36 



GENERAL ZOOLOGY 



They settle down at once and form permanent shelters over 

 their backs. Although the male, after hatching, at first 

 resembles the female, it emerges (Fig. 20) from its scale 

 after a time as a free-living, two-winged insect. 



The San Jose* scale 

 (Aspidio'tus perni- 

 cio'sus, Fig. 21) was 

 introduced from the 

 Orient into this coun- 

 try about 1886. Since 

 that time it has spread 

 over the entire United 

 States and is one of 

 the most serious men- 

 aces to orchards. Tens 

 of thousands of acres 

 of fruit trees have 

 been killed outright 

 by this scale alone. 



Oyster-shell scale 

 (Lepidosa'phes ul'mi) 

 attacks many shrubs 

 and fruit and shade 

 trees. It reproduces 

 so rapidly that the 

 entire bark becomes 

 incrusted with the scales (Fig. 22, c), and the trees soon 

 die unless the scales are killed or removed. 



There are hundreds of species of scale insects some of 

 which are limited to a single food plant, although others 

 flourish on a great variety. The cottony scales are especially 

 destructive of shade trees. Oranges and other citrus fruits 

 are attacked by several species, the scales of which are 

 frequently observable on the skins of the marketed fruits. 



Fig. 21. San Jose scale on young twig 



Photograph by the Illinois State Natural 

 History Survey 



