Behavioral responses for evaluating the attractiveness of specific tea shoot volatiles to the tea green leafhopper, Empoaca vitis

The tea green leafhopper, Empoasca vitis Gothe, is one of the most serious insect pests of tea plantations in mainland China. Over the past decades, this pest has been controlled mainly by spraying pesticides. Insecticide applications not only have become less effective in controlling damage, but even more seriously, have caused high levels of toxic residues in teas, which ultimately threatens human health. Therefore, we should seek a safer biological control approach. In the present study, key components of tea shoot volatiles were identified and behaviorally tested as potential leafhopper attractants. The following 13 volatile compounds were identified from aeration samples of tea shoots using gas chromatography-mass spectrometry (GC-MS): (E)-2-hexenal, (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, 2-ethyl-1-hexanol, (E)-ocimene, linalool, nonanol, (Z)-butanoic acid, 3-hexenyl ester, decanal, tetradecane, beta-caryophyllene, geraniol and hexadecane. In Y-tube olfactometer tests, the following individual compounds were identified: (E)-2-hexenal, (E)-ocimene, (Z)-3-hexenyl acetate and linalool, as well as two synthetic mixtures (called blend 1 and blend 2) elicited significant taxis, with blend 2 being the most attractive. Blend 1 included linalool, (Z)-3-hexen-1-ol and (E)-2-hexenal at a 1 : 1 : 1 ratio, whereas blend 2 was a mixture of eight compounds at the same loading ratio: (E)-2-hexenal, (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, 2-penten-1-ol, (E)-2-pentenal, pentanol, hexanol and 1-penten-3-ol. In tea fields, the bud-green sticky board traps baited with blend 2, (E)-2-hexenal or hexane captured adults and nymphs of the leafhoppers, with blend 2 being the most attractive, followed by (E)-2-hexenal and hexane. Placing sticky traps baited with blend 2 or (E)-2-hexenal in the tea fields significantly reduced leafhopper populations. Our results indicate that the bud-green sticky traps baited with tea shoot volatiles can provide a new tool for monitoring and managing the tea leafhopper.