INSECTS INJURIOUS TO THE APPLE AND PEAR 



593 



It is probably our most common scale insect, being almost always 

 found on apple trees, on which it works on the bark or the twigs 

 and trunk, reproducing even on old trunks, where the scales will 

 be found under the loose bark and are undoubtedly a factor in 

 causing the bark to slough off. All of the common orchard trees 

 are occasionally infested but rarely injured, as are also maple, 

 poplar, horse-chestnut, willow and lilac. Quaintance and Sasscer 



FIG. 447. The oyster-shell scale (Lepidosaphes ulmi Linn.): a, female 

 scales on twig; b, female scales from above; c, same from below showing 

 eggs; d, male scale enlarged. (After Howard.) 



give a list of over 100 trees, shrubs, and plants upon which the 

 scales have been found. The species is a cosmopolitan one, 

 being introduced into this country at an early date and now 

 being found in every State, and occurs throughout the world where 

 the food-plants exist. 



The mature female scale is about one-eighth inch long, of a 

 dark-brown color, sometimes almost blackish, and shaped some 

 what like an oyster-shell, as shown in Fig. 447. The male scale is 



