Better Effect of a Lower Dose of Plant Substances in Deterring Storage Pests

The aim of the study was to compare the effect of two concentrations (0.1 and 1%) of different plant substances on dettering Rhyzopertha dominica F. and Sitophilus granarius L. Both species were treated with the essential oils of Foeniculum vulgare Mill. and Carum carvi L. as well as L-carvone, anethole and thymoquinone. In addition, the repellent effect of yachycline oil and dialyl disulphide was tested on R. dominica. The tests were carried in laboratory. The deterrence of insects were noted after 1, 2, 3, 4, 5, 24 and 48 h. It turned out that the essential oils and chemical compounds used in the experiments do not show the normal relationship described in the previous literature on storage pests, in which the repellency gets higher with the increase in the concentration of the tested plant material. It was found that a lower dose of the tested substances causes a greater deterrence of these species of beetles. In the case of R. dominica, the highest repellant effect was exerted by the concentration of 0.1%: carvone, diallyl disulphide and yachlane oil. Differences between the concentration of 0.1% and 1% were found among all tested substances in each time interval in the deterrent of R. dominica. This difference ranged from 4.17% to 52.92%. All substances used in the tests had a large deterrent effect on S. granarius (from 48 to 100%). Differences in the deterrence of S. granarius were found between 0.1% and 1% concentration in most of the tested substances in each time interval. The difference ranged from 1% to 15.42%.