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The Genus Chermes. 



[SEPT., 



Life History of Chermes viridis * Ratz. 



The primary host is the Spruce (Picea). The intermediate host is 

 the Larch (Larix). 



Description of Gall. — The gall on the Spruce looks like a miniature 

 pine-apple or a small cone. The foundress has her proboscis sunk in 

 the base of the bud, and as a consequence the shoot and the base of 

 the young needles swell and the needles meet at their edges. The 

 green tips of the needles project above the galled portion. The gall 

 is pale green or bleached in appearance. Sometimes the fused edges 

 of the lower swollen parts of the needles are reddish in colour, and the 

 gall has a mottled appearance. Typically the gall is one-sided, the 

 shoot not being affected all the way round; the shoot also grows 

 beyond the gall (occasionally there is no growth beyond the gall). 



Generation i : The Foundress. — A larval Chermes, hatched from a 

 fertilised egg, anchors itself in the autumn by sinking its long proboscis 

 of bristles into the base of a Spruce bud. In this position the dormant 

 larva — not very noticeable as it rests protected on the underside of 

 the bud — passes the winter. In the next spring the awakened larva 

 begins to feed, and by the end of a month and after three moults is 

 the adult foundress. This foundress is very small, and is oval in 

 shape and green or dark green in colour; the antennas are three- 

 jointed. From chitinous glandular plates on the upper surface of the 

 body a wool or wax is secreted, and in spring the position of the insect 

 may be indicated by the speck of white wool. 



The foundress generation consists exclusively of wingless females, 

 which lay round them little heaps of green or dark green eggs that 

 are fixed by means of delicate stalks. After egg-laying, the foun- 

 dresses die. From the eggs hatch greenish-yellow larvae, which 

 develop into Generation 2. 



Generation 2 : The Winged Migrants.- — These larvae have short 

 probosces, three-jointed antennae, and no woolly excretion, and become 

 enclosed in the chambers of the gall formed by the swollen bases of 

 the needles that have become fleshy and scale-like (the gall having 

 arisen as the result of the sucking of the foundress), and, thus pro- 

 tected, develop to the nymph stage. In this nymph stage, character- 

 ised by wing-sheaths, the insects issue from the gall in July, the 

 chambers of the gall having opened owing to the drying of the gall. 

 The nymphs are red-brown in colour, and after a fourth and last 

 moult become adult. 



The adults of this 2nd Generation are all females, and are winged. 

 They are reddish or yellow-brown in colour, and have five-jointed 

 antennae; there is also a slight woolly excretion on the upper surface. 

 The wings are four, held sloping like the tiles of a house, and the 

 hind pair are smaller. 



These winged adults of Generation 2 fly to the Larch, and on 

 the Larch needles lay dark green eggs. From these eggs the larvae 

 which will develop into Generation 3 hatch in the autumn. 



Generation 3 : The Colonists. — The larvae from the eggs on the 



* Chermes abietis Linn, includes what are now known as C. viridis Ratz. and 

 C. abietis Kalt. 



