314 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
progresses, the part of the tunnel behind is left stuffed with bore- 
meal. When full-fed, the grub pupates in a chamber at the end 
of its tunnel, and when the wood-wasp is fully developed it 
gnaws the circular hole by which it emerges. If too great a 
thickness of wood separates the adult wood-wasp from the out- 
side, the insect dies. In my specimens, in several instances, the 
adults ate their way out through half an inch of wood (indeed, I 
am inclined to believe that this is a fairaverage); but on splitting 
the pine log in November (all my specimens having issued in 
August from the log kept in the open air) I found two dead 
juvencus ata depth of | inch. The flight-time of the adults is 
from July on to August and September. Wood split in the 
winter, however, has revealed living adults, which might probably 
have issued in the next spring. 
There is a lack of experimental evidence as to the length of 
time elapsing from the egg-laying till the appearance of the adult 
insect. It seems certain, however, that the generation is never 
less than two years, and it certainly is often longer, there being 
cases on record where the adult wasps have issued from worked 
timber forming floors, etc. 
The larve are known to have bitten through lead piping. It is 
related that at the time of the Crimean War, bullets were found 
to have been pierced by larvee which had emerged from the 
unseasoned wood of the ammunition-boxes; and Blandford tells 
of the boring of S. gigas grubs from the timber supports into the 
lead chambers of sulphuric acid works, with a loss of acid. 
Preventive and Remedial Measures.—For egg-laying sickly 
grown trees are chosen, or such as have been accidentally 
wounded. These should be uprooted and removed. I am 
sorry to say that it is not very uncommon to find trees lying 
in the wood with many exit-holes showing all down the stem, 
whence scores of wood-wasps have issued to their work of 
destruction, Attacked stems are often rendered useless for 
technical purposes, the wood being quite honeycombed with 
larval galleries. Felled barked trees allowed to lie are also used 
as breeding-places. 
DipLosis PYRIVORA (Riley), the Pear Midge. 
This insect, the Cecidomyia nigra of Meigen, appears un- 
fortunately to be spreading in Britain. In the month of June 
I received some pears sent by Mr A, C. Forbes, Bowood, 
