Proximate mechanisms of host plant location by a specialist phytophagous insect, the grape berry moth, Paralobesia viteana

Authors: WOLFIN, MICHAEL - Cornell University; CHILSON, RONALD - Cornell University; THRALL, JONATHAN - Hobart And William Smith Colleges; LIU, YUXI - Hobart And William Smith Colleges; VOLO, SARA - Hobart And William Smith Colleges; Cha, Dong; LOEB, GREGORY - Cornell University; LINN, CHARLES - Cornell University

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2019
Publication Date: 11/21/2019
Citation: Wolfin, M.S., Chilson, R.R., Thrall, J., Liu, Y., Volo, S., Cha, D.H., Loeb, G.M., Linn, C.E. 2019. Proximate mechanisms of olfactory mediated host plant location by a specialist phytophagous insect, the grape berry moth (Paralobesia viteana). Journal of Chemical Ecology. 45:946-958. https://doi.org/10.1007/s10886-019-01112-1.
DOI: https://doi.org/10.1007/s10886-019-01112-1

Interpretive Summary: Many herbivorous insects are believed to be more attracted to the odor (i.e. volatile chemicals) of their host plants than the odor of non-host plants for feeding and oviposition purposes. However, there are contrasting hypotheses regarding the mechanism for the host and non-host discrimination behavior. Researchers at the USDA-ARS laboratory in Hilo, HI and Cornell University in Geneva, NY tested this by evaluating attractiveness and volatile profiles of host plant (grape) and two non-host plants (apple and gray dogwood) for the grape berry moth (GBM), a native specialist moth pest of juice and wine grapes in the Eastern U.S. Contrary to our expectation, GBM females detected similar volatile chemicals from host and non-host plants and were equally attracted to host and non-host shoots, volatile extracts, and synthetic chemical blends in flight tunnel bioassays, suggesting that GBM may be using odor to locate favorable habitat rather than a specific host plant.

Technical Abstract: There are contrasting hypotheses regarding the mechanisms of host plant location, particularly regarding the role of plant volatiles. Here we use the grape berry moth (GBM; Paralobesia viteana)-grape plant (Vitis spp.) complex as a model for studying the proximate mechanisms of long distance olfactory mediated host plant location and selection by a specialist phytophagous insect. We used flight tunnel assays to observe GBM female in-flight responses to host (V. riparia) and non-host (apple, Malus domestica; and gray dogwood, Cornus racimosa,) odor sources in the form of plants, adsorbent extracts, and synthetic blends. Gas chromatography coupled with electroantennographic detection (GC-EAD) and GC-MS were used to identify the antenally active volatile compounds. All antenally active compounds found in grape shoots were also present in dogwood and apple shoots. Our original hypothesis was that if this specialist insect was using olfactory cues to discriminate host and non-host plants from a distance, then females would be sensitive to a specific mixture of host volatiles and also to specific non-host volatiles that could function as behavioral antagonists. However, female GBM flew upwind to host and non-host extracts and synthetic blends at similar levels, suggesting discrimination is not occurring at long distance from the plant. Further, whereas females did land on live plant sources in the tunnel they did not land on rubber septum sources releasing the volatile plant extracts and synthetic blends, suggesting not all landing cues were present in the extracts and volatile blends. Additionally, mated and unmated moths displayed similar levels of upwind flight responses to all odor sources, supporting the idea that plant volatiles are not functioning only as ovipositional cues. The results of this study, contrary to our original hypothesis for a specialist phytophagous insect, support the alternative hypothesis that these insects are using volatile blends to locate a favorable habitat rather than a specific host plant, and that discrimination is occurring within the habitat, or even post-landing.