A BARK BEETLE. 1 25 



detecting and naming an offending insect. In the case of 

 C. abietis this is made difficult by the frequency with which 

 the galleries are rendered confused and irregular through over- 

 crowding. 



Foresters are generally acquainted with the under bark 

 workings of several bark beetles, particularly with the pine 

 beetle, Myelophilus pi/iiperda, in which one strong mother gallery 

 is formed. The galleries of C. abietis are different. These 

 circle round the base of a branch or twig, which, according to 

 its size, may or may not be completely girdled by one gallery. 

 The species is monogamous, and the female does most of the 

 work in cutting the gallery, which generally varies in breadth 

 inversely to its length. This working occurs only on the inner 

 bark layers, and the size is said to average f inch in length by 

 \ to y"^ inch in breadth. The male gives some assistance in 

 widening the gallery, although his chief help seems to be in 

 clearing out the fine bore dust. The gallery is completed in 

 five to seven weeks. Egg-laying proceeds in a different manner 

 from that of the pine beetle, where small notches are made for 

 the reception of the eggs. Cryphalus abietis makes no notches, 

 and the eggs usually occur in batches. The newly-hatched 

 larvae burrow along the sides of the mother gallery for some 

 time, but they ultimately separate, each one forming its own 

 tunnel. These early gnawings of the larvae often change the 

 appearance of the mother gallery to such a degree as to render 

 it unrecognisable. 



The larval galleries are cut almost at right angles to the 

 mother gallery. On the main branch they are sometimes verti- 

 cally up and down, at other times they run obliquely ; often 

 they run along the girdled branch or twig. When nearing 

 pupation the larva usually cuts into the outer surface of the 

 sapwood, but, prior to this, whether it cuts into the sapwood or 

 not depends on the thickness of the bark. The investigator 

 found, for instance, that the galleries cut immediately before 

 pupating and the pupal pit were, as a rule, the only traces on 

 the sapwood, but " where the bark was somewhat thick, as in 

 the case of strong branches, the larval galleries did not groove 

 the sapwood at all, and usually on these branches pupation took 

 place in the bark." Thin-barked branches and twigs, when 

 infested, show the larval galleries grooved in the sapwood and 

 a marked pupal chamber. After they emerge, the young 



VOL. XXXIII. PART II. K 



