The persistent Toxicity under standardised field Conditions of Pyrethrum, DDT and “Gammexane” against Pests of stored Food

Abstract

The persistent toxicity of films of pyrethrum in P31 oil may endure on suitable surfaces under warehouse conditions for much longer periods than hitherto supposed, but unexplained fluctuations in toxicity may occur.Within the range 0·8 per cent. to 1·3 per cent. total pyrethrins, the pyrethrum content appears to be only a minor factor in determining the persistent toxicity of such films.The nature of the surface sprayed is of great importance in determining the persistent toxicity of pyrethrum films in P31 oil, which is negligible on concrete and increases steadily through the following list of surfaces—brick, heavy hessian, light hessian, jute, cotton, and wood; the last-mentioned two being particularly good substrates.Residual deposits of DDT or “ Gammexane ” derived from kerosene sprays are of little use on concrete, but appear otherwise little affected by the nature of the surface treated; they give a uniform degree of persistent toxicity on the various surfaces listed.