55 



shows a section of a branch cut to show these cavities both' 

 from the side and from the top. Possibly on account of the' 

 size of these burrows, this species seems to prefer larger' 

 branches (or trunks) than the ordinary Shot Borer. 



In both species the walls of the burrows are stained by the 

 fungus black in the case of the ordinary Shot Borer, brown 

 or partly brown in the Flat-Celled Borer. In each case the 

 stains extend in the wood for some distance from the burrows 

 so that a branch cut off even at a point where it appears t<y 

 be sound may show a characteristic brown stain. 



Description and Life-History. (a) Shot Borer Beetle. 

 (Xyleborus dispar). The adult beetles are small black-brown.' 

 insects, the female (Fig. 3a) about J in. in length and the 

 male (Fig. 3b) much shorter. In spring the female bores 

 into the tree and lays eggs in the burrows. White legless 

 grubs are hatched from the eggs and feed on the fungus on 

 the walls of the borings, and also perhaps on the exuding sap. 

 On becoming full-fed these grubs turn to pupae and then tci 

 adult beetles, which may be found packed so tight in the 



talleries (just like shot) that it is incredible how each beetle 

 nds enough to feed upon. These beetles again carry on the 

 work of lengthening the burrows in which the winter is spent. 

 It seems uncertain whether there is more than one generation 

 in the year. On the Continent two have been recorded, but 

 in England there is possibly only one main brood. Males are 

 very rare in the burrows except in winter when they may 

 outnumber the females. Unless therefore the females can lay 

 eggs without pairing, most of them would be forced to wait 

 until late autumn or winter before breeding. 



(b) The life-history and appearance of the Flat-Celled 

 Borer (Xyleborus saxes eni)' is substantially the. same as that 

 of the Shot Borer but the beetles themselves (Fig. 1) ar^ 

 much smaller and there is not the marked difference in size 

 and shape between the sexes. Again there is some doubt as 

 to the number of generations in the year, but as a rule beetles 

 of both sexes and grubs of different ages may all be found 

 together in the large flat brood chambers, and there may 

 well Be two broods each year. 



III. METHODS OF CONTROL. 



In the case of both Bark and Shot Borer Beetles, control 

 measures are preventive rather than remedial, and the same 

 remarks apply more or less to all. 



1. There is no doubt that trees in an unhealthy state, either 

 because of the attacks of other pests or because of unsuitable 

 conditions, are preferred by the beetles, probably because they 

 are not hindered in their burrow-making By too free a flow 

 of sap. THus a Bad attack by Aphides or Brown Hot oh 

 plums, with the resulting weakening or death of twigs, is "very 

 likely to cause ah increased infestation by Bark Beetles. In 



