76 INSECTICIDES FOR SUCKING INSECTS 
tions range from 1 part to 500 in the case of resistant insects down 
to 1 part to 1000 in the case of tender plant lice. The dilutions for 
killing lice and mites on animals are similar to the last named. The 
strength of 1 to 500 should be used only as a wash and not as a dip, 
when treating pests on animals. 
“Sulphate of Nicotine” is a preparation of similar strength, and 
the dilutions are the same. 
Liquid “ Nico-Fume ” contains 40 per cent free nicotine, but the 
dilutions and manner of use are similar to the above. 
“ Black Leaf Extract’ contains a much lower percentage of nico- 
tine, and less water is added to it than to the others named. 
Home-made Tobacco Extract 
If tobacco stems or tobacco dust are available, an extract may be 
made at home. To prepare, pack the stems in a pail or kettle and 
cover with water. Allow to stand over night. Or, boil 1 pound of 
dust or stems in 1 gallon of water. An hour’s boiling is sufficient. 
Dilute the extract with 1 to 2 parts of water. This material 
may safely be applied to plants in leaf and is effective against plant 
lice. Add soap at the rate of 1 pound to 50 gallons of spray. It is 
not advisable to employ this as a winter spray to kill the eggs of plant 
lice because the percentage of nicotine present may not be sufficient. 
Insect Powder 
Insect powder : , : : : . 1 ounce 
Water . : : : : : : ; . 2 gallons 
This is the material variously known as pyrethrum, buhach, or 
Persian insect powder. It consists of the finely ground flower buds 
of a plant. The active principle is volatile ; hence the material rapidly 
loses its strength on exposure to air. It must be fresh, or must have 
been kept in a closed receptacle, to be effective. 
Commonly it is used dry. Small powder guns are obtainable for 
applying it. 
To use it as a spray, mix 1 ounce in 2 gallons of water. If it is 
