92 College of Forestry 
show considerable variation not only in size but in coloration. 
In size the five males still in our possession vary from 12 mm. 
to 18 mm. The differences in coloration, which are quite 
striking, consist in a variation in the relative amount of 
yellow upon the antenne, abdomen and legs. 
Borers associated with U. albicornis are Polygraphus rufi- 
pennis, EHccoptogaster picew, Phymatodes dimidiatus, Serro- 
palpus barbatus and Sirex abbotu. As U. albicornis, which 
is typically a one-year form, attacks weakened, dying or very 
recently killed trees, its life history in the wood coincides 
with or overlaps that of each of these forms. The two 
seolytids usually enter the bark rather early in the same 
season, and are therefore likely to have been established a 
month or more before the eggs of the siricid are laid. 
P. dimidiatus, also a one-year form, probably enters the tree 
about the same time as the Urocerus, but as its burrows are 
entirely in the bark, the two forms have no direct or very 
definite relations. S. barbatus and Sirex abbotw are both 
wood-boring forms similar to U. albicornis, but the relations 
are never likely to be close. No case was observed where 
these various wood-eating larvee were present in such number 
as seriously to interfere with each other’s chances of obtain- 
ing food. The occupancy of the wood by the larvee of Sirex 
abbotit and of U. albicornis coincides nearly exactly. Ser- 
ropalpus, however, is a two-year form and its larvee may have 
lived in the sapwood an entire year before the advent of the 
other borers and during this time may have performed a 
very important function in overcoming the resistance of a 
weakened tree. 
While a number of parasites were bred from the same 
material as U. albicornis, no evidence of any close relation 
between them and the siricid was found, though many bur- 
rows were examined for cocoons. The predator Phyllobaenus 
dislocatus was obtained from the same material, but no 
reasons for believing it predaceous upon U. albicornis were 
found. 
