118 ME. E. P. STEBBING ON THE LIFE-HISTORY OF 



The life-history of the insect on the Silver Fir wonld therefore appear to have heen 

 worked out with some completeness, were it not for the fact that during an autumn 

 tour in the Himalaya, made between the end of September and the middle of November 

 1906, I discovered dead winged individuals of this insect in some numbers on the under 

 surface of the Silver Fir needles towards the end of September and beginning of October. 

 Now these flies could not have occupied this position throughout the heavy monsoon 

 rains in July and August without getting washed off. A simple explanation for this 

 may be that they come from Spruce galls which had not opened before the monsoon 

 broke and which had only matured at this period. 



Failing such an explanation, it would appear possible that a generation of the apterous 

 females (Exsules) may lay eggs towards the beginning of September and that the winged 

 flies had arisen from a portion of these eggs. I could find no eggs upon the trees. 



Summary. 



We may summarise this portion of the life-history as follows : — 



In the early spring egg-masses covered with a woolly material are found on the bark 

 of the main stem and branches of saplings and on the branches of older trees. As the 

 young needles of the Silver Fir unfold from the buds these eggs hatch out and minute 

 grubs crawl up onto the young tender spring needles, insert their proboscides into the 

 tissue of the under surface of the leaf and feed there. In about three weeks, after several 

 (probably usually three) moults, the larger portion of these larvae mature as apterous 

 female insects, develop the white cottony material, and commence egg-laying. A portion 

 of the spring eggs, however, produce larvae which, when full-grown, are easily distinguish- 

 able from the apterous female larvae. These larvae or nymphs, which are to be found 

 much more rarely upon the trees, shed the last larval skin (this being the fourth moult) 

 and a winged insect emerges. These winged insects appear to mostly lay eggs on the 

 Silver Fir needles. It is possible, however, that a certain proportion migrate to the 

 Spruce. 



From this first generation of eggs laid about the third week in May new minute larvae 

 emerge in from 2-3 days and spread out over the Silver Fir needles now grown to some 

 length. They may be often seen thickly studding the needles as minute black specks, 

 looking rather like a fungus attack on the needles. 



From these larvae a second generation of apterous females may be developed in 

 favourable dry hot years. Usually, however, it will be observed that when the young 

 larvae are about a week old they collect down towards the bases of the needles and 

 feeding here set up an irritation which results in an exudation of turpentine, and also 

 causes the uppermost new needles of the year to curl up in a corkscrew manner, the 

 sticky excretions binding them together into a large twisted "bud." Within the cork- 

 screw " bud " larvae of two kinds will be found, the normal madder-brown coloured ones 

 and others with a yellowish tinge. The former develop into the apterous females and 

 lay eggs either on the needles below the corkscrew mass or on the stem below it. 



The yellowish larvae leave the corkscrew mass on becoming full-grown, the needles by 



