53 



t-lie case of an infested plum tree it will usually be noticed 

 that some of the twigs or smaller branches -are dead and that 

 numerous holes about the size of a No. 8 shot have been 

 bored through the bark which peels off disclosing little 

 tunnels that have Been made between the bark and the wood 

 (Fig. 6). Further search will probably reveal twigs not yet 

 dead and with a few holes only. On peeling the bark off 

 such a twig fresh borings containing beetles or grubs according 

 to the season will be found. Twigs damaged in this way 

 usually die and the infestation, if it becomes serious, no 

 longer remains confined to the twigs but extends to the larger 

 branches and even to the trunk itself, channels being driven 

 between the wood and the bark, or in the latter only if very 

 thick. The entire tree may thus be killed. The nature of the 

 attack on apple and the other trees is substantially the same 

 as that on plum, though it more seldom assumes serious 

 proportions. 



Description and Life-History. The adult beetles are 

 brownish-black insects of the form shown in the illustration 

 (Fig. 5b). In size they vary considerably but are usually 

 about one-sixteenth of an inch' in length. During warm 

 weather in spring the beetles leave their burrows, flying away 

 in search of fresh trees to attack. On discovering a suitable 

 tree the female selects a twig or branch and bores a hole 

 vertically through the bark. It then turns and bites out a 

 tunnel or brood chamber ^-% in. in length along the branch 

 between the bark and wood, laying eggs on each side as it goes. 

 From the egg a small white legless grub is hatched (Fig. 5a, 

 much enlarged), which at once begins to burrow a channel of 

 its own, passing first at right-angles to the brood chamber and 

 then, when clear of the latter, turning to right or left up or 

 down the branch. The grub feeds on the inner bark jusfc 

 next to the sap wood and goes burrowing on until full-grown 

 when it bites a small chamber, usually just in the sap wood, 

 and changes to a pupa. After spending a period as a pupa, 

 it turns to an adult beetle and bores its way out through the 

 bark to the outside fc each beetle making its own flight hole. 

 The presence of many holes therefore shows that a brood has 

 already hatched out. Fig. 6 shows a piece of a small plum 

 branch of which most of the bark has been peeled away. 

 The very black tunnels are the brood chambers from which 

 smaller channels pass to right and left getting gradually larger 

 and ending at a hole underneath which is the pupal chamber 

 and through which the adult beetles reached the outside of 

 the branch. It is difficult to say how many generations there 

 are in the year, but there are probably two main broods, 

 the first appearing in spring and the second in summer. The 

 descendants (larvae) of the second brood may in hot summers 

 feed up rapidly and give rise to yet a third generation of adult 



