Synthetic Cis-Jasmone Exposure Induces Wheat and Barley Volatiles that Repel the Pest Cereal Leaf Beetle, Oulema melanopus L.

The plant semiochemical cis-jasmone primes/induces plant resistance that deters herbivores and attracts natural enemies. We studied the induction of volatile organic compounds (VOCs) in winter wheat and spring barley after exposure of plants to three synthetic cis-jasmone doses (50 μl of 1, 100, and 1?×?10⁴ ng μl^?1) and durations of exposure (1, 3, and 6 h). Cereal leaf beetle, Oulema melanopus, adult behavioral responses were examined in a Y-tube olfactometer to cis-jasmone induced plant VOC bouquets and to two synthetic blends of VOCs (3 green leaf volatiles (GLVs); 4 terpenes?+?indole). In both cereals, eight VOCs (Z)-3-hexanal, (Z)-3-hexanol, (Z)-3-hexanyl acetate, (Z)-β-ocimene, linalool, β-caryophyllene, (E)-ß–farnesene, and indole] were induced 100- to 1000-fold after cis-jasmone exposure. The degree of induction in both cereals was usually positively and linearly associated with increasing exposure dose and duration. However, VOC emission rate was only ~2-fold greater from plants exposed to the highest vs. lowest cis-jasmone exposure doses (1?×?10⁴ difference) or durations (6-fold difference). Male and female O. melanopus were deterred by both cereal VOC bouquets after plant exposure to the high cis-jasmone dose (1?×?10⁴ ng μl^?1), while females were also deterred after plant exposure to the low dose (1 ng μl^?1) but attracted to unexposed plant VOC bouquets. Both O. melanopus sexes were repelled by terpene/indole and GLV blends at two concentrations (25 ng?·?min^?1; 125 ng?·?min^?1), but attracted to the lowest dose (1 ng?·?min^?1) of a GLV blend. It is possible that the biologically relevant low cis-jasmone dose has ecological activity and potential for inducing field crop VOCs to deter O. melanopus.