Insects Bred from American Larch 33 
carefully removed, bit by bit, forty-five cocoons were exposed 
in one lot consisting of a piece about six inches in diameter 
and two feet long. Nine of these were twelve mm. or more 
in length and all the rest were below ten mm. Several of 
the latter were about nine mm. long and all of the rest smaller 
than 7.5 mm. The smaller ones were found in the burrows 
of P. rufipennis only and were doubtless the cocoons of 
Spathius tomict which had emerged the previous season 
before the material was brought to the laboratory. The 
cocoons of the two larger sizes, however, were found only in 
the burrows of P. dimidiatus, although careful search was 
made in the burrows of other species in both the wood and 
in the bark. The identity of these burrows was absolutely 
established by the finding in several of the pupal chambers of 
dead adults which had never emerged. In the same pupal 
chambers were found the cast larval skins, the mandibles and 
head armature of which are quite characteristic. Close to 
each of the parasitic cocoons, the larval remains of the host 
were found and these on comparison with the larval casts 
found in pupal chambers containing dead adults of P. dimi- 
diatus established absolutely the identity of the parasitized 
form. 
By comparing the sizes of the adult hymenoptera taken 
from this material it was readily established that Rhyssa 
lineolata and Pseudorhyssa sp. come from the larger cocoons 
in the burrows of P. dimidiatus (the cocoons of the two 
being indistinguishable) while the species of Doryctes and 
probably also Odontaumerus canadensis came from the 
cocoons about eight to nine mm. long, found in the burrows 
of the same borer. 
The Upper Trunk in Dying or Recently Killed Larch Trees 
contained the same borers with several exceptions as did the 
lower trunk. Those occurring in this region include the 
scolytids — P. rufipennis and FH. piceae and their predators 
— P. dislocatus and C. bicolor, and parasites — Spathius 
tomict, Spathius sp., Spintherus pulchripennis, Phasgono- 
phora sp., Cheiropachus sp. and Heterospilus sp.; the 
2 
