Lethal and sublethal effects of essential oils of Ajwain (Carum copticum L.) and fennel (Foeniculum vulgare Mill) along with diatomaceous earth on some life table parameters of the lesser grain borer (Rhyzopertha dominica F.)

The lesser grain borer, Rhyzopertha dominica F. is an important pest of the stored products, which causes severe economic damage on grain. Regarding necesity of using alternative methods to chemical insecticides, in the present study the lethal and sublethal effects of the essential oils of Ajwain (Carum copticum L.) and fennel (Foeniculum vulgare Mill) along with diatomaceous earth were evaluated against R. dominica. The chemical compositions of the essential oils were determined by gas chromatography-mass spectrometry. The major components of Ajwain were phenol, benzene, and γ-terpinene and those of the fennel were propanal, trans-anethole, γ-terpinene, benzene, and cyclohexene. The toxicity of fennel essential oil (LC50 = 103.83 µl/l air) against the adults of R. dominica was higher than Ajwain essential oil (LC50 = 167.46 µl/l air). The LC50 for the diatomaceous earth was obtained 0.052 g/kg. Results of the experiment of sublethal effects (LC30) showed that males and females’ longevity and the fecundity of females were significantly lowest in the combination of Ajwain essential oil along with diatomaceous earth. Furthermore, the net reproductive rate (R0), intrinsic rate of natural increase (rm), and finite rate of increase (λ) of the pest, in both the combination of Ajwain essential oil along with diatomaceous earth and fennel essential oil along with diatomaceous earth were significantly lower (P < 0.05) than other treatments. The results of this study indicated that the essential oils of each of these plants in combination with diatomaceous earth can be used in the management programs of R. dominica.