"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 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." (Himanen et al. 2010:722)