(R)-(-)-Linalool was identified as a minor component sex pheromone of the scarab beetleHolotrichia parallela (Coleoptera: Scarabaeidae). Field evaluations revealed that, although not attractive per se, (R)-(-)-linalool enhances the attractiveness of the major sex pheromone,L-isoleucine methyl ester (LIME). Analyses of the pheromone titers in the glands of field-collected females demonstrated the occurrence of peak levels of 48-hr ("circabidian") periodicity. The levels of LIME in the glands of 45-day-old virgin females increased over three times from the scototo the photophase of a calling day, but the amounts of (R)-(-)-linalool did not significantly change. Virgin females had in average two times more LIME and 3.6 times more (R)-(-)-linalool than the average amount found in the field-captured beetles throughout the season.