GALLS INDUCED BY PLANT-LICE St 



needles, and here undergo the fourth and last moult, casting 

 off the pupal skin, which is left attached to the needles. 

 The winged insects, or Alatae, are all non-migratory females 

 They are yellow, with black head and upper thorax, and 

 always have the third joint of the antennae distinctly shorter 

 than the fourth, an important point in diagnosis. These 

 winged females lay their eggs at the base of the buds, and 

 die. From these eggs arise the Fundatrices, and the life- 

 history as above set forth begins anew. Particulars as 

 regards the length of time the production of unisexual 

 generations may continue are wanting ; there is evidence, 

 however, that it may extend over four years. At one time 

 it was thought there was no male, but Blochmann and others 

 have shown that this idea was erroneous. 



More than twenty years have elapsed since Blochmann 

 announced the existence of a sexual generation in Chermes. 

 Subsequently, Blochmann, Dreyfus, and Cholodkovsky, dis- 

 covered, independently, the periodic migration of one 

 generation from the Spruce to the Larch, and the return 

 of a later generation the following year to the Spruce. 

 Later, Cholodkovsky discovered the phenomenon known as 

 "parallel series "in connexion with the generation on the 

 larch. It has been investigated chiefly in this country by 

 Burdon. His valuable paper,* entitled " Some Critical 

 Observations on the European Species of the Genus 

 Chermes," is indispensable to all workers in this difficult 

 genus, as it contains tables of the results of Cholodkovsky's 

 investigations. 



Even the casual observer of the " Pineapple " galls on 

 the Spruce cannot fail to note that they present marked 

 differences in size and colour, and that some open much 

 earlier than others. The largest of these galls is attributed 

 to Ch. viyidis, a species which is the "double " of Ch. ahietis ; 

 it was formerly regarded as a variety of it. The Fundatrices 

 and the Alatae differ from those of CA. ahittis in the darker 

 colour (some shade of green) and the green eggs. The 



* Jourtt. Econ. Biol,, 1908, vol. ii., No. 4. 

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