ADDITIONAL DATA ON TIIK LOCUST BORER. 35 



FAVORABLP] AND UNFAN OKA15LK CONDITIONS FOR DESTIil ( TIVK WORK. 



Favorahlo conditions for the destnu-tivo work of the hoicr appear 

 to ))(> found in tho presence of isolated tr(>o.s and j^roves in the open in 

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

 resistant varieties of the tree prevail. 



Unfavorabl(» conditions are found in forest growth oi' lari^e areas of 

 pure stands, or mixed stjinds 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 l»eetles. It is 

 also found that coarse, thick bark is less fiivoral)le than the thinner 

 hark on old and young trees and saplings. 



NATURAL ENEMIES. 

 INSECTS. 



Several predaceous insect enemies of the larva' have been o})served, 

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

 larva (Ileiui/'/u'pvs faxcicnlaris Fab.) appears to l)e the principal 

 enemy of the borer after the latter has entered th(^ 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 found 

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

 enemy of consideral)le 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 l>v Mr. Pergande. it may attack and 

 kill the borers. 



Whitish, flattened larvje 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 supposinl to be 

 saj) feeders, but the writer found they would attiick and devour 3'oung 

 Cyllene larva* when contined together in a bottle. Therefore it is pos- 

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

 enter the wood, which may account, in part, for th(^ disjippearance of 

 such a large number of the young l)orers whil(» in the bark-boring 

 stage. 



It was also dcmon.-^t rated that it' several yoiuig (JyiliMie larvte of 

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

 kill and eat the .smaller ones. It is probable, then^fore, that when 

 .seveial larvje 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. 



