174 FRUIT INSECTS 



emerges and seeks its mate. The yellowish females continue 

 to increase in size, remain grub-like in form and secrete the large, 

 brown portion of the scale, becoming full grown in August or 

 early September in the North. Egg-laying soon begins, the 

 body of the mother gradually shrinking into the smaller end of 

 the scale, and the 30 to 100 eggs occupying most of the space 

 beneath the scale. In New York, egg-laying sometimes begins 

 early in August, but in 1907 it was delayed until October in 

 some localities. There is but a single generation of the oyster- 

 shell scale in the North, but in southern New Jersey and Penn- 

 sylvania and farther south there are two generations annually. 



Fig. 172, — Old and recently set oyster-shell scales on willow. 



This oyster-shell scale has a wide range of food-plants. It 

 often nearly covers the bark of the larger branches (Fig. 170), 

 and even the twigs of apple and pear trees, and is often equally as 

 numerous on lilac bushes, willow, mountain ash and poplar 

 trees. It may also attack quince, plum, raspberry, currant and 

 fig among the fruits, and includes more than twenty-five shade 

 trees and shrubs in its list of host-plants. It infests trees of all 

 sizes and ages, often killing young trees and severely injuring 

 large ones. Orchards that are kept in a thrifty growing condition 

 and the trees not crowded rarely suffer serious injury from this 

 scale, but we have seen the lower limbs especially, and sometimes 

 the whole of large trees, killed by the insect where the trees were 

 crowded and neglected. Usually the bark of the tree only is 



