40 



INSECTS INJURIOUS TO THE APPLE. 



FIG. 28. 



No, 16. The Oyster-shell Bark-louse. 



Mytilaspis pomorum Bouch6. 



This is a very destructive and pernicious insect, which pre- 

 vails throughout the Northern United States and Canada, and 

 in some of the Southern States also. It was introduced from 

 Europe more than eighty years ago. It appears 

 in the form of minute scales, about one-sixth of 

 an inch long, of a brownish or grayish color, 

 closely resembling that of the bark of the tree, 

 and somewhat like the shell of an oyster in shape, 

 adhering to the surface of the bark, as shown in 

 Fig. 28, and placed irregularly, most of them 

 lengthwise of the limb or twig, with the smaller 

 end upwards. In some instances the branches of 

 apple-trees may be found literally covered and 

 crowded with these scales; and where thus so 

 prevalent they seriously impair the health and 

 vigor of the tree, and sometimes cause its death. 

 Under each of these scales will be found a 

 mass of eggs varying in number from fifteen or 

 twenty to one hundred or more; these during the 

 winter or early spring will be found to be white in color, but 

 before hatching they change to a yellowish hue, soon after 

 which the young insects appear. This usually occurs late in 

 May or early in June, and, if the weather is cool, the young 

 lice will remain several days under the scales before dis- 

 persing over the tree. As it becomes warmer, they leave their 

 shelter, and may be seen running all over the twigs looking 

 for suitable locations to which to attach themselves. They 

 then, under a magnifying-glass, present the appearance shown 

 at 2, Fig. 29, their actual length being only about one- 

 hundredth of an inch ; to the unaided eye they appear as 

 mere specks. A large proportion of them soon become fixed 

 around the base of the side-shoots of the terminal twigs, where, 

 inserting their tiny sharp beaks, they subsist upon the sap of 



