1899 - 1900 .] Dr R. Stewart MacDougall on Genus Pissodes. 319 
The Biology of the G-enus Pissodes. (George Heriot 
Besearcli Fellowship Thesis.) By R. Stewart MacDougall, 
M.A., D.Se. Communicated by Professor Cossar Ewart. 
(Read June 4, 1900.) 
In the case of any harmful insect of economic importance, in 
order to war against it, or apply remedial measures at all intelli- 
gently, a knowledge of the life-history of the pest is necessary. 
This proposition will, I think, meet with such ready acceptance as 
to render proof unnecessary, but I might in illustration mention 
two cases which came under my own observation, where in the one 
case a knowledge of the round of life of the attacking insect saved 
a whole forest, and in the other proved of great importance. 
There is a large moth, not uncommon in the pine woods on the 
Continent, viz., Gastropachi pini (Ochsh), whose caterpillars some- 
times do enormous damage by stripping the pines of their needles. 
Some years ago there was a plague of these moths in the extensive 
Eoyal Forest near Niirnberg, in Bavaria. The moths had laid 
their eggs in July on the needles and branches, and the caterpillars 
which hatched out had fed in tens of thousands on the trees during 
August and September. They left the trees in October and 
November to pass the winter in sheltered places under the moss 
and litter of the forest. As a point in their biology, it was known 
that in the following March they would come out of their hiding- 
places and reascend the trees to complete their growth. A ring or 
circle of very sticky tar was therefore placed round each tree in 
the month of February. The result was that the caterpillars, 
endeavouring to ascend the trees after the winter’s rest, were 
brought to a halt at the rings, which they would not cross, and her© 
they were massacred in their thousands, and the forest saved. 
In another part of Bavaria, where in 1890-91 the attacks of the 
caterpillars of the Nun moth ( Liparis monacha) on spruce cost the 
Government £100,000, a new point in the biology, which had 
escaped notice in the previous devastations of this moth, came 
