AODITTONAL DATA ON THK Ln(M'ST H<>HKK. 35 



KAVOKAHLK AND UNFAVOKABLE CONDITIONS FOU DKSTKl (TIVK WORK. 



Favomhlc coiulitions for thiMlostructivo work of the boror appear 

 to be found in the presence of isolated trees and j^roves in the open in 

 localities where ^'olden-rod is present or abundant; also, where less 

 resistant varieties of tlie tree prevail. 



Unfavorable conditioiis are found in forest <i;ro\vth or lar<,a' areas of 

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

 plantations and o-ro\es where resistant varieties prexail, and where 

 there is no ooJden-rod or othei" favorite food for the beetles. It is 

 also found that coarse, thick l)ark is, less favorable than the thinner 

 bark on old and youiii:" ti'ccs and saplings. 



NATURAL J:NEMIES. 

 INSECTS. 



Several predaceous insect enemies of the larva' have l)een observed, 

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

 larva {Ihmirhijnix fasclrnlari.^ Fab.) appears to l)e the principal 

 enemy of the l)oivr after the latter has entered the wood. It resembles 

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

 and shiny Ixnly. 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 larviv, therefore it is evidently an 

 enemy of considerable impoi'tance. 



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 Mr. IVigandc it may attack and 

 kill the t)orci-s. 



W liitish, flattened larva* of the nitidulid genus Ips. with ])roniinent 

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

 at the entrance of the mines and in the t)uri-ows ma(l«> by the young 

 borers in th<' innci- bark and outer wood. They are supposed to be 

 saj) f«'e(lers, but the writei- found they would attack and devour young 

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

 sil)le that tlwy kill a great many of the young boi-ers before these 

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

 such a large iuunl)er of the young borers while in the bark-)>oring 

 stag«\ 



It was also demonstrated that if several young Cyllene lar\;e of 

 vai'ious sizes were placed together in a small vial, the larger ones would 

 kill and eat the smaller ones. It is ])robable, therefore, that when 

 several larva* hatch from aclust«'rof eggs and but one survivcvs which 

 is usually the ca.se — the larger or stronger one has killed the weaker 

 ones. 



