Piperonyl Butoxide as a Constituent of Heavy-oil Sprays for the Control of Stored Product Insects. I.—Piperonyl Butoxide as a Synergist for Pyrethrum and its Effect on the Persistence of Pyrethrum Films

Laboratory experiments showed that piperonyl butoxide (PB) is a powerful synergist of pyrethrins in Shell oil P31. The toxicity of PB alone to different species of insects was determined. Tribolium castaneum was resistant to direct sprays of PB in P31, but appreciably susceptible to films : the toxic action of the films on this species was unusually delayed. Ptinus tedus and Calandragranaria were resistant to films, but C. oryzae somewhat susceptible. In view of claims that PB makes pyrethrum films more persistent, an experiment specifically designed to reveal such an effect was carried out. This failed to show that PB makes the films any more persistent. A formula was obtained giving the approximate pyrethrin equivalent of different pyrethrin-PB mixtures applied to T. castaneum as films on filter paper. It was shown, however, that the pyrethrin equivalent of a given pyrethrin-PB mixture could differ according to the method of application and according to the species of test insect.