148 INJURIOUS IKSECTS 



material damage, for the reason, doubtless, that there 

 have, hitherto, always been natural enemies and parasites 

 enough to keep it in due bounds. 



THE OYSTER-SHELL BAEK-LOUSE. 

 (Mytilaspis pomicorticis, Riley.) 



The Oyster-shell Bark-louse, was formerly known as 

 Aspidiotus conchiformis, but changed by Prof. Eiley for 

 good reasons to the name given above. It is one of the 

 most pernicious and destructive insects with which the 



apple-grower in the North- 

 ern States has to contend. 

 This species presents the 

 appearance of figure 99, 

 and may always be dis- 

 Fig. 99.-OTSTEK-SHELL BABK^" tinguished from the pre- 



ceding, by having a very 

 uniform mussel-shaped scale of an ash-gray color (the 

 identical color of the bark), and by these scales, contain- 

 ing, in the winter time, not red, but pure white eggs. 



There is scarcely an apple-orchard in Northern Illinois, 

 in Iowa, or in Wisconsin, that has not suffered more or 

 less from its attacks, and many an one has been slowly 

 but surely bled to death by this tiny sap-sucker. It was 

 introduced into the Eastern States about the beginning 

 of the present century, from Europe, and had already 

 reached as far west as Wisconsin in 1840, from whence it 

 spread at a most alarming rate throughout the districts 

 bordering on Lake Michigan. It occurs at the present 

 time in Minnesota and Iowa, but whether or not it 

 extends westward beyond the Missouri River, there are 

 no data to show. Its extension southward is undoubtedly 

 limited, for though so abundant in the northern half of 



