REMEDIES AGAINST FOREST INSECTS. 37 



force-pump and spray-nozzle for five miuutes. The emulsion, if per- 

 fect, forms a cream wiiich thickens on cooling and should adhere with- 

 out oiliness to the surface of glass. Dilute, before using, one part of 

 the emulsion with nine parts of cold water. The above formula makes 

 3 gallons of emulsion, and when diluted gives 30 gallons of wash. 



Resin Washes. — Various compounds of resin and emulsions of resin 

 with kerosene are now being extensively used in California against scale- 

 insects and other enemies of the orange tree. Resin compounds were 

 first used as an insecticide by one of my agents, Mr. Albert Koebele, 

 and his experiments with this substance are given in full in my annual 

 reports as United States Entomologist for 1886 and 1887, and addi- 

 tional experiments by Mr. Coquillett are given in the report for 1888. 



Mr. Koebele had good success with the resin compound prepared as 

 follows : Dissolve 3 pounds of sal-soda and 4 pounds of resin in 3 pints 

 of water above tire ; when properly dissolved, add water slowly, while 

 boiling, to make 36 pints of compound. A very strong solution of this 

 was used on pear tiees without injury to the foliage, the solution con- 

 sisting of 3 pints of the compound to 4 of water. Numerous successful 

 experiments were made with one part of the compound and 8 parts of 

 water, and this strength for most purposes will be sufficient. 



Mr. Coquillett has found the following to be an excellent formula for 



the preparation of this compound:* 



Caustic soda pound.. 1 



Resiu ^ pounds . . 8 



Water to make gallons.. 32 



Dissolve by boiling the caustic soda in a gallon of ivater ; add the resin to one half 

 the soda solution and dissolve it by boiling ; add the remainder of the soda solution 

 and boil over a hot fire, stirring constantly. When sufficiently cooked it will assim- 

 ilate with water like milk, which it much resembles. Add water and strain through 

 a fine sieve. 



An emulsion of kerosene with resiu compound was satisfactorily ac- 

 complished by taking equal parts of both substances and working them 

 together for two minutes with a pump. This emulsion is not so stable 

 as the emulsion with soap, but is eminently effective against scale- 

 insects and Aphides. At my suggestion the addition of arsenic in the 

 proportion of 1 pound to from 75 to 300 gallons of the resin, or resin 

 and kerosene wash, was made, and this addition was found to greatly 

 increase the efficiency of these insecticides. 



The value of these insecticides for the protection of shade and orna- 

 mental trees, which, where scale-insects abound, are as liable to attack 

 and injury as the various fruit trees, need not here be emphasized. 



FuMiGANTS — Gases. — The destruction of hot-house pests by fumiga- 

 tion with sulphur, tobacco, or other noxious substances has long been 

 practiced. The application of such methods to trees on a large scale is, 

 however, of recent origin. 



The experiments of the last few years conducted by my California 

 agent, Mr. D. W. Coquillett, relating to the use of poisonous fumes or 

 gases against the scale insects of citrous trees have been attended with 

 *See Rep. of the U. S. Entomologist for 1888, p. 130. 



