshire. This 
Fig 8. — mussel scale (Mytilaspis pomorum). 
a, Upper ; b, lower surface of 9 scale ; c, cf scale. (Greatly enlarged.) 
pest, the worst scale insect we have in Great Britain, is found in 
North America, and also in Australia, New Zealand, and South 
Africa, having been imported on nursery stock. In this latter way 
it is also largely distributed in this country. The necessity of 
fumigating young stock before planting is thus rendered essential 
and should be done by all nurserymen before their stock is sent out. 
A few scales may easily escape detection and so set up a large 
colony, to the detriment and even death of the tree. I know of no 
district in England where this pest does not occur in greater or less 
abundance. Old trees and neglected orchards chiefly encourage it, 
but young stock suffer far more than old. 
This scale insect is frequently taken for growths on the bark. 
The scale is the product of a minute insect belonging to the 
