230 B. P. Stebbing — Life-History of Chermes abietis-piceae Steb. [No. 4, 



G. abietis-piceae closely resembles its European confrere 0. abietis- 

 laricis in the fact that the individuals of one generation may assume 

 different habits at different stages of their existence, and so set up 

 the phenomenon known as parallel series. Further different stages in 

 the life-history may be passed on plants of a different species, the host 

 plants in India being the Spruce and Silver fir instead of the Spruce 

 and Larch as in Europe. Blochmann, Drefus, and Cholokovsky have 

 made a series of the most important and interesting observations into 

 these habits in the case of the European species within the last two 

 decades or so, but the fact that a closely allied species lives in a some- 

 what similar manner on conifers in the N.-W. Himalayas seems to have 

 remained unknown until discovered by the writer in 1901. 



Before proceeding to describe in detail the stages as yet observed 

 in this complex life-history, I may briefly run over the points which give 

 rise to the phenomenon known as ' parallel series. ' 



In the early spring wingless $ of the Chermes are to be found upon the 

 Spruce trees, they probably having hibernated upon them through the 

 winter. These $ lay eggs from which shortly hatch out young larvae which 

 feed at the base of the young developing needles, causing them to swell up 

 and coalesce into a pseudo-gall within which the aphids become enclosed. 

 When fully grown about July the galls open, the larvae crawl out, moult, 

 and become fully developed winged insects. Some of them remain on the 

 Spruce and lay eggs on it. A portion however of this winged gall 

 generation leaves the Spruce and flies to the silver fir and lays eggs on 

 it on the bark of the twigs or stem. The parthenogenetic $ which arise 

 from these eggs either hibernate upon the trees and lay their eggs in 

 the early spring of the ensuing year, or lay the eggs in the autumn. 

 These eggs are covered with a white cottony substance which can be seen 

 in the form of white specks all over the branches, and often all over the 

 whole of the stems of young saplings. Each little white cottony mass 

 contains a large number of eggs. From these eggs hatch out in the spring 

 small larvae which crawl up on to the newly-developed young silver fir 

 needles and feed by sucking out the sap from them. It would appear that 

 whilst some of this generation go on to the winged form, others remain on 

 the needles and mature and lay eggs on them without ever acquiring wings 

 or leaving the tree. A part of this generation, however, always acquires 

 wings about the beginning of July, and these winged insects then fly to 

 the Spruce tree and lay their eggs on the bark of the stem (in young 

 trees) or branches. 



My observations in the case of the Indian species seem to prove that 

 either form in the two series can remain for a prolonged period on the 

 one host tree before producing the winged generation which enables it to 



