154 TRANSACTIONS OF ROVAL SCOTTISH ARBORICULTURAL SOCIETY. 



silver fir and Weymouth pine. It appears to me from careful 

 observation that little or no good will follow any attempt to root 

 out these pests by arranging the silvicultural mixtures so as to 

 eliminate either of their hosts. 



The second question to be considered is the possible effect of 

 the substitution of exotic conifers, for those specially liable to 

 attack, in silvicultural mixtures. As has been stated, practically 

 all these exotic conifers have been attacked. Nevertheless, 

 conifers such as Japanese larch, Menzies spruce, and Corsican 

 pine are, at present, relative immune to attack by Chermesidse. 

 It remains to be seen, however, whether that relative immunity 

 will be retained by these conifers. In view of the very severe 

 damage which Dreyfusia Niisslini does to Abies ?iordmanniana 

 and A. pectinata, it is very necessary to seek a silver fir less 

 liable to attack to take the place of these silver firs in our 

 silvicultural mixtures. 



4. Control. 



I am convinced that there is no practical method of controlling 

 the Chermesidae once a plantation has been formed. Hence we 

 must take advantage of every method of controlling these pests 

 before and during the formation of a plantation, thus ensuring 

 that the subsequent damage will be at a minimum. 



We must first of all take advantage of silvicultural methods of 

 controlling these pests. These are two in number, namely : — 



(a) As the Chermesidje become serious pests whenever the 

 health of the conifers is impaired, great care should be 

 taken to ensure that the conifer or conifers chosen for 

 an area are clearly suited to the conditions of that area. 

 It should always be remembered that if the soil or 

 atmospheric conditions or both are inimical to the full 

 development of the conifer or conifers, then in all 

 probability, in a few years, the Chermesidae will also 

 have to be numbered among the adverse factors. 



{b) The use of suitable confers, other than those which are 

 the favourite hosts of the Chermesidae, has been 

 considered in the previous section. 



Secondly, we must consider what means can be taken to 

 ensure that the coniferous nursery stock, used in the formation 

 of a plantation, are free from Chermesidee. This will not ensure 



