194 FOREST ENTOMOLOGY. 



and. may be considered one of the most remarkable gall-growths 

 arising from insect agency, which causes modification in the vegetable 

 organism. It may originate either from a bud or leaf. First of all, 

 we get a very sudden "moss-gall," and each hair is a beautiful 

 feathered structure. ' Later on we get a conglomeration of woody 

 cells, varying in number from three or four to thirty or forty. Each 

 cell contains a single grub ; the interior is smooth and clean, and. the 

 outside hardy and woody. The growth is complete by the end of 

 August, and the first flies appeared in confinement June 9, 1901, 

 Northumberland, and again on July 9, 1906. 



Megastigmus spermotrophus, Wachtl. 



This insect, both in point of damage and structure, is entirely 

 different from all the other genera and species belonging to the order 

 Hymenoptera which we have been hitherto considering. 



It is the only known hymenopterous insect directly injurious to 

 the seed, and it belongs to the sub-order Petiolata, which are char- 

 acterised by a constriction between thorax and abdomen. To this 

 order belong the bees, Avasps, and ruby flies, and a large series known 

 as the Parasitica, of which a very large number of examples may 

 be found from parasites bred froiu the various species of oak galls. 

 In fact, Cameron gives species of INIegastigmus as parasitic on several 

 species of galls. 



This insect has been very fully worked out by Dr R Stewart 

 MacDougall,-^ by whose kind permission I herewith give the follow- 

 ing notes from his valuable paper. 



The damage was first discovered by Mr John Crozier, forester, 

 Durris, near Aberdeen. So far as Scotland is concerned, Durris 

 may be almost called the home of the Douglas fir, and therefore ]\Ir 

 Crozier wrote in the following terms to Dr MacDougall : — 



"The insect has, for some years back, been causing a serious loss 

 to our stock of Douglas tir seed. I noticed its presence on coming 

 here nine years ago, but it had no doubt been in the estate before 

 that time. Seed was plentiful, however, and as the damage was 

 comparatively trifling I did not pay much attention to the fact. 

 Now, however, it has assumed a more serious aspect, as the seed 



^ Transactions of the Royal Scottish Arboricultural Society, 1906. Vol. xix., 

 Pt. I., p. 52. 



