Birch (Betula spp.) leaves adsorb and re-release volatiles specific to neighbouring plants – a mechanism for associational herbivore resistance?

Authors

  • Sari J. Himanen,

    1. Department of Environmental Science, University of Eastern Finland, Kuopio Campus, PO Box 1627, FI-70211 Kuopio, Finland
    2. MTT Agrifood Research Finland, Plant Production Research, Lönnrotinkatu 5, FI-50100 Mikkeli, Finland
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  • James D. Blande,

    1. Department of Environmental Science, University of Eastern Finland, Kuopio Campus, PO Box 1627, FI-70211 Kuopio, Finland
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  • Tero Klemola,

    1. Section of Ecology, Department of Biology, University of Turku, FI-20014 Turku, Finland
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  • Juha Pulkkinen,

    1. Department of Biosciences, University of Eastern Finland, Kuopio Campus, PO Box 1627, FI-70211 Kuopio, Finland
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  • Juha Heijari,

    1. Department of Environmental Science, University of Eastern Finland, Kuopio Campus, PO Box 1627, FI-70211 Kuopio, Finland
    2. Kotka Maritime Research Centre, Mussalontie 428 B, FI-48310 Kotka, Finland
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  • Jarmo K. Holopainen

    1. Department of Environmental Science, University of Eastern Finland, Kuopio Campus, PO Box 1627, FI-70211 Kuopio, Finland
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Author for correspondence:
Sari J. Himanen
Tel. +358 40 738 9873
Email: Sari.Himanen@mtt.fi

Summary

  • Plant-emitted semi-volatile compounds have low vaporization rates at 20–25°C and may therefore persist on surfaces such as plant foliage. The passive adsorption of arthropod-repellent semi-volatiles to neighbouring foliage could convey associational resistance, whereby a plant’s neighbours reduce damage caused by herbivores.
  • We found that birch (Betula spp.) leaves adsorb and re-release the specific arthropod-repelling C15 semi-volatiles ledene, ledol and palustrol produced by Rhododendron tomentosum when grown in mixed association in a field setup. In a natural habitat, a higher concentration of ledene was released from birches neighbouring R. tomentosum than from birches situated > 5 m from R. tomentosum. Emission of α-humulene, a sesquiterpene synthesized by both Betula pendula and R. tomentosum, was also increased in R. tomentosum-neighbouring B. pendula.
  • In assessments for associational resistance, we found that the polyphagous green leaf weevils (Polydrusus flavipes) and autumnal moth (Epirrita autumnata) larvae both preferred B. pendula to R. tomentosum. P. flavipes also preferred birch leaves not exposed to R. tomentosum to leaves from mixed associations. In the field, a reduction in Euceraphis betulae aphid density occurred in mixed associations.
  • Our results suggest that plant/tree species may be protected by semi-volatile compounds emitted by a more herbivore-resistant heterospecific neighbour.

Ancillary