Sources of Insect and Plant Volatiles Attractive to Cottonwood Leaf Beetles Feeding on Hybrid Poplar

Abstract

The cottonwood leaf beetle, Chrysomela scripta, is the most damaging insect affecting the production of Populus, an important source of sustainable forest products and biomass. Currently, there is no simple method for monitoring C. scripta populations, and nothing is known about potential chemical attractants for trapping. We conducted laboratory assays on sources of attraction to C. scripta adults. In olfactometer trials, beetles were attracted to volatiles released from conspecifics feeding on foliage. There was also significant, but lesser, attraction to odor from unwounded foliage, C. scripta alone, and frass. The latter two results indicate the presence of a pheromone. Wounding of foliage by C. scripta, but not by artificial means, enhanced its attractiveness compared to unwounded foliage, even when C. scripta by-products were removed. In direct comparisons, responses to odor from beetle-wounded foliage were not different from responses to odor from beetles feeding on foliage. We tested the attractiveness of volatiles emitted by adults feeding on foliage in the field using modified boll weevil traps. Results confirm that these volatiles are sufficient to increase trap catches in the field. Color is also important, with yellow baited traps catching more beetles than black baited. We propose that original landing by C. scripta is mediated by host odors and visual cues and that subsequent aggregation is enhanced by chemical cues associated with feeding by conspecifics. This may partially explain clustering in the field and likewise be incorporated into sampling schemes needed for integrated pest management.