1927] 
Observations on Wood-boring Insects 
87 
lection without having recourse to other well known instances. 
Among the several extensive and diversified modern orders of 
insects, including the Coleoptera, Lepidoptera, Hymenoptera 
and Diptera, all of which are traceable to an origin from an 
earlier Mecopteroid type the occurrence of dendrophily is well 
marked in several of the primitive families. Among the Tri- 
choptera wood-boring larvae are of rare occurrence, no doubt by 
reason of the fact that the developmental stages are almost 
without exception aquatic. However, in the other orders there 
are numerous and widely scattered examples of xylophagous 
habits, and with the exception of the Coleoptera, the wood- 
boring forms are mainly members of the more primitive families. 
A reason for the general absence of the more primitive beetles in 
this habitat is not far to seek since this group is the oldest of the 
series. It is represented by several types in the Upper Permian 
and in the Upper Trias had become quite prevalent, so that if the 
association of beetles with trees dates from this time or later 
there were various types of Coleoptera extant. The oldest Hy- 
menoptera known have been found in the Upper Jurassic and 
are very similiar to living members of the archaic family Siricidse 1 
Whether the order existed in the Upper Permain appears very 
doubtful, as the only insects so far discovered which appear to 
be in any way related to the modern Hymenoptera are the order 
Protohomoptera found by Tillyard in the Upper Permian of 
Kansas. Insects supposed to be Lepidoptera have been reported 
from the Middle Jurassic but these have been shown without 
question to be Homoptera, so that no Lepidoptera are actually 
known earlier than the Tertiary. This is obviously due to in- 
complete knowledge and to judge from their food relations at 
the present time as outlined in the present account, it seems 
probable that the Lepidoptera were present in the Liassic and 
probably in the Triassic. This order is thus apparently older 
than the Hymenoptera but of more recent origin than the Col- 
eoptera. The Diptera are well represented in the Upper Liassic, 
1 Since the above was written I have received a paper by Martynov 
(Bull. Acad. Sci. Russie, vol. 19, 1924) in which several remarkable Hymen- 
optera are described from Jurassic deposits in Turkestan. These include a 
very primitive type of sawfly, an oryssid-like genus and a member of the 
family Heloridse. These discoveries offer strong confirmation of the views 
expressed in the present paper. 
