CHAPTER XX 

 INSECTS 



MUSSEL SCALE (Reports, VI, 6; VIII, 33) 



THE common mussel scale (Lepidosaphes ulmi) is one of the best 

 known coccid pests, attacking the pear, hawthorn and other 

 plants, besides the apple. It owes its common name to the 

 resemblance of the scale to a minute mussel shell, but another 

 name is also given to it in America and Canada (and also by our 

 Board of Agriculture), namely, that of the " Oyster-shell bark 

 louse," although it bears no resemblance to an oyster-shell, and 

 although, also, that name has already been applied appropriately 

 to another scale Aspidiotus ostrea/ormis met with only under 

 glass in this country. 1 



The mussel scale may be found thickly studded over the bark 

 of apple trees (Fig. 20), especially on those parts of the tree 

 where growth is not very active, as the trunk, main branches and- 

 fruit spurs. It may easily be removed with the finger nail, 

 and, when examined under the microscope, will be seen to con- 

 sist of a shell covering a large number often 40 or 50 of white 

 eggs (Fig. 21). The insect itself is much smaller than the scale 

 which it manufactures, and occupies only the apex of this latter ; 

 but, as it dies in September, nothing can be seen during the 

 winter but the remains of its shrivelled body, and the eggs 

 which it has laid. At the end of May or the beginning of June 

 (or up to the end of June, according to Canadian authorities), 

 the eggs hatch out, giving rise to active white larvae ; these soon 

 fix themselves to the bark, from which they suck the sap, and 

 begin covering themselves with scale. The male insect is winged, 

 and is exceedingly rare ; it forms a much smaller scale than the 

 female insect. 



These insects have enemies : ladybirds and their larvae eat 

 them, and the larvae of a species of chalcididce (Aphelinus myti- 

 laspidis) are often found in large numbers under the scales, 

 feeding on the eggs. These, however, are much localised, and even 



1 See Newstead, Journ. Rov. Hort. Soc., 1900, 236. 

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