Repellency of rosemary oil and its components against the onion aphid, Neotoxoptera formosana (Takahashi) (Homoptera, Aphididae)

Olfactory behaviors of Neotoxoptera formosana, an aphid pest of allium crops, to host and non-host plant odors were investigated with a linear track olfactometer. Aphids were significantly attracted to odors of host plants, Allium fistulosum and A. tuberosum. On the contrary, they were repelled by odors of non-host plants, rosemary and pennyroyal. The odor of pennyroyal masked the attractiveness of host plant odor and the odor of rosemary repelled aphids even in the presence of host plant odor. Rosemary oil also had a repellency effect against aphids, and repelled them even in the presence of host plant odor. Six components of rosemary oil identified by GC-MS analysis, 1,8-cineole, d,l-camphor, alpha-pinene, etc., showed this repellency as well. 1,8-Cineole and d,l-camphor repelled aphids even in the presence of host plant odor and alpha-pinene masked host plant attractancy. 1,8-Cineole is the main component of rosemary oil and is thought to be main factor responsible for the repellency of rosemary. It was concluded that N. formosana may use host plant odors for host selection and be repelled by certain non-host plant odors. Rosemary volatiles may play an important role in defense of the plants from attack by parasites.