54 



beetles, but most of them p rob ably feed more slowly spending 

 the winter in the twigs and producing the first brood of the 

 following year. 



Other Species of Bark Beetle. A slightly larger kind of 

 Bark Beetle (Scolytus pruni, Eatz.), though rare, is occasion- 

 ally found in old apple and pear plantations, working in much 

 the same manner as the one above ($. rugulosus), though 

 preferring the larger branches and trunk. It seldom seems 

 sufficiently numerous to be injurious. A further kind of Bark 

 Beetle (Scolytus destructor, Oliv.) is found on elms, to which 

 it may be most harmful. It is only mentioned here as the 

 question is sometimes asked as to whether infested elms are 

 a danger to fruit 'trees. So far as is known this is not the 

 case as the Elm Bark Beetle does not live in any kind of 

 fruit tree. 



II. SHOT BORER BEETLES. 

 (Xyleborus di&par, Fab and X. saxeseni, Eatz.) 



Trees Attacked and Nature of Damage. Both species of 

 Shot Borer attack a great variety of trees including plum, 

 apple, pear, oak, sycamore, chestnut and (abroad) conifers, 

 but in this country the plum appears to suffer most injury. 

 In contrast to the Bark Beetles, Shot Borers work in the hard 

 wood, leaving the bark untouched except for an occasional 

 small circular hole showing where the beetles first entered. 

 In further contrast to the Bark Beetles is the remarkable fact 

 that both Shot Borers and their grubs feed primarily, not on 

 the wood itself but on a form of fungus which grows on the 

 walls of their tunnels (possibly also on the sap which oozes 

 into them). As the colonies of beetles are large in number 

 they naturally require extensive burrows and the damage is 

 correspondingly great, the wood being so tunnelled as to 

 weaken or even kill the tree. 



The two species of Shot Borer may. be known. by the shape 

 of their borings. The common Shot Borer (X. dispar) always 

 makes circular Burrows such as might have been drilled with 

 a tool. The first hole is bored in through the bark and from 

 I to \ in. into the wood. It then turns to right or left round 

 the branch following a growth ring and from this burrow still 

 more are made passing up or down the branch parallel with 

 its length. The holes throughout are circular and of approxi- 

 mately the diameter of the beetles themselves. Fig 4 shows 

 a section of a branch cutting through Both vertical and 

 horizontal channels. In the other species sometimes called 

 the Flat-Celled Shot Borer (X. saxeseni)--ihe .first tunnel 

 passing in through the bark into the wood is also round, but 

 once into the hard wood the burrows 'are extended up and down 

 so as to make large flat cavities or slits about one-sixteenth 

 of : an inch in depth and -1 in. in length and breadth. Fig. 2 



