general rule do not thrive on the thin bar):. In the second, 

 group cone various engraver "beetles (Ips, Pityophthorus, 

 Eccoptogaster, etc.) killing pole and sapling stands and top 

 of trees. Many spi ho -topped and flat -topped trees are the 

 result of these attacks. 



Other insects kill trees besides tho various spe- 

 cies of beetles, such as sawflies, hornflies, scales, moths, 

 etc. These instances, however, are rare, occur locally and 

 must he treated separately, with an investigation of each 

 case as it becomes known, and is reported. Ord..inaril3r trees 

 of certain species are killed by one or tv.ro insect species, 

 depending on whether the tree is young or mature. ?hus ma- 

 ture yellow pines are general^ killed by the 'Je stern pine 

 3eetie (Dendroctonus brevicomis) and young growth by an Ips 

 ( Ips confusus), mature sugar pines "ay the Mountain Pine 

 Beetle (Dendroctonus monticolae), mature firs, both red and 

 white, by a round -head borer (Tetropiura ablet is), and young 

 firs by an engraver (Eccoptogaster subscaber). Mature Jef- 

 frey pines are killed by the Jeffrey Pine Beetle (Dendroc- 

 tonus jeffreyi), or, in the extreme southern Sierras, by a 

 flat -head (Helanophila gentilis). Douglas firs, if mature, 

 are killed by the Douglas F'ir Beetle (Dendroctonus pseud, ot- 

 sugae), and young Douglas firs by a certain engraver (He cop - 

 togaster unispinosus ) . 



h 



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