394 ECONOMIC ENTOMOLOGY 



infested with weevils and other insects. It is also used for the de- 

 struction of household pests such as clothes moths, etc. 



Two pounds of the liquid is sufficient for loo bu. of peas or 

 grain, or looo cu. ft. of space. It is inflammable. 



(b) Hydrocyanic Acid Gas. — This gas is liberated when diluted 

 sulphuric acid is added to potassium or sodium cyanide. It is a deadly 

 poisonous gas, and great care should be taken in its use as an insecticide. 



It came into use in California for the fumigation of citrus and oHve 

 trees. Later it was introduced into eastern nurseries for the treatment 

 of San Jose scale on dormant nursery stock, and for the control of 

 flour mill pests, and, in some cases, greenhouse and household pests. 



The formula for nursery stock and household fumigation is: Cya- 

 nide of potash or soda, i oz.; sulphuric acid (sp. gr., 1.83), i fl. oz.; 

 water, 3 fl. oz. per 100 cu. ft. space. For greenhouse fumigation at 

 night the formula is: Cyanide of potash or soda, ^ oz.; sulphuric acid, 

 I fl. oz.; water, 3 fl. oz. per 1000 cu. ft. space. 



This gas is lighter than air and diffuses very rapidly. 



(c) Sulphur Fumes. — The destructive action of sulphur is largely 

 due to the readiness with which it oxidizes to sulphur dioxide, a gas 

 fatal to many forms of insect life. Mites are controlled in green- 

 houses by the dusting of fine sulphur on the surfaces of the leaves. 



When sulphur is burned on a hot plate over a low flame sulphur 

 dioxide is rapidly formed, recognized by its suffocating odor. This 

 is, perhaps, the simplest method of dealing with ordinary household 

 pests such as bed bugs, fleas, and other forms. 



Combined with a soap, sulphur is used as a wash for mange which 

 is caused by a mite. 



(d) Tobacco. — Tobacco fumes are destructive to aphids on green- 

 house and household plants. They are liberated by the application 

 of heat to certain Nicotine Extracts, Nicotine Paper, or finely divided 

 tobacco powders. These "fumigating" powders and extracts may 

 now be had in the market and are convenient methods of dealing 

 with house plants. 



(e) Formalin. — As a rule, formalin (40 per cent, formaldehyde) is 

 not effective as an insecticide, although an excellent germicide. As a 

 fly-poison, however, it is strongly recommended when used as follows: 

 Mix I tablespoonful formalin with } 2 cup sweet milk or }^ cup water, 

 and expose in a shallow plate with a slice of bread in it. 



