I907-] 



A Cause of Larch Canker. 



55i 



(3) spraying as soon as the leaves expanded with \ oz. liver 

 of sulphur to 1 gallon of water, the strength being increased 

 to f oz. per gallon as the leaves and young growth increased in 

 vitality. 



On the 24th October this plantation was inspected and no 

 disease was found ; neither was any disease found in any 

 plantation near or in any part of Ombersley on that date, noi 

 again in November. 



Among the problems which for some time have been engaging 

 the attention of those interested in the larch is the question of 



the agencies which play a part in the 

 Insect Agencies as a spread of the larch canker fungus. 

 Cause of Larch Canker. Certain insects, and among them the 



Psocidce, are regarded as being in one 

 sense a cause of the disease, as the fungus is able to gain an 

 entry to the tree by punctures or wounds made by the insect. 



Some species of Psocidce pass their time wholly among 

 various species of fungi and feed almost entirely upon the 

 minute vegetation. The various members of the Psocidce are 

 very small creatures which undergo a so-called imperfect 

 metamorphosis, being four- winged in their final or mature 

 stage. The species, which is specially referred to in this paper 

 is the Fungus fairy fly, Caecilius flavidus (Figs. 1 and 3). The 

 larvae from the eggs of this species are of very small dimensions 

 but increase to about one-tenth of an inch when the larval stage 

 is completed — that is to say, when they are ready to receive 

 their wings. In the mature condition the length averages 

 one-seventh of an inch, including the wings. The colours are 

 dull, indefinite brownish-grey with darker markings. The 

 head and thorax are very dark in the winged specimens. 

 Although these insects may be very alert they are often very 

 loth to make use of their wings ; even while being examined 

 in front of a strong light with nothing whatever to prevent them 

 from flying away they have failed to seek their freedom and it has 

 been necessary actually to dislodge one by a jerk from a needle-- 

 point before one has been able to examine it microscopically. 



Other writers have noted this occasional disinclination to 

 use the wings, the insects having been known to allow 



