INSECTS INJURIOUS TO CONIFERS. 



175 



should be remembered that a better protection than separation 

 by a mere open space against the immigration of these insects 

 from distant trees is afforded by an intervening belt of trees of a 

 different species, as, for example, deciduous trees. If anyone who 

 has been troubled with the Spruce-gall aphis and the Larch-bug 

 in his plantation will endeavour to make separate nurseries of 

 the two trees, isolated in clearings of deciduous trees, his expe- 

 rience of success or failure in thus keeping away Chermes will 

 be most instructive. 



As to the practical treatment of infested trees little can be 

 done, at least when they are moderately large. 



On the Spruce the galls can be snipped off before they have 

 allowed the insects to escape in August ; but the remedy is a 

 troublesome one to adopt. They should be carefully burned 

 after gathering. If trees, especially avenue or ornamental trees, 

 are laden with galls, they had better be completely removed, 

 as the result will be serious stunting and deformity. 



The experiment of washing the Spruces in April before the 

 gall has grown would probably lead to good results, and this is 

 the best plan to adopt in the case of the Larch-aphis. 



The ordinary washes of kerosene (''paraffin oil") and soft- 

 soap are perhaps the most suitable, though they are not always 

 quite successful. The resin washes used in America are also 

 worthy of a trial. The formula is : — 



Eesin 20 lbs. 



Caustic soda (70 per cent.) 6 „ 



Fish oil 3 „ 



The ingredients are placed in a kettle, covered with water, and 

 boiled till saponified. Warm water is gradually added till the 

 mixture is made up to 100 gallons. Any common animal oil 

 can take the place of fish oil, and it will be seen that the 

 constituents are similar to those of common yellow soap with the 

 resin in excess. This is, in fact, what the wash is, and it can 

 probably be modified by using hard soap instead of oil, and 

 somewhat reducing the amount of caustic soda. 



Additions of tobacco-water, &c., to ordinary soft-soap wash 

 have been made and used, but are probably unnecessary. 

 Washes of dilute corrosive sublimate have also been tried with 

 some success, but no washes are proper to use against sucking 

 insects [AijMdes, &c.), unless they contain soap, oily matters, 



