Attractants for pest monitoring and controlling can be developed based on plant volatiles. Previously, we showed that tea leafhopper (Empoasca onukii) preferred grapevine, peach plant, and tea plant odours to clean air. In this research, we formulated three blends with similar attractiveness to leafhoppers as peach, grapevine, and tea plant volatiles; these blends were composed of (Z)-3-hexenyl acetate, (E)-ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene, benzaldehyde, and ethyl benzoate. Based on these five compounds, we developed two attractants, formula-P and formula-G. The specific component relative to tea plant volatiles in formula-P was benzaldehyde, and that in formula-G was ethyl benzoate. These two compounds played a role in attracting leafhoppers. In laboratory assays, the two attractants were more attractive than tea plant volatiles to the leafhoppers, and had a similar level of attractiveness. However, the leafhoppers were not attracted to formula-P in the field. A high concentration of benzaldehyde was detected in the background odour of the tea plantations. In laboratory tests, benzaldehyde at the field concentration was attractive to leafhoppers. Our results indicate that the field background odour can interfere with a point-releasing attractant when their components overlap, and that a successful attractant must differ from the field background odour.

Plant volatiles help herbivores to locate their hosts, and therefore, they could be used to help develop pesticide-free pest management strategies. To develop an attractant for tea leafhopper (Empoasca onukii), we screened nine tea plant volatile compounds for their attractiveness using Y-tube olfactometer assays. Results indicated that tea leafhoppers significantly preferred ocimene, limonene, (Z)-3-hexenol, and (Z)-3-hexenyl acetate over clean air. These compounds were combined in a blend which lost its attractiveness at concentrations below 10-2 g/ml in liquid paraffin. In field tests, the blend was attractive to leafhoppers only in autumn, but not in summer. Analyses of the tea field background odor showed that all four components of the blend were present at much higher concentrations in summer (0.05-0.001 ng/liter) than in autumn (~10- to 25-fold lower). In field Y-tube bioassays, compared with the tea field background odor, the blend was attractive at a concentration of 10-1 g/ml in liquid paraffin, but not at 10-2 g/ml. These results suggest that field background odor can disrupt the attractiveness of an attractant based on plant volatiles to herbivores.

The tea green leafhopper, Empoasca vitis (G€ othe) (Hemiptera: Cicadellidae), is a serious pest of tea plants. We examined the behavioral responses of E. vitis adults to odors from the shoots of three host plants in a Y-tube olfactometer with background visual cues. The host plants were tea [Camellia sinensis (L.) Kuntze (Theaceae)], peach [Prunus persica (L.) Siebold & Zucc. (Rosaceae)], and grapevine [Vitis vinifera L. (Vitaceae)]. Volatiles from the shoots were analyzed. Both yellow-green and gold backgrounds enhanced the olfactory responses of E. vitis adults to tea plant odors, and this enhancement was stronger under a high light intensity. On the yellow-green background, E. vitis adults significantly preferred the odors from shoots of the three host plants compared with clean air. Moreover, E. vitis adults preferred grapevine odor over the tea plant odor. The volatile blends of the three plant species were distinctly different. Peach plant shoots emitted the greatest amount of volatiles, whereas grapevine shoots released the greatest diversity of compounds. These results provide evidence that background visual cues could enhance the response of E. vitis adults to host-plant volatiles. The leafhoppers can discern different host odors, suggesting the possibility of using peach plant and grapevine odors to monitor and manage this pest in tea plantations.

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The lacewing Chrysopa phyllochroma Waesmael is a polyphagous predator of many pests. Releasing lacewings is an important component of biological control programs, but it is difficult to establish populations on field crops. Electrophysiological and behavioral responses to 10 common plant volatiles were recorded to screen for lacewing-attracting compounds. Electroantennographic assays indicated that all of the tested compounds elicited responses from C. phyllochroma. Three green-leaf volatiles-(E)-2-hexenal, (Z)-3-hexenyl acetate, and (Z)-3-hexenol-produced the strongest responses. Weaker responses were observed to six terpenes-ocimene, linalool, (3E)-4,8-dimethyl-1,3,7-nonatriene, (E,E)-α-farnesene, limonene, and nerolidol-and to methyl salicylate. Using a Y-tube olfactometer, the behavioral assays of the eight most active compounds demonstrated that four-(Z)-3-hexenyl acetate, (Z)-3-hexenol, (3E)-4,8-dimethyl-1,3,7-nonatriene, and linalool-were significant attractants for C. phyllochroma at specific concentrations. Three common plant volatile compounds-(Z)-3-hexenyl acetate, (3E)-4,8-dimethyl-1,3,7-nonatriene, and linalool-were also found to significantly enhance female ovipositing, resulting in a concentration of eggs. These observations are important for lacewing release as a pest control measure because they suggest means for retaining individuals and establishing populations using common plant volatiles.

Determination of volatile plant compounds in field ambient air is important to understand chemical communication between plants and insects and will aid the development of semiochemicals from plants for pest control. In this study, a thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method was developed to measure ultra-trace levels of volatile plant compounds in field ambient air. The desorption parameters of TD, including sorbent tube material, tube desorption temperature, desorption time, and cold trap temperature, were selected and optimized. In GC-MS analysis, the selected ion monitoring mode was used for enhanced sensitivity and selectivity. This method was sufficiently sensitive to detect part-per-trillion levels of volatile plant compounds in field ambient air. Laboratory and field evaluation revealed that the method presented high precision and accuracy. Field studies indicated that the background odor of tea plantations contained some common volatile plant compounds, such as (Z)-3-hexenol, methyl salicylate, and (E)-ocimene, at concentrations ranging from 1 to 3400 ng m(-3). In addition, the background odor in summer was more abundant in quality and quantity than in autumn. Relative to previous methods, the TD-GC-MS method is more sensitive, permitting accurate qualitative and quantitative measurements of volatile plant compounds in field ambient air.

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