ADDITIONAL DATA ON THE LOCUST BORER. 35 



FAVORABLE AND UNFAVORABLE CONDITIONS FOli DESTRUCTIVE WORK. 



Favorable conditions for the destructive worlt of the borer appear 

 to be found in the presence of isolated trees and groves in the open in 

 localities where golden-rod is present or abundant; also, where less 

 resistant varieties of the tree prevail. 



Unfavorable conditions are found in forest growth or large areas of 

 pure stands, or mixed stands where the locust predominates; also, in 

 plantations and groves where resistant varieties prevail, and where 

 there is no golden-rod or other favorite food for the beetles. It is 

 also found that coarse, thick bark is less favorable than the thinner 

 bark on old and young trees and saplings. 



NATUBAIi ENEMIES. 

 INSECTS. 



Sevei-al predaceous insect enemies of the larvte have been observed, 

 but so far no true parasites have been discovered. A large elaterid 

 larva [Heiiiirhipus fa-^cicularis Fab.) appears to be the principal 

 enemy of the borer after the latter has entered the wood. It resembles 

 the borer somewhat, but is easily distinguished by the more flattened 

 and shiny body, long prothoracic legs and two curved spines on the 

 last abdominal segment. This predaceous larva is frequently f ouijd 

 in the empty mines of the Cyllene larvse, therefore it is evidently an 

 enemy of considerable importance. 



A slender, cylindrical, whitish, footless dipterous larva of an unde- 

 termined species is sometimes found in the mines in the wood, and, 

 according to an observation made by INIr. Pergande, it may attack and 

 kill the borere. 



Whitish, flattened larvse of the nitidulid genus Ips, with prominent 

 branched hooks on the last abdominal segment, are common in the sap 

 at the entrance of the mines and in the burrows made by the young 

 borers in the inner bark and outer wood. They are supposed to be 

 sap feeders, but the writer found they would attack and devour young 

 Cyllene larvae when confined together in a bottle. Therefore it is pos- 

 sible that they kill a great many of the young borers before these 

 Qnter the wood, which may account, in part, for the disappearance of 

 such a large number of the young borers while in the bark-boring 

 stage. 



It was also demonstrated that if several young Cyllene larvse of 

 various sizes were placed together in a small vial, the larger ones would 

 kill and eat the smaller ones. It is probable, therefore, that when 

 several larvse hatch from a cluster of eggs and but one survives — which 

 is usually the case — the larger or stronger one has killed the weaker 

 ones. 



