Abstract: Coccinella septempunctata, from Coccinellidae family of Coleoptera, is a natural predator of aphids, whitefly, and other major agricultural pests and thus plays an important role in biological control of these pests. In this study, we identified the volatile components (VOCs) of the Chinese herbal plant of snake-bed grass Cnidium monnieri infested by the aphid Semiaphis heraclei using dynamic head-space adsorption and gas chromatography-mass spectrometry (GC-MS). The behavioral response of C. septempunctata to the snake-bed grass after aphid infestation and six kinds of VOCs differentially released by the plants were observed by Y-tube olfactometer, in order to explore the role of these VOCs in attracting predator C. septempunctata. The results showed that: (1) Compared with the control, C. septempunctata adults preferred healthy and aphid-infested plants, but there was no significant difference in attracting C. septempunctata adults between the healthy plants and those infested by aphids. (2) A total of 33 kinds of VOCs were all detected in the healthy plants, infested plants with and without S. heraclei aphids after the infestation, which were classified into eight classes: alkanes, alkenes, aromatic hydrocarbons, alcohols, esters, ketones, aldehydes, and phenols. (3) Aphid infestation significantly enhanced the relative contents of n-heptane, n-undecane, n-dodecane, p-xylene, 2-ethylhexanol and p-ethylacetophenone, and reduced the relative contents of tetradecane, heptadecane, α-pinene, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate and 4-ethylbenzaldehyde in the VOCs from C. monnieri plants with and without aphids after the infestation. (4) 10 μL·mL^-1 p-xylene exhibited a significant attraction to both male and female adults of C. septempunctata, with the selection rate of 76.7% and 73.3% respectively. 10 μL·mL^-1 p-ethylacetophenone had a significant attraction to male adults of C. septempunctata with a selection rate of 70.0%. Our results indicated that p-xylene, n-heptane, and p-ethylacetophenone in the VOCs from C. monnieri can be used to make the attractants for C. septempunctata in fields to improve the biocontrol effect of natural enemies.

Key words: Cnidium monnieri, Semiaphis heraclei, Coccinella septempunctata, plant volatile, behavioral response, biocontrol