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REPORT ON INJURIOUS INSECTS FOR 1904. 



It is a common species, occurring all over the world, and 

 exceedingly destructive.. It is known under a variety of popular 

 names, such as the apple tree bark louse, oyster shell bark louse, 

 oyster scale, mussel scale, etc. 



The adult female scale is about one-eighth ofjanjinch in 

 length, usually it exhibits a slight curve and widens from before 

 backwards. At the anterior or pointed end is a small yellowish 

 pellicle with a scale attached, in addition there is a larger 

 pellicle to which is attached the remainder of the brownish or 

 greyish-brown scale, marked with numerous fine transverse 

 curved lines. Beneath this covering scale is the female insect, 

 which occupies the anterior portion (Fig. VI, i 3). 



The male scale is much smaller than the female scale. 



LIFE-HISTORY. 



The life-cycle is completed jn a year, though in some coun- 

 tries two generations are produced each year. During August 

 the female deposits from fifty to one hundred oval, whitish eggs, 



i 3 2 



FIG. VI. THE MUSSEL SCALE (Mytilaspis pomorum). 



i. Upper surface of female scale. 2. Lower surface of same. 3. Eggs. 

 All greatly enlarged. 



which remain beneath the protecting scale during the winter, 

 hatching out from May to early June into small, active, six- 

 legged larvae, which now proceed to creep from beneath the 

 parent scale. These soon settle down and commence sucking 

 nourishment from the underlying tissues. After about two days, 

 long, white, waxy filaments may be seen forming on the back of 

 each, and this, after a time, with the cast skin of the young, 

 becomes the scale-like covering. A second moult then occurs, 

 and to the cast skin a still larger scale becomes attached. During 

 this period the larvae have lost their six legs, and now take the 

 form of small, yellowish, fleshy grubs. In the case of the females 

 they remain beneath the scales, and after depositing their eggs, 

 die. Reproduction in most cases is asexual. 



