CHERMESID^ IN RELATION TO BRITISH FORESTRY. 13I 



19. Chermesidae in Relation to British Forestry. 



( With Fiates.) 



By H. M. Steven, B.Sc.( Forestry), Carnegie Research Scholar in 

 Entomology, the University of Edinburgh. 



I.— INTRODUCTION. 



The Family Chermesidae possesses several well-marked 

 features. 



{A) The species are exclusively enemies of coniferous trees. 



{B) Normally two hosts and a period of two years are required 

 for their complete development. When two hosts are necessary, 

 one of them is always a species of spruce (genus Picea), 

 while the other may be a species of pine (genus Pinus), larch 

 (genus Larix), or silver fir (genus Abies) ; there is an American 

 species attacking Douglas fir (genus Pseudotsuga). The spruce 

 is called the Primary Host, and on it a gall is produced. The 

 other trees are termed Intermediate Hosts ; no gall is produced 

 on any intermediate host. 



(C) As in other Aphids all the individuals of a species are not 

 of the same form, but a series of generations follow one another, 

 each being more or less different from the one which produced 

 it. The following are the generations found in the Family 

 Chermesidae : — 



(i) Fundatrix Generation. — The first-stage larva hatches in 

 autumn. It settles on or near a spruce bud, secretes " wool," 

 from dorsal wax-glands for protection and passes the winter. 

 Development is completed in spring, and the adult lays a large 

 number of eggs. This generation consists entirely of females, 

 which are wingless in all stages. Its feeding habits cause the 

 needles of the opening bud to be stunted and swollen. 



(2) Gallicola Generation. — The larvae crowd amongst the 

 swollen needles, and as a result of their feeding a more or less 

 compact gall is formed. When these larvae have reached the 

 nymph stage, rudimentary wings being present, the gall dries 

 and opens. The nymphs climb out, moult, and become winged 

 adults. This generation consists entirely of females. The 

 Gallicolae may settle on the spruce, giving rise to Generation I., 

 Gallicolae non-migrantes, or may migrate to the needles of 

 the intermediate host, Gallicolae migrantes, and there lay 

 eggs. 



