Root Volatile Components of Red Clover: Identification and Bioassay with the Clover Root Borer (Coleoptera: Scolytidae)1

Abstract

Extracts from diseased red clover roots ( Trifolium pratense L.) were fractionated and bioassayed for attractiveness to the clover root borer ( Hylastinus obscurus Marsham). Twenty volatile components were identified in fractions attractive to the borer using Tenax trapping and direct solvent extraction. These and previously identified foliar compounds were bioassayed in the laboratory for attractiveness to the borer. Of 21 foliar compounds, only methyl salicylate evoked a positive response. Of 15 root compounds, 10 were attractive to the borer. None of the attractive compounds was competitive with crude extracts of diseased roots when tested individually. Certain combinations of ethyl laurate, ethyl benzoate, methyl salicylate, eugenol, hexadecanal, and chavicol were competitive with crude extracts of diseased root in laboratory tests. Adult borers were not attracted to individual compounds or mixtures in preliminary field tests.