Comparing responses of generalist and specialist herbivores to various cyanogenic plant features

Authors

  • D. J. Ballhorn,

    Corresponding author
    1. Department of Plant Biology, University of Minnesota, 250 Biological Sciences Center, 1445 Gortner Avenue, St. Paul, MN 55108, USA
    2. Department of Botany/Plant Ecology, University of Duisburg-Essen, Universitätsstr. 5, 45117 Essen, Germany
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  • S. Kautz,

    1. Department of Botany/Plant Ecology, University of Duisburg-Essen, Universitätsstr. 5, 45117 Essen, Germany
    2. Department of Zoology, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL 60605, USA
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  • R. Lieberei

    1. Biocenter Klein Flottbek and Botanical Garden, University of Hamburg, Ohnhorststr. 18, 22609 Hamburg, Germany
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*D. J. Ballhorn, Department of Plant Biology, University of Minnesota, 250 Biological Sciences Center, 1445 Gortner Avenue, St. Paul, MN 55108, USA. E-mail: ballhorn@umn.edu, daniel.ballhorn@uni-due.de

Abstract

Plants are obliged to defend themselves against multiple generalist and specialist herbivores. Whereas plant cyanogenesis is considered an efficient defence against generalists, it is thought to affect specialists less. In the present study, we analysed the function of various cyanogenic features of lima bean [Phaseolus lunatus L. (Fabaceae)] during interaction with different herbivores. Three cyanogenic features were analysed, i.e., cyanogenic potential (HCNp; concentration of cyanogenic precursors), β-glucosidase activity, and cyanogenic capacity (HCNc; release of cyanide per unit time). In no-choice and free-choice feeding trials, five lima bean accessions were offered to generalist desert locust [Schistocerca gregaria Forskål (Orthoptera: Acrididae)] and specialist Mexican bean beetle [Epilachna varivestis Mulsant (Coleoptera: Coccinellidae)]. The HCNc was the most important parameter determining host plant selection by generalists, whereas choice behaviour of specialists was strongly affected by HCNp. Although locusts were effectively repelled by high HCNc, this cue was misleading for the detection of suitable host plants, as extensive consumption of low HCNc plant material resulted in strong intoxication of locusts. Balancing cyanide in consumed leaf area, the quantitative release of gaseous cyanide during feeding, and cyanide in faeces suggested that specialists metabolized significantly lower rates of cyanide per consumed leaf material than generalists. We hypothesize that specialists are able to avoid toxic concentrations of cyanide by using HCNp rather than HCNc as a cue for host plant quality, and that they exhibit mechanisms that reduce incorporation of host plant cyanide.

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