MONTANA EXPERIMENT STATION. 



159 



that from this fact tlic apple twig-borer is another pest that is par- 

 ticularly liable to be transferred on nursery stock. The eggs are 

 laid in the early spring months, the beetles leaving their hibernating 

 quarters for this purpose. The larva bores through the center of 

 the twig until fall when it pupates later transforming to a beetle and 

 going into hibernation as above described. There is but one brood. 

 The adult of the insect which is the form liable to appear on nur- 

 sery stock is about % inch in length, cylindrical in general shape and 

 brown in color. 



THE FRUIT-TREE BARK-BEETLE. 



The fruit-tree bark-beetle is an introduced insect that attacks the 

 bark of plum, peach, cherry, and apple trees. The bark may be 

 thickly peppered with fine holes as though by fine bird shot. See 

 figure 9. These are the entrance and exit holes of the small beetle 

 illustrated, greatly enlarged at Figure 8 a and b. The grubs ex- 

 cavate narrow galleries in various directions under the bark often 

 killii).; a tree or part of its branches. The beetle usually attacks 

 only sickly or unthrifty trees. 



The adult beetles appear in the spring and begin burrowing 

 through the bark. Upon reaching the sap wood, feeding as she 

 goes, the female constructs, partly in the bark and partly in the wood 

 next to it, a vertical gallery or "brood chamber", and along the 

 sides of this at short intervals she gnaws little pockets in each one 

 of which she deposits an egg. The very minute, whitish, grub-like 

 larvae that hatch from these eggs excavate galleries that start out 

 at right angles to the brood chamber. These side galleries soon 



Fig. 8. The Fruit-tree Bark-beetle: a, adult beetle; b, same in profile; c, 

 pupa; d, larva — all magnified about ten times. (Chittenden, Circular 29, Sec. 

 Series, t^'v. of Entomology, U. S. Dept. or Agr.) 



