Insects Bred from American Larch 47 
one brood.” We agree thoroughly with this statement. In 
New York it is within the possibilities for two or even two 
and a half generations to occur in one season but under field 
conditions it is doubtful if this possibility is ever realized. 
It is certain that a single generation is the rule and that 
occasionally a partial second generation is to be found — 
‘this second generation wintering over as partly grown larve. 
In larch, adults have been taken from under the bark on 
February 9, 29, April 22, 29, and October 24, and have been 
bred out in cages throughout the latter part of May and the 
early part of June. Larve were obtained from beneath bark 
April 22, 29, and October 24. In the Adirondacks the eggs 
of the main generation which has wintered over in the adult 
stage are laid throughout June, the exact date at which 
laying begins being of course dependent upon the season and 
varying from year to year. 
P. rufipennis is associated with a great variety of other 
insects, borers, predators and parasites — the actual rela- 
tions sometimes being quite close while in other cases they 
are quite remote. The scolytids Dendroctonus simplez, 
Eccoptogaster jicew, the cerambyeid, Phymatodes dimidia- 
tus, and the two siricids, Urocerus albicornis and Sirex 
abot are often associated with P. rufipennis throughout 
their life history. Of these the four beetles are inhabitants 
of the bark and therefore are influenced by each other much 
more than they are by the siricids which spend their larval 
life in the wood entirely. In general perhaps, each of these 
bark-inhabiting species is influenced adversely in that their 
food is limited by the presence of the other. However, under 
some conditions the association may be of mutual advantage. 
For instance it is apparently true that P. rufipennis is ordi- 
narily unable to breed to advantage in a living tree yet when 
such a tree is attacked simultaneously by D. simplex, P. 
rufipennis and EF. picew, or by the first two of these, its 
resistance is more readily overcome and it not only serves 
as a more favorable breeding place for these forms but for 
others as well. It is believed the D. simplex is able to kill 
weakened larch unaided but no cases were observed where it 
