FIELD BOOK OF INSECTS, 



are also effective against such leaf-chewing insects as have 

 thin skins. A corrosive insecticide which is strong enough 

 to kill an insect having a thick skin will kill the leaves also. 

 Scale insects, except when young and scaleless, will resist 

 any insecticide that leaves resist. Therefore, strong 

 solutions (such as lime-sulphur) must be used on them 

 before the buds break. Some contact insecticides work 

 by clogging up the insects' breathing apparatus (tracheae) 

 rather than by corrosion. All contact insecticides should 

 be applied, if possible, directly on the insect. It is usually 

 a waste to spray them on leaves that are not affected. 



Kerosene is very effective and may be applied pure 

 about chicken houses and against bedbugs, but not on 

 plants. For plants, an emulsion is used which can be 

 purchased or may be made as follows: "Dissolve }4. 

 pound of hard or whale-oil soap (or I quart soft soap) in 

 i gallon of boiling water. Add 2 gallons of kerosene and 

 churn with a force pump by pumping back and forth for 

 five to ten minutes until the oil is thoroughly emulsified, 

 forming a creamy mass with no drops of free oil visible. 

 This stock solution is now diluted so that the resulting 

 mixture will contain the desired per cent of kerosene. 

 Thus for aphids one part of the stock solution should be 

 diluted with from 10 to 15 parts of water, giving from 4 to 

 6 per cent of kerosene in the spray, while for a winter wash 

 for San Jose scale, it should be diluted only three or four 

 times giving from 1 6 to 22 per cent kerosene. The emul- 

 sion must be thoroughly churned and should be applied 

 with a nozzle throwing a fine spray" (Sanderson). 



Ordinary laundry soap, one-half pound to a gallon of 

 water, is a good insecticide. Whale-oil soap is, perhaps, a 

 little better. There are many brands of miscible oil 

 which are very good. Lime-sulphur wash is used chiefly 

 against the San Jose scale and is rather difficult to make at 

 home. Pure sulphur dust is effective against "red spider. " 



Pyrethrum, or Persian insect powder, is much used 

 about houses as it is not poisonous and does not injure 

 fabrics, but it deteriorates with age. It works by suffo- 

 cating the insect. 



A tobacco tea made by boiling or steeping a pound of 

 tobacco leaves and stems in one or two gallons of water is 



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