THE PEACH-TREE BARKBEETLE. 95 



tree about 14 inches in diameter and from 75 to 80 feet high which 

 had apparently been killed by the beetles, the bark having been 

 completely eaten away from the tree. 



The adults or beetles (see fig. 20, «, b) produce the primary injury 

 to healthy trees, the work of the larva» being secondary. The healthy 

 trees, by repeated attacks of the adults, are reduced to a condition 

 favorable to the formation of egf^ burrows. "S^Hien the beetles are 

 ready to hibernate in the fall they fiy to the healthy trees and form 

 their hibernation cells. These latter are injurious to the trees, for 

 through each cell there will be a tiny flow of sap during the following 

 season. (See PI. XI, fig. 2.) 



The greater the number of hibernation cells, the greater will be the 

 amount of sap exuded ; also, Avhen the beetles come out of their winter 

 quarters in the spring they bore into the bark of healthy trees from 

 one-quarter to one-half of an inch, either for food or in an endeavor 

 to form egg burrows. Later the beetles leave these burrows, either 

 because the burrows become filled with sap or because the beetles seek 

 the sickly trees for breeding purposes. Many more small channels 

 are thus formed in the bark and from these sap oozes during the 

 summer. Two means are therefore supplied by which the sap may 

 flow from the trees — and this it does in many cases, forming large 

 gummy masses around the trunks. Such losses for three or four years 

 in succession necessarily reduce the trees to a very much w'eakened 

 condition, and it then becomes possible for the beetles to form egg 

 burrows and for the larva' to finish the destruction of the tree. Plate 

 XI, figure 3, shows the remains of an orchard presumably killed by 

 PhloiotrihuH liminaii's. 



LIFE HISTORY. 



HIBERNATION. 



The insects spend the winter as adults in hibernation cells just be- 

 neath the outer layer of bark on both healthy and unhealthy trees. 

 In the fall, from October to freezing weather, the adults of the fall 

 generation are continually emerging and migrating to growing trees. 

 They bore in through rough places on the bark and burrow along 

 from one-quarter to five-eighths of an inch, forming hibernation cells, 

 the openings to which are closed with the exudation from the bur- 

 row. In these cells they reuuiin throughout the winter. The latest 

 formed adults of the fall brood remain in the pupal cells until spring 

 before cutting out, so that hibernation occurs both on dead and living 

 trees, those on the live trees hibernating in regular hibernating cells 

 and those on dead trees hibernating in the pupal cells. 

 66824— Bull. 68, pt 9—09 2 



