3 77 
*1916-17.] The Family Chermesidse. 
In addition to these experiments, a considerable number of spruce and 
larch, 2 year 1 year old, not so badly infested with Chermesidae, hence 
healthier plants, were fumigated, as were the plants in Experiment 3. The 
fumigation was in this case completely successful. 
In the opinion of the author, Experiments 1-5 were not completely 
successful as regards larch, because the plants of this conifer were farthest 
from the generator during fumigation, and the concentration of the 
fumigant around them was too weak owing to the fumigation box not 
being sufficiently gas-tight. No reason can be given why Experiment 7 
was not successful as regards spruce. 
The temperature at which the fumigation of these pests by hydrocyanic 
acid gas was successful is much lower than that considered the optimum. 
This is important, as the average air temperature, at the time when fumiga- 
tion must be carried out, is low. 
These experiments have shown that fumigation is a safe, efficient, and 
cheap method of killing Chermesidae on nursery stock. The practising 
of this method of control will ensure that the further spread of these 
pests will be limited, and that the conifers will get a chance to establish 
themselves in their new environment. The methods will have to be 
improved before a definite set of instructions can be given, but the 
following may be stated now : — 
(a) The fumigation should be carried out immediately before dispatch 
of the plants to the planting area. 
(b) The fumigation should be carried out not later than the 1st April, as 
the insects begin to become adult and lay eggs after that date. 
(c) Hydrocyanic acid gas, generated from potassium cyanide at the 
rate of 1 oz. to 100 cubic feet of space, or from sodium cyanide 
at the rate of 1 oz. to 130 cubic feet of space, appears to be 
the most useful fumigant. 
This method of control should prove of especial value in this country at 
this time, as very extensive planting of conifers will have to be carried 
out in the years following the close of the war. 
Part III. General Conclusions. 
1. The non-migrating species of the genera Chernies s. str. and 
Cnaphalodes are more serious enemies to spruce than are the 
migrating species. The species of Chermesidae, however, are 
only serious enemies of spruce when allied with unsuitable 
soil or atmospheric conditions. 
