442 



A.V ECOXOMIC EXTOMOLOGY. 



This is especially ettective in houses that are kept ven- warm and 

 moist. 



Standing on much the same plane is pyrethrum, or Persian 

 insect powder," or "buhach," which is a Californian product. 

 This is an exceedingly powerful contact poison, usually sold in 

 the form of a finely ground, yellowish powder, with a not un- 

 pleasant and somewhat pungent smell. Applied pure on most 

 insects of moderate size, and especially on lan'^, it quicklv 

 causes convulsions, and in most cases rapid death. It mav be 

 mixed with two or three times its own bulk of cheap hour, and if 

 the mixture is kept in tight jars for twenty-four hours, all parts 

 of it will be equally efiective. It is especially adapted for use 

 against plant-lice on a small scale, but is somewhat too expensive 

 for use in the field, or on a large scale. In small conservatories 

 nothing is better for general use. except against scale insects. 

 Where the dry powder is undesirable for any reason, use a de- 

 coction of an ounce in a gallon of water, first extracting with a 

 quart of boiling water and then adding cold water. Most naked 

 larv^ are rapidly afiected by this material : and while it is espe- 

 cially a contact poison, yet it is also fatal when eaten, except 

 in the case of large or adult insects. 



Among the contact poisons none ranks higher than kerosene, 

 either pure or made into an emulsion with soap. Pure kerosene 

 is fatal to almost aU insects : it is extremely penetrating, and 

 works its way through the spiracles into the body cavity and 

 through the trachea into all parts of it. This results in the prompt 

 choking of the insect. Pure kerosene is more or less injurious to 

 vegetation, although plants \-ary greatly in their resistance, and 

 it is therefore advisable to mix it with water, which can be ac- 

 complished by first emulsif\nng with either soap or milk. Prac- 

 tically, milk is rarely used at the present time, as the soap 

 formula is less expensive and. in general, more efiective. The 

 following is the method of preparing the emulsion : 



Hard soap, shaved fine one-half pound. 



Water i gallon. 



Kerosene 2 gallons. 



Dissolve the soap in boiling water, warm the kerosene and add 

 the boiling hot suds to it ; then churn with a force-pump for a 



