Identification of volatiles from differently aged red clover (Trifolium pratense) root extracts and behavioural responses of clover root borer (Hylastinus obscurus) (Marsham) (Coleoptera: Scolytidae) to them

Root extracts from 1.5 and 2.5-year-old red clover (Trifolium pratense) were obtained using supercritical fluid extraction (SFE). GC–MS analysis and Kovats indices allowed identification of the volatile compounds as butyl acetate, E-2-hexenal, α-pinene, benzaldehyde, 6-methyl-5-hepten-2-one, limonene, acetophenone, methyl benzoate, nonanal, octanoic acid and decanal.The extracts obtained and pure synthetic samples of the identified volatile components were tested in olfactometric bioassays with the insect Hylastinus obscurus (Coleoptera: Scolytidae). The results showed that the insect was attracted to root volatiles of 1.5-year-old extracts but not to those from 2.5-year-old extracts. A 10 μg dose of methyl benzoate and E-2-hexenal attracted the insect, whereas the same dose of limonene repelled the red clover borer. An increase in limonene content and a decrease in E-2-hexenal content were correlated with a loss of attraction to 2.5-year-old clover roots.