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Clover root borer Hylastinus obscurus (Marsham) (Coleoptera: Scolytidae) has no preference for volatiles from root extracts of disease infected red clover

Red clover, Trifolium pratense L., is an important forage legume grown in North America and Europe. Soil-climatic conditions in southern Chile are also favourable for the establishment of red clover stands. Although red clover is considered a perennial plant, red clover stands often decline to unsatisfactory levels within two years after sowing (Cuevas & Balocchi, 1983; Leath, 1985; Steiner & Alderman, 2003). Factors that may contribute to reduced persistence of red clover include root rot severity, and root borer Hylastinus obscurus (Marsham) infestations (Graham & Newton, 1959; Carrillo & Mundaca, 1974). At present there is no control for clover root borers other than rotation (Aguilera et al., 1996). A few studies have been carried out on the chemical interrelationship between the rootrot complex of red clover with borers feeding on clover roots. Leath and Byers (1973) reported that in preference tests performed in Petri dish chambers adult borers were more attracted to water-leached materials from diseased red clover roots than to leached materials from healthy roots. Some volatile compounds identified in a hexane extract of diseased red clover roots were also found attractive to borers in Petri dish preference tests, but in field tests no individual compound or mixture was attractive to adult borers (Kamm & Buttery, 1984). As the authors in the preceding behavioural studies used still-air bioassays, the present study attempted to determine whether adult borers could discern between odours released from ethanolic extracts of healthy and disease-infected red clover roots by using a four-arm olfactometer, a more powerful statistical design (Hare, 2000) that utilizes moving air.