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Title: Gastrophysa polygoni herbivory on Rumex confertus: Single leaf VOC induction and dose dependent herbivore attraction/repellence to individual compounds

item PIESEK, DARIUSZ - University Of Technology And Life Sciences
item WENDA-PIESEK, ANNA - University Of Technology And Life Sciences
item KOTWICA, KAROL - University Of Technology And Life Sciences
item LYSZCZARZ, ALICJA - University Of Technology And Life Sciences
item Delaney, Kevin

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2011
Publication Date: 10/7/2011
Citation: Piesek, D., Wenda-Piesek, A., Kotwica, K., Lyszczarz, A., Delaney, K.J. 2011. Gastrophysa polygoni herbivory on Rumex confertus: Single leaf VOC induction and dose dependent herbivore attraction/repellence to individual compounds. Journal of Plant Physiology. 168(17): 2134-2138.

Interpretive Summary: Some plants are invasive weedy species because of high levels of seed production that allows for rapid spread. One example of this is mossy sorrel, also called Asiatic dock weed that rapidly invades habitats and affects cattle forage (quantity and quality) in Europe. As a result, biological control of mossy sorrel is being considered with beetles that specialize on the genus of plants containing dock and sorrel weeds. Here, we measured concentrations of emitted mossy sorrel volatile organic compounds (VOCs) after a leaf was fed upon by one of the candidate biological control agent beetles. Mossy sorrel plants receiving feeding injury had much higher levels of two green leaf volatiles (GLVs, commonly emitted after leaf injury to plants) and three terpenes (usually specific to herbivory or pathogen infection injuties). Subsequent tests with the beetles showed that both sexes were attached to a concentration similar to induced levels for the two GLVs, for none of the three terpenes. At the highest dose tested (much higher than emitted concentrations measured), the dock beetles were repelled by both GLVs and one of the three terpenes. Our results suggest that in the field that low levels of dock beetle feeding might attract more beetles to mossy sorrel as a target weed host plant, while large amounts of feeding might repel beetles from coming to a highly injured plant; these will have to be confirmed with field tests. Our results could suggest that potential biological control agents use VOCs from a target weed host plant as information about host quality, and perhaps whether to attack plants with different levels of herbivory injury. This might have an influence on how successful such a biological control insect would be with a target weed host.

Technical Abstract: We report large induction (> 65fold increases) of volatile organic compounds (VOCs) emitted from a single leaf of the invasive weed mossy sorrel, Rumex confertus Willd. (Polygonaceae), by herbivory of the dock leaf beetle, Gastrophysa polygoni L. (Coleoptera: Chrysomelidae). The R. confertus VOC blend induced by G. polygoni herbivory included two green leaf volatiles ((Z)-3-hexenal, (Z)-3-hexen-1-yl acetate) and three terpenes (linalool, ß-caryophyllene, (E)-ß-farnesene). Uninjured leaves produced small constitutive amounts of the GLVs and barely detectable amounts of the terpenes. A Y-tube olfactometer bioassay revealed that both sexes of adult G. polygoni were attracted to (Z)-3-hexenal and (Z)-3-hexen-1-yl acetate at a concentration of 300 ng•h-1. No significant G. polygoni attraction or repellance was detected for any VOC at other concentrations (60 and 1500 ng•h-1). Yet, G. polygoni males and females were significantly repelled by (or avoided) at the highest test concentration (7500 ng•hr-1) of both GLVs and (E)-ß-farnesene. Mated male and female G. polygoni might be attracted to injured R. confertus leaves, but might avoid R. confertus when VOC concentrations (especially the terpene (E)-ß-farnesene) suggest high overall plant injury from conspecifics, G. viridula, or high infestations of other herbivores that release (E)-ß-farnesene (e.g., aphids). Tests in the future will need to examine G. polygoni responses to VOCs emitted directly from uninjured (constitutive) and injured (induced) R. confertus, and examine whether R. confertus VOC induction concentrations increase with greater tissue removal on a single leaf and/or the number of leaves with feeding injury.