BARK-BEETLES; ENGRAVER-BEETLES. 229 



up by the survivors. Both male and female of Xylcborus xylo- 

 graphus Say are shown in Fig. 242. 



A number of very minute beetles, belonging to the genera 

 Hypothenemus, and Pityophthorus, mine under the bark of the 

 apple, walnut, hickory, chestnut, and others. None are very de- 

 structive, however, as they are usually found in dead or dying 

 twigs, and none of them have such interesting habits as the am- 

 brosia-beetles, since their food consists of wood and not of fun- 

 gus grown by the mothers. 



THE FRUIT BARK-BEETLE. 



(Scoyltus rugulosus Ratz.). 



This beetle, not yet found in Minnesota, but uncomfortably 

 near it, needs a description, so that fruit-growers may recognize 

 this pest in time to combat it successfully. Prof. Smith gives a 

 full account of it in his text-book already mentioned, which is 

 here quoted : 



"Scolytus rugulosus, the 'fruit-bark beetle,' is, perhaps, the 

 best known, and certainly the most important economically, at- 

 tacking deciduous forest trees of almost all kinds. The black 

 parent beetles appear in early spring, and bore little round holes 

 through the bark to the sap-wood. They then make a central 

 burrow, on each side of which little notches are made to receive 

 the soft white eggs. The larva; hatch very soon, and at once be- 

 gin to make little burrows of their own, diverging as they move 

 from the parent channel, and gradually enlarging them as they 

 increase in size. When full grown they form a slightly enlarged 

 chamber, in which they pupate, and when they transform to little 

 beetles make their way out through little round holes in the bark. 

 The whole period of development does not exceed a month, and 

 there may be several broods during' the summer from the same 

 tree, the numerous galleries eventually girdling and killing it. 



"These insects rarely attack sound and healthy trees, and this 

 is a peculiarity of bark-beetles in general, though there are many 

 -exceptions. But just as soon as a tree becomes a little weakened 



