L. Parra, A. Mutis, F. Ortega, and A. Quiroz. 2013. Field response of Hylastinus obscurus Marsham (Coleoptera: Curculionidae) to ,E-2-hexenal and limonene, two host-derived semiochemicals. Cien. Inv. Agr. 40(3): 637-642. Red clover (Trifolium pratense L.), a valuable legume in Chile, is important mainly for seed production and as forage for animal production. Although it is considered a perennial, the productivity of this legume declines during the second year of growth primarily because of infestation by the red clover root borer, Hylastinus obscurus (Coleoptera: Curculionidae). Currently, there is no efficient method for controlling this insect, although the use of semiochemicals may provide a new alternative to reduce the damage caused by this curculionid. In this context, E-2-hexenal and limonene, which were previously determined to be an attractant and a repellent, respectively, for H. obscurus, were released from dispensers established in two cultivars (Quiñequeli INIA and Superqueli INIA) and one experimental line (Syn II Pre III) of red clover at the Centro Regional de Investigación Carillanca (INIA-Carillanca) (Vilcún, Chile). H. obscurus was found in significantly higher numbers on plants from areas treated with E-2-hexenal than from areas treated with limonene or in areas that were left untreated as control areas. However, this attractiveness was influenced by the red clover source such that the effect of E-2-hexenal was observed in Superqueli INIA and Syn II Pre III but not in Quiñequeli INIA. Unlike previous studies, limonene had no effect on H. obscurus. Our results provide the first evidence under field conditions for the potential use of E-2-hexenal as an attractant for the red clover root borer H. obscurus.