EXTRACTS FROM CORRESPONDENCE. 



Water-proof Insecticides. 



For years 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 curculio ( Conotrachelus 7iennphar), 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 ho 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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