EXTRACTS FROM CORRESPONDENCE. 
WATER-PROOF INSECTICIDES. 
For vears I have been investigating the habits of insects injurious to 
fruit and vegetables. I find that all insects are more or less suscepti- 
ble to smells, and their depredations can be largely prevented by the use 
of some pungent odor. The cureulio (Conotrachelus nenuphar), for exam- 
ple, can be almost entirely driven from plum-trees by the oil of penny- 
royal mixed with lard and rubbed on the branches, or cotton wool satu- 
rated with the same and suspended in muslin bags throughout the 
tree as soon as the first blossoms begin to open. I have never known 
this to fail, if done in season and thoroughly and at once renewed in 
case of rain. I have also used to advantage a strong decoction of quas- 
sia against the rose-bugs (Macrodactylus subspinosus). I have made-va- 
rious successful experiments in this line. I think I have made a faith- 
ful test of all the well-known insecticides, and am fully satisfied that 
when decoctions, tinctures, or emulsions are used, or when the poison 
can be temporarily held in suspension, the finer the spray the more effi- 
cacious appears the remedy. I think there can be no question on this 
point. <A single trial of the tincture of pyrethrum will be sufficient to 
prove this statement. How far pyrethrum can take the place of Paris 
green or London purple may still be an open question, or whether re- 
fined coal-oil mixed with milk or other ingredients will supply the use 
of these poisons and be equally effectual without the consequent danger. 
In the use of the various liquid insecticides in my experiments I 
found that their effects were often entirely nullified by exposure to the 
air, or the material itself was washed off by the first rain. This led me 
to experiment how to avoid this trouble.- An addition of glue and bi- 
chromate of potash proved the best remedy. I use from one to two 
ounces of glue and one-quarter ounce of the bichromate to a gallon of 
the liquid. The glue should be soaked twenty-four hours in cold water; 
then dissolved in hot water. The two are to be thoroughly mixed with 
the liquid insecticide. The application should in every case be made in 
the form of a minute spray. After the evaporation of the moisture, 
which takes place in a few minutes, there remains an almost water- 
proof residuum retaining all its virtues. I believe I have given these 
experiments a most thorough trial, and that the result has been all that 
could be desired. There are other chemicals which will produce similar 
results, but, as far as my experience goes, the above has proved the 
best. 
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