24 SECOND REPORT ON ECONOMIC BIOLOGY. 



THE PLUM BARK BEETLE. 



Scolytus rugulosus, Ratze. 



From various parts of the Midlands, branches of plum trees 

 infected with this beetle have been received. 



It is now generally agreed that this beetle only attacks sickly or 

 diseased trees. In addition to the plum trees, it is known to attack 

 apple, pear, cherry, peach, etc. 



2 



3 



FIG. 4. THE PLUM BARK BEETLE (Scolytus rngulosus). 



1. Beetle magnified, line showing natural length. 2. Larva,, natural size, and 

 much magnified. 3. Piece of apple branch, showing holes in bark made by 

 the beetle, and channels made in the wood. 



LIFE-HISTORY. 



The beetles (Fig. 4, i) make their appearance towards the end of 

 April, or early in May, and the female commences to bore holes in the 

 bark of the tree and so forms what are known as " mother galleries," 

 upon the sides of which she deposits her eggs. The larvae hatch out 

 in a few days, they are whitish, legless grubs scarcely one-tenth of an 

 inch in length, and lie in a curved position (Fig. 4, 2). The head is 

 yellowish or cream coloured. These now commence to feed on the 

 inner bark of the tree, forming " larval galleries " at almost right 

 angles to the " mother galleries." At the end of these secondary 

 channels small cavities are formed in which pupation takes place. 

 It sometimes happens that the larvae eat their way into the solid wood, 

 as shown in Fig. 4, 3. Early in July the beetles hatch out and bore 



