50 APPLIED ENTOMOLOGY 



giving a Stock Solution in which the oil, broken up into very tiny droplets, 

 will not run together again and the water can dilute the mixture. For use 

 against soft-bodied insects, 1 part of the Stock Solution is mixed with 

 about 9 parts of water to spray, while for tougher insects, 1 part is diluted 

 with 4 or 5 parts of water, though this strength may sometimes injure 

 the plants somewhat. The Stock Solution, if well prepared, should keep 

 before breaking down (shown by a film of oil appearing on the surface) 

 for at least a month or two. If the materials fail to thicken in the pump 

 it is probably because the water is "hard water." In that case add a 

 little borax or soda to soften it. 



Crude Petroleum can be used in place of kerosene in preparing this 

 emulsion, provided the right grade can be obtained, but this is often 

 difficult, and so is not frequently done. 



Miscible Oils. — These are stronger than kerosene emulsion. They 

 contain mineral oils, a small amount of vegetable oil, naphthaline in 

 some cases, some alkali, and water. Properly made they dilute readily 

 with water. 



A number of brands of miscible oils are on the market, prepared 

 mainly as sprays for the control of scale insects. For winter use against 

 scales they are generally diluted at the rate of 1 part of the oil to 12 

 to 14 parts of water. When used in summer against plant lice the dilu- 

 tion should be about 1 part to 35 to 40 parts of water. 



The material should not be used if free oil stands on it, as this shows 

 that it has broken down and is not safe on the plants. If sprayed on trees 

 in freezing weather it may gather and freeze in cracks of the trees, in- 

 juring them. It is easy to handle and spreads readily from where it 

 strikes, covering more than would otherwise be the case, but it has been 

 claimed, with considerable evidence to support it, that repeated treat- 

 ments with miscible oils cause a cumulative injurious effect on trees. 



Among soaps, common laundry soap and whale-oil (generally fish-oil 

 now) soap are the usual materials used as insecticides. 



Whale-oil Soap. — This is a soap made by combining fish oil with an 

 alkali, preferably potash. It is usually diluted at the rate of 1 lb. to 5 

 or 6 gal. of water to apply against plant lice and similar soft-bodied 

 insects in summer, but is also a fair winter application for scale insects, 

 at the rate of 2 lb. per gallon of water, though more costly than other, 

 equally good materials. 



Common Soap. — This is a fairly good material at the rate of 1 lb. in 

 3 to 5 gal. of water for summer use against plant lice and other soft- 

 bodied ir^sects but is not as effective as whale-oil soap and is mentioned 

 only because the latter cannot always be obtained. 



Nicotine. — This is an alkaloid which occurs in tobacco. It can be 

 obtained by soaking tobacco stems in warm water till a dark brown liquid 

 containing nicotine is obtained, and this is of some value as an insecticide. 



