Promising bioinsecticidal effect of Tunisian Anethum graveolens L. (dill) (Umbelliferae) essential oil against confused flour beetle, Tribolium confusum Jaquelin du Val. 1863 (Coleoptera: Tenebrionidae)

This report focused on the repellency and lethal effects of Anethum graveolens essential oils (EO) on the confused flour beetle Tribolium confusum (Coleoptera: Tenebrionidae). The active substances of obtained Anethum EO, polysaccharides and extracts (decoction and maceration) were identified by the FTIR spectrum. Bioactive components of Anethum extract obtained by maceration were evaluated by the HPLC apparatus. Repellency and mortality experiments were carried out by using two concentrations of the volatile oil at different time points. Chemical analysis of extracts and EO from genus Anethum showed that aromatic and phenolics were the main constituents. Anethum essence depicted dose-dependent repellency effects. It is worth noting that the larvae and adult insects showed repellency index values of 0.38 and 0.44, respectively, after treatment with dill low dose. Accordingly, the repellent index of the essential oil at two concentrations of 3.44 and 8.92 mu l/cm(2) (0.0 < RI <= 0.44) indicates that the repellency effect for both ages is similar. The findings of the lethality experiment showed that the LT of the essential oil on T. confusum was 3.21 days. It induced the high rate of lethality with LT50 of T. confusum at 2.8 and 9 mu l/cm(2) concentrations was 2.63 and 1.13, respectively, and the highest repellent potency with RC50 of 1.38 +/- 6.12 %. The experiment findings indicated that the mortality rate of the adult and larvae of the grain borer T. confusum is a concentration of essential oil and exposure period-dependent manner when compared to untreated control. Further, A. graveolens was found to kill 76.1 +/- 5.2 % larvae and 74.3 +/- 10.1 % adult insects at 24 h. The LD50 of Anethum essence was 1.23 mu l/cm(2) for larvae and 2.14 mu L/cm(2) for adults. This value was markedly (P <0.05) higher on larvae than on adults. These findings proved that the essence of Anethum seeds is promising bioactive phytocompounds of botanical insecticides towards the stored product insects.