Acute, Lethal and Synergistic Effects of Some Terpenes Against Tribolium castaneum Herbst (Coleoptera: Tenebrionidae)

Terpenes are found in abundance in all plant essential oils. In the present study two pure volatile compounds of terpene group, α-pinene and β-caryophyllene have been evaluated for their repellent, acute toxicity and developmental inhibitory activities alone and in binary combination against red flour beetle Tribolium castaneum. In repellency assay, α-pinene and β-caryophyllene repelled T. castaneum adults significantly even at 0.025% concentrations. Fumigation of larvae and adults of T. castaneum with these two compounds caused lethality in them. Median lethal concentrations (LC50) of α-pinene and β-caryophyllene against adults were 0.998 and 1.624 μl/cm3 and against larvae were 1.379 and 1.949 μl/cm3 respectively. In binary combination, the LC50 values against adults and larvae were found 1.277 and 1.438 μl/cm3 respectively. Fumigation with two sublethal concentrations viz. 40 and 80% of 24-h LC50 of these two compunds alone and in binary combination significantly reduced oviposition potential of adults and inhibited pupation and adult emergence in larvae. All the responses were found concentration-dependent. From the present study, it can be concluded that α-pinene is more active than β-caryophyllene and these two volatile compounds in binary combination shows synergism and thus, can used as efficient insecticidal tool against T. castaneum as fumigant either alone or in combination.