340 REPORT OF STATE BOARD OF HORTICULTURE. 



ITS FOOD HABITS. 



In this country the fruit-tree bark-beetle attacks various varieties of the 

 plum, cherry, apricot, nectarine, peach, apple, pear, and quince. In Europe 

 it not only infests the above fruit trees, but also works on the elm, mountain 

 ash and hawthorn. Although it has apparently never been recorded as 

 attacking these trees in the United States, nevertheless it may possibly do so 

 later. The stone fruits seem to be more especially subject to the attacks of 

 this beetle, the plum, perhaps, most of all ; but since our orchards are prin- 

 cipally peach and apple, it is with these trees that the greatest amount of 

 damage is done, if we consider the state at lai'ge. Fully three-fourths of 

 the complaints from this beetle have been from its work on these two fruits. 



From what we have observed during the past two years, it is evident that 

 the beetles prefer and will attack first of all those trees or parts of trees 

 that are injured, weakened, or dying from any cause whatever; still we have 

 seen many trees infested with this insect that were apparently as healthy 

 and sound as any tree, and for that reason it appears this insect is capable of 

 doing more damage than was at fii-st supposed. 



It is very largely a matter of opinion when one pronounces a tree perfectly 

 healthy that has become infested with this pest, but, no doubt, one should 

 regard a tree as healthy when there is absolutely no reason to suspect any- 

 thing different except that it has now become attacked by this insect. Those 

 who still entertain the oponion that this beetle will attack only devitalized 

 trees, would surely have trouble in detecting- all such cases of devitalization 

 in our orchards, were no fruit-tree bark-beetle' present to lead the way. 

 Looking at the subject from another point of view, it may be a question 

 whether any of our apple trees, for instance, are not devitalized that are 

 found in the southern half of this state, where it is practically impossible to 

 find them free from the wooly aphis. Nevertheless, it seems plausible to 

 regard the greater bulk of these trees as healthy. 



No doubt one of the greatest agencies at work to'assist in the multiplica- 

 tion of this beetle in Missouri is the wooly aphis, which has so devitalized 

 and killed such a large number of the apjale trees in southern orchards that 

 it has made the conditions most favorable to the development of this bark- 

 beetle in those trees. The greater number of peach trees that are attacked 

 by this bark-beetle owe such an attack to the fact that they are suffering in 

 our orchards from the work of the peach-tree borer, which is weakening 

 and killing many, and from the winds and overbearing, which are breaking 

 large limbs and forming the best of breeding places for this pest. It is sure 

 to attack such trees first. Trees that have just been transplanted, as in set- 

 ting out a young orchard, are also frequently attacked by these beetles, but 

 this may be largely due to the checked vigor resulting from such a change. 

 A perfectly healthy and vigorous tree will frequently repel the attack of the 

 fruit-tree bark-beetle by the copious flow and exudation of sap. This is 

 especially the case with the stone fruits, where the beetles appear to be 

 driven away by this means, and are unable to burrow to any considerable 

 dista.nce below the bark and are unable to deposit their eggs. 



When the bettles attack a comparatively small limb, perhaps the first 



