605 



Chrystal (R. N.) & Story (F.). The Douglas Fir Chermes [Cherme^ 

 coole.yi). — Forestry Commiss., London, Bull. 4, July 1922, 50 pp., 

 9 plates. [Received 9th October 1922. J 



A study has been made of Chermes cooleyi, Gill., an American 

 species that has lately been noticed damaging Douglas fir in Britain. 

 A general account of this Aphid is given as occurring both in America 

 and in Britain, and biological and morphological keys to the British 

 species of the genera Chermes, Gillettea and Cnaphalodes are appended. 



The following summary of the investigation is given by the 

 authors : — C. cooleyi, Gill., hibernates upon Douglas fir as a first stage 

 larva. Development commences in early spring, and the first mature 

 stem-mothers may begin oviposition early in "April. This brood is 

 dimorphic, about half of the young developing into winged migrants, 

 and the rest into wingless forms on Douglas fir [Pseudotsuga taxifolia]. 

 The winged migrants mature about the beginning of May, and fly to 

 Sitka spruce [Picea sitchensis], settle on the needles, and lay a small 

 number of eggs. From these eggs hatch the larvae of the sexual 

 generation. This generation has not hitherto been described for 

 Chermes cooleyi either in Europe or America. Both male and female 

 sexual forms have been found in Britain, but they have failed to 

 produce offspring. No gall stage on the Sitka spruce has been found, 

 and no winged gall form has been observed settling on the needles of 

 the Douglas fir. There are two broods on the Douglas fir, an early 

 summer brood and a late summer one, which remains on the needles 

 as first stage larvae over the winter. 



The species is widely distributed in the south and west of England, 

 and is recorded from a few localities in the midlands and north. In 

 Scotland its distribution is local, and it is so far unknown in Ireland. 

 It has been present in Britain for a number of years, and was un- 

 doubtedly introduced on nursery stock, by which means it is now 

 very largely spread. Wind dispersal is, however, known to occur, 

 and other means of infection are not unlikely. The insect has not 

 so far proved a serious enemy of the Douglas fir in established planta- 

 tions. In consequence of its being confined solely to the needles, it 

 has not the capacity for damage that is possessed"^ by Chermes {Drey- 

 fiisia) niisslini, Ratz., on silver fir. Its importance as an enemy of 

 plants in the nursery and in newly-formed plantations is uncertain. 

 The amount of woolly secretion visible on infested trees in any given 

 area bears no relation to the amount of damage done. 



The natural enemies of this Aphid do not seem to play a prominent 

 part in its control. Artificial measures can only be employed in the 

 case of nursery plants and ornamental trees. 



For use in nursery beds the authors recommend a spray of f to 1 

 fluid oz. of 98 per cent, nicotine and I lb. soft soap in 10 gals, water, 

 1 fluid oz. of this mixture being diluted with 1 pint of soft water before 

 use. A fine force sprayer should be used, and the lower surface of the 

 needles should especially be treated. An alternative emulsion con- 

 sists of 2 pints paraffin with 1 lb. soft soap in 10 gals, water. Young 

 plants may be dipped in a solution of 1 lb. soft soap to 1 gal. water, 

 but this is not recommended where other means are available as the 

 plants may suffer from heating in transit. Experiments in the 

 fumigation of infested nursery stock have as yet given inconclusive 

 results. 



