THE TOXICITIES OF THREE PETROLEUM OILS TO THE GRAIN WEEVILS

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Abstract
The toxicities of three petroleum oils to Calandra granaria L. and C. oryzae L. have been determined. The oils were Shell oil P31, Odourless Distillate (O.D.), and Pool burning oil (P.B.O.). At 20 and 25° C. C. oryzae was more resistant than C. granaria to a direct spray of P31. At 20° C. C. oryzae was more resistant than C. granaria to direct sprays of O.D. and P.B.O. The relative toxicities to both species of direct sprays of the three oils could be expressed as: P.B.O. < P31 ≥ O.D. ≥ P.B.O. C. oryzae was the species more resistant to films of P31 on Whatman no. 544 filter‐paper.Films of P31 or a P31/water emulsion on brick, and films of P31 on sacking and cement, were non‐toxic to C. granaria, but films of P31 on cement pretreated with gelatin were highly toxic to this species.Beetles that received doses of P31 a little in excess of those sufficient to knock them down rarely recovered completely. P31 probably suffocates the beetles by blocking their spiracles and/or tracheae.P31 appears to be the most useful of the three oils for the control of C. granaria. In practice it should be effective as a direct spray, though not as a film, and could therefore be used to control infestations in which beetles were exposed. Films of P31 on surfaces suitably pretreated might, however, be used for control.