A Preliminary Study of the Insecticidal Efficiency of the Pyrethrins, Nicotine and Rotenone Against the Greenhouse Red Spider Mite

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Abstract
Without the addition of some wetting agent, the pyrethrins, rotenone, and nicotine, even at high concentrations, have little toxicity to the greenhouse red spider mite. With the addition of 0.25 per cent potassium oleate soap, rotenone at 0.02 per cent is slightly more toxic than the pyrethrins (0.02 per cent); nicotine is much less toxic than either of these two, approximately 0.66 per cent being necessary to produce a mortality equivalent to that produced by the above concentrations of the other two poisons. With sulphonated castor oil as the wetting agent, the pyrethrins and rotenone at 0.02 per cent are about equivalent in toxicity; nicotine again is much less toxic, about 0.2 per cent being necessary to equal the insecticidal efficiency of the other two at the concentrations given above. Potassium oleate soap at 0.25 per cent and 0.5 per cent is approximately equivalent in toxicity to sulphonated castor oil at 0.5 per cent and 1 per cent, respectively. Soap is more efficient than sulphonated castor oil as a wetting agent for rotenone and the pyrethrins. With nicotine, however, the reverse appears to be true. Nicotine (1–500) makes distinctly alkaline the almost neutral 0.5 per cent sulphonated castor oil, but has a relatively slight effect on the already alkaline soap solution. Alcoholic extracts of the pyrethrins have an acidic effect when added to either sulphonated castor oil or soap solution. Acetone solutions of rotenone have very little effect on the pH of either of these wetting agents.

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