Location: Pest Management ResearchTitle: Dock leaf beetle, Gastrophysa viridula Deg., herbivory on Mossy Sorrel, Rumex confertus Willd: Induced plant volatiles and beetle orientation responses) Author
Submitted to: Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2011
Publication Date: 1/1/2012
Publication URL: http://handle.nal.usda.gov/10113/55029
Citation: Piesik, D., Wenda-Piesik, A., Ligor, M., Buszewski, B., Delaney, K.J. 2012. Dock leaf beetle, Gastrophysa viridula Deg., herbivory on Mossy Sorrel, Rumex confertus Willd: Induced plant volatiles and beetle orientation responses. Journal of Agricultural Science. 4(1): 97-103. 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 dock leaf 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 the top biological control candidate, the dock leaf beetle. Mossy sorrel plants receiving beetle feeding had much higher levels of three green leaf volatiles (GLVs, commonly emitted after leaf injury to plants) and three terpenes (usually specific to biotic injury (herbivores & pathogens). Subsequent tests with the beetles showed that both sexes were attracted to a concentration similar to induced levels for two common GLVs, but none of the terpenes. At the highest dose tested (much higher than emitted concentrations measured), the dock beetles were repelled by the two GLVs and two of the 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 mossy sorrel volatile results and the dock leaf beetle attraction/repulsion dose responses closely matching results with a closely related biological control beetle. These results reinforce the possibility that potential biological control agents use VOCs from a target weed host plant as information about host quality and whether to attack injured plants. This information is useful to consider how successful such a biological control insect might be to controlling a target invasive weed.
Technical Abstract: The invasive weed Rumex confertus Willd. (mossy sorrel) is fed upon and severely defoliated by Gastrophysa viridula Deg. (dock leaf beetle), a highly promising biological control agent for this weed. We report volatile organic compound (VOC) induction when one leaf on R. confertus was damaged by G. viridula adults to better understand plant responses to herbivory. A Y-tube bioassay was used to evaluate upwind orientation of adult G. viridula to single VOCs to examine initial beetle attraction or repellence to plant VOCs induced by herbivory from conspecifics. The R. confertus volatile blend induced by G. viridula feeding included three green leaf volatiles (GLVs; (Z)-3-hexenal, (Z)-3-hexen-1-ol, (Z)-3-hexen-1-yl acetate) and three terpenes (linalool, ß-caryophyllene, ß-farnesene). Overall, R. confertus that had been damaged by G. viridula released far greater concentrations of these six VOCs than control plants that were uninjured, and control plants did not release significantly detectable (from 0 ng) amounts of some VOCs. Male and female G. viridula had no significant attraction or repulsion to (Z)-3-hexen-1-ol or ß-caryophyllene. A significantly greater proportion of female and male beetles were attracted to (Z)-3-hexenal (5 ng'min-1 = 300 ng'hr-1) and (Z)-3-hexen-1-yl acetate (5 and 25 ng'min-1), in the range of induced concentrations emitted by a single injured leaf. The highest concentration of these two GLVs (125 ng'min-1) and the terpenes linalool and ß-farnesene significantly repelled females and males (or they avoided those VOCs). Our results found the same induced R. confertus VOCs to G. viridula feeding as from that of a congener G. polygoni (except (Z)-3-hexen-1-ol for the latter), and attraction/repulsion dose responses of both beetle species were very similar. The orientation responses of both Gastrophysa spp. will need to be tested will the full VOC bouquet induced by herbivory, and blends of only subsets of those induced VOCs.