Insects Bred from American Larch 75 
a pupation chamber. It usually continues this burrow paral- 
lel to the surface for about 40 to 50 mm., then extends it 
upward to a point just beneath the bark. The pupal cham- 
ber for about half its length is solidly packed with fine frass, 
as was the entire larval burrow. However, the “ sawdust ” 
in the entrance to the pupal burrow is of a lighter color 
than that in the larval mine, because it is derived entirely 
from the sapwood, whereas the latter comes partly from the 
bark. The adult on arising gnaws through the thin layer 
of sapwood left by the larva, perforates the bark and emerges 
through an oval exit hole about 2144 by 3 mm. in diameter. 
The following borers were associated with L. sex-guttatus: 
Polygraphus rufipennis, Eccoptogaster picew, Pogonocherus 
nuxtus, Neoclytus longipes, Phymatodes dimidiatus, Mela- 
nophila fulvoguttata, Chrysobothris blanchardi, C. sea- 
signata, C. dentipes, and Anthaxia quercata. All of these 
except the two scolytids and P. dimidiatus are two-year forms 
and live in the limbs and tops during the same two seasons. 
P. rufipennis and EL. picee are associated with these larger 
borers usually only during the first year. Occasionally, 
however, second broods of each of these are reared in the 
old host. Although this may perhaps occur more commonly 
in the breeding cages than in nature, examples under both 
conditions were found. The brood of either of these scolytids 
is likely to be robbed of their food or actually killed outright 
by the larve of Leptostylus sex-gquttatus or any of the other 
round-headed or flat-headed borers mentioned above. ‘This 
is especially true during the second year of the larval life 
of the large forms. In this connection it is interesting to 
note that two sister species of L. sex-guttatus, L. aculipes 
and LZ. macula, have been reported in similar roles in con- 
nection with two other scolytids (Schwarz, 1890, p. 165). 
The inter-relations of the larger borers are variable and 
more or less accidental. The simultaneous presence of sev- 
eral specimens either of the same species or of different 
species in the same region may be of advantage in over- 
coming the resistance of the dying or weakened-tree. If the 
tree is already so weakened as to offer no considerable danger 
