INSECT ENEMIES OF WESTERN FORESTS 



151 



The ponderous borer {Ergates spiculatus Lee.) is very destruc- 

 tive to the wood of recently killed or felled coniferous trees, to 

 fallen logs and stumps, and even to power and telephone poles. Re- 

 cently it has been found to be a most important determining factor 

 in the salvage of fire-killed Douglas fir. The heartwood of this tree 

 is very resistant to deterioration until penetrated by the large mines 

 of this wood-boring species. The adults are the largest of our 

 western beetles, measuring from II/2 to 2i/4 inches in length (fig. 74). 



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Figure 74. — Larvae and adult of the ponderous borer (Ergates spiculatus). Natural size. 



The color is uniformly dark brown, with the head and thorax some- 

 what darker than the elytra. ' The sides of the prothorax are armed 

 with a few large or many .small teeth or spines. They are often 

 found flying around lights early in the summer. Eggs usually are 

 laid in crevices of the bark of dead trees or stumps, and the larvae 

 excavate large channels, packed with coarsely chewed wood fiber, 

 in the sapwood and then into the heartwood. When full grown the 

 large, thick-bodied larvae are often 21/2 inches in length, creamy 

 white, with reddish heads bearing plates armed with four spines just 

 above the mandibles. The species is found throughout the Western 

 States, commonly attacking Douglas fir and pines but also other 

 conifers. 



The California prionus {Prionus calif ornicus Mots.) is another 

 large species very similar to the foregoing. The larvae feed in the 

 w^ood of oak, alder, poplar, and other hardwoods, sometimes boring 

 into the roots of living trees. The adults usually have three promi- 

 nent spines on the lateral margins of the prothorax. The larvae are 

 very similar to those of Ergates. 



