REMEDIES AGAINST FOREST INSECTS. 37 
force-pump and spray-nozzle for five minutes. The emulsion, if per- 
fect, forms a cream which 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 fire ; 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 water ; 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 fiue sieve. 
An emulsion of kerosene with resin 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 resiu 
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 1838, p. 130. 
