138 



MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTUllE 



BARK WEEVILS 



Some bark weevils of the genus Pissodes (45) are particularly im- 

 portant as enemies of terminal shoots (p. 33) ; others attack the basal 

 portion of the trunk of small trees and ma}^ extend their work into the 

 roots. Weakened, suppressed, and decadent trees are usually preferred, 

 but under some conditions these insects may attack healthy trees' 



Usually they breed under 

 the bark of logs, in stumps, 

 or under the bark of dying, 

 standing trees and hence 

 of little 



are 



economic im- 



portance. 



The adults are stout bee- 

 tles with uniform or varie- 

 gated markings of yellow, 

 brown, or black. The head 

 is prolonged into a snout 

 or break, which is used to 

 puncture buds and tender 

 bark of terminal or lateral 

 branches for feeding pur- 

 poses, and in the case of the 

 female to make a hole for 

 the reception of the eggs. 

 The larvae are small, white, 

 legless grubs, with curved 

 cylindrical bodies. The 

 larvae mine under the bark 

 and form winding galler- 

 ies, gradually increasing in 

 size, which extend through 

 the inner bark and some- 

 times score the sapwood. 

 Each mine ends in a pupal 

 cell constructed partly in 

 the bark but mostly in the 

 sapwood. This cell is oval 

 in outline and is lined with 

 excelsiorlike shreds of 

 w^ood fiber. The nearly round larval mines and the "chip cocoons" 

 are characteristic features of their work. 



The adults are long lived and may deposit their eggs over a con- 

 siderable period of time. The larvae, which reach maturity rapidly, 

 usually within 2 or 3 months, may overwinter in the galleries or 

 transform to adults that either overwinter under the bark or emerge 

 and hibernate in the ground. There usually is but one generation 

 annually. 



Artificial control of the species in western forests has never been 

 found necessary, as they are usually held in check by natural enemies 

 and the limitation of suitable breeding material. 



Bark weevils of the genus Pissodes that are most commonly found 

 breeding under the thick bark at the base of small conifers, and the 

 hosts in which they breed are as follows : 



Figure 69. — Yosemite bark weevil {Pissodes yosem- 

 ite Hopk. ) Typical work and adults. Natural 

 size. 



