24 REPORT ON INJURIOUS INSECTS FOR 1904. 



THE PLUM BARK BEETLE. 



Scolytus rugulosus, Ratze. 



Branches of plum trees were forwarded by a correspondent 

 at Harvington, near Evesham, very badly attacked by this 

 beetle. Similar branches were later received from near Evesham. 



I have examined numerous trees infested with this beetle, 

 and in every case I have been satisfied that the tree was a diseased 

 or sickly one. I personally know of no case yet where vigorous 

 healthy trees have been attacked. 



In Warwickshire and Worcestershire, I have seen it only on 

 Plum trees, but it is known to attack apple, pear, cherry, peach, 

 etc., in other parts of the country. 



LIFE-HISTORY. 



The beetles (Fig. VIII. 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 





3 



FIG. VIII. THE PLUM BARK BEETLE (Scolytus rugulosus). 



i. 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. 



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. VIII, 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. IX. 

 Early in July the beetles hatch out and bore their way through 

 the bark and escape. This generation then reproduces itself, 

 the larvae remaining in the tree through the winter. 



