Section IV., 1910. [95] Trans. R. S. C. 
VII.—Observations on the Parasitism of Isaria farinosa (Dicks.) Fr. with 
special reference to the Larch Sawfly (Nematus erichsonii Hartig). 
By H. T. Güssow, Dominion Botanist. 
(Communicated by Dr. Wm. Saunders, F.R.S.C., and read 27th September, 1910.) 
The fungus on which I wish to record a few observations is, as no 
doubt you are aware, one of the commonest of those found growing on 
insects, at some time or other during different stages of their develop- 
ment. Far greater importance has been attached to these entomogenous 
fungi in recent years owing to their being regarded as natural factors 
in the control of insect pests. This question has interested both Ento- 
mologist and Botanist alike and, owing to the alarming increase at the 
present day of the larch sawfly on both sides of the Atlantic, a special 
study of this particular fungus has been made more opportune. There 
were several points of interest on which further research was desired. 
Was the fungus known to occur on the larch sawfly cocoons in Europe 
identical with that observed in Canada? This is, however, one of the 
minor points at issue. Still more prominent was the question—Does 
this fungus attack the living cocoons, or the pupating larve or is it 
only secondary, growing saprophytically on the dead cocoons? The 
third point of interest was to ascertain how infection took place. 
I. 
The first point was easily settled. Material i.e. larch sawfly 
cocoons collected by Dr. C. Gordon Hewitt in Canada, showed small 
patches of a whitish fungus growing on the surface. The cocoons were 
kept under suitable conditions for further study of the fungus. Some 
three weeks later the growth had become elongated and had taken the 
shape of the characteristic forked or tongued sporophores with which 
the investigator is quite familiar. These measured from 2-3 centimeters 
in length; their stalks were orange coloured at the base and about 
two-thirds of the upper portion was covered with a white farinaceous 
mass. On microscopic examination of these filaments the fungus was 
identified as belonging to the genus Jsaria, being the conidial form of 
the ascigerous (pyrenomycetous) fungus Cordiceps militaris. To estab- 
lish, however, the identity of the Canadian species with the European 
one it was thought advisable to make a series of pure cultures. I 
succeeded, with the necessary care, in obtaining immediately a pure 
culture by removing a small portion of the farinaceous mass composed 
of spores by means of a sterilized platinum needle. The spores at that 
