EXPERIMENT STATION BULLETINS. 



141 



therefore containing less sap, seem like unhealthy wood to the l)cetles, which prefer 

 them to the more vigorous trees. The poles should be set during the last part of 

 May and removed and burned some time in July, after making a careful examina- 

 tion to see if the young grubs are present. This method has been successfully em- 

 ployed in Germany in the case of another beetle having somewhat similar habits, and 

 will prove useful in cases where the affected trees are valuable. Although these 

 methods will not altogether exterminate the beetles, they should greatly reduce their 

 numbers, so that the harm done will be comparatively slight. 



While these insects prefer unhealthy wood to that which is healthy, they do not 

 seem to know just where to draw the line, and their tunneling will sometimes cause 

 the loss of an entire limb or even an entire tree, when but for them the loss might have 

 been confined to one or two comparatively small branches. It is quite likely that they 

 do occasionally attack healthy wood : at least it is thought that they greatly hasten 

 the decay of healthy trees. 



17. THE FRUIT BARK-BEETLE. 



(Scolytus rugulosus.) 



In 1878, Dr. LeConte noticed a small beetle working in the bark of fruit trees in 

 this country." Since that time the beetle has gradually spread over a considerable 

 portion of the United States. Its first appearance in Michigan was in the season of 

 1897, but as only a single specimen of the work was obtained, with none of the beetles 

 themselves, it was thought best to wait until more material was obtained before pulv 

 lishing an account of the pest, in order to guard against adding another care to the 

 many troubles of fruit-raisers without sufficient reason. 



The first intimation of the trouble is in the discovery of numbers of small drops of 

 gum exuding from punctures in the body or limbs of peach, plum, cherry or apple 

 trees. A closer examination reveals a small round hole a little less than one-sixteenth 

 of an inch in diameter under each droj) of gum. If now the outer bark around the 

 hole be removed or pared away, a small burrow will be found to extend for a longer 

 or shorter distance in the layer between the wood and the bark, sometimes branching 

 considerably. These burrows or galleries usually exhibit a regular and definite ar- 

 rangement (Fig. 18) when carefully examined: there is an egg or brood-chamber, short 



Kig. 18. Wood eaten by licolij/us i-ki/k/osks. (Original.) 



and roomy, and from the sides of this chamber extend, in a direetion more or less 

 transverse to it, many slender galleries, small and narrow at the center, but gradually 



* Am. Phil. Soc. (Proc.) Vol. XVII (1878;) p. 626. 



