CHERMESID/E IN RELATION TO BRITISH FORESTRY. 149 



in this country, but any appearance of Chermcs on Douglas fir 

 should be investigated, as it is highly desirable to conserve 

 the relative immunity to disease which this conifer enjoys in 

 Europe. I have also suggested a new method of control for 

 these pests. This method aims at the destruction of the 

 Chermesidie before the conifers are dispatched from the forest 

 nursery. This would ensure that the further distribution of 

 these pests would be limited, and that the plants would get a 

 chance to establish themselves in their new environment. This 

 method should be specially applicable in this country, where 

 extensive replanting will have to be carried out after the war. 



1. Damage to the Hosts. 

 {a) Spruce. 



(i.) Genera Chermes, s. str., and Cnaphalodes. — The sucking 

 of the Fundatrices and Gallicolae of the species of these genera 

 cause the buds of spruce to be galled. Chermes abietis (Kalt.) 

 and Ch. viridis (Ratz.) attack strong, growing buds, hence the 

 damage is primary. In most cases the growing point is not 

 killed, the shoot grows on, but is usually bent, and sometimes 

 it dies in the following year (Plate II. Fig. i). Ciiaphalodes 

 lapponicus (Choi.) and Cn. strobilobius (Kalt.) attack buds of 

 thin, shaded branches, hence the damage is secondary. In most 

 cases the growing point is killed, so that the gall terminates 

 the twigs (Plate II. Fig. 2). The species of Chermes, s. str., 

 usually attack the tree first, then as the tree becomes weakened, 

 or the lower branches shaded, suitable food material for the 

 species of Cfiaphalodes is provided. My observations showed that 

 the non-migrating species, Ch. abietis (Kalt.) and Cfi. lappofiicus 

 (Choi.), did more damage to spruce than did the migrating 

 species. The increase of these non-migrating species on a tree is 

 very rapid once infection takes place. The damage done by the 

 species of the genera Chermes, s. str., and Cnaphalodes is not 

 serious when the spruce are healthy, but allied with unsuitable 

 soil or atmospheric conditions, or both, the species of these 

 genera, and especially the non-migrating species, may do serious 

 damage to spruce. 



(ii.) Genera Dreyfusia and Pineus. — Dreyfusia Niisslini and 

 Pineus pini produce galls on Picea orientalis. This conifer has 

 not proved itself to be of silvicultural value in this country, 

 hence the damage done to it need not be considered. 



