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THE need for economy in the use of pyrethrum extracts in insecticidal practice makes necessary the continuous search for substitute toxic agents or at least for activator substances which may be added to pyrethrin mixtures as adjuvants to raise their effectiveness and thus cut down the consumption of pyrethrin. Parkin1 published in NATURE the description of a method of biological assay of pyrethrin sprays in which the test insects (Tribolium castaneum), bred and kept under rigidly controlled conditions, are exposed by means of a standard method of application to various concentrations of pyrethrum extract in heavy oil. This method yields a reliable discrimination between the toxic effect of two solutions differing by 0-1 percent in their content of pyrethrin I, which amounts roughly to a difference of 0.2 per cent in their total pyrethrin content. According to Parkin, careful organization of a steady supply of insects from controlled stocks is one of the factors essential for the practical success of this method of assay.

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  1. 1

    Parkin, E. A., NATURE, 149, 720 (1942).

  2. 2

    Pumphrey, R. J., and Rawdon-Smith, A. F., Proc. Roy. Soc., B, 122, 106 (1937).

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