1927 ] 
Observations on Wood-boriny Insects 
85 
Conclusions. 
The size of the present collection is of course very small 
but it allows one to draw several conclusions relating to the 
composition of the insect fauna that is associated with the wood 
of dead trees; conclusions, it may be added, which are sub- 
stantiated and supplemented in detail by the vast array of ac- 
cumulated literature relating to forest insects. 
a) In the first place, there are many species, particularly 
Coleoptera and phytophagous Hymenoptera which develop di- 
rectly in the wood or beneath the bark of logs. 
b) Among the parasitic Hymenoptera there is a series of 
species which prey upon these xylophagous beetles and other 
Hymenoptera. Very similar to these are certain predatory 
forms, especially beetles which depend upon particular host 
species for food. 
c) There are further many mycetophagous species, mainly 
beetles, which develop in the several types of fungi regularly 
associated with decaying wood. These likewise support a series 
of parasitic forms. 
These three ethological groups we may regard as constitut- 
ing a primitive fauna which has long been characteristic of wood. 
A small proportion occur in living trees, but such a great majority 
live in the wood of moribund or dead trees that we must believe 
the latter habitat to present the most primitive one. In the case 
of the mycetophagous types this is still more evident. 
d) A secondary fauna includes first a number of predatory 
insects which are not like the parasites and predators previously 
referred to, associated with particular hosts, but find simply a 
convenient source of food supply in the xylophagous fauna. 
e) Other members of the secondary fauna include various 
insects, such as wasps and bees that find suitable nesting sites 
in burrows in the wood. Although such habits are firmly fixed in 
one or two families, they are clearly not of primary general 
significance. 
f) Finally, as in any biocoenose there are forms on the 
borderland whose occurrence is either wholly chance, or at least 
very occasional and due to sporadic combinations of circums- 
