PLANT ANIMAL INTERACTIONS Elena Valkama Æ Julia Koricheva Æ Vladimir Ossipov Svetlana Ossipova Æ Erkki Haukioja Æ Kalevi Pihlaja Delayed induced responses of birch glandular trichomes and leaf surface lipophilic compounds to mechanical defoliation and simulated winter browsing Received: 12 November 2004 / Accepted: 12 July 2005 / Published online: 27 September 2005 Ó Springer-Verlag 2005 Abstract Changes in morphology and chemistry of leaf surface in response to herbivore damage may increase plant resistance to subsequent herbivore attack; however, there is lack of studies on induced responses of glandular trichomes and their exudates in woody plants and on effects of these changes on herbivores. We studied de- layed induced responses in leaf surface traits of five clones of silver birch (Betula pendula Roth) subjected to various types of mechanical defoliation and simulated winter browsing. Glandular trichome density and concentrations of the majority of surface lipophilic compounds increased in trees defoliated during the pre- vious summer. This induced response was systemic, since control branches in branch defoliated trees responded to the treatments similarly to defoliated branches, but dif- ferently from control trees. In contrast to defoliation treatments, simulated winter browsing reduced glandular trichome density on the following summer and had fewer effects on individual surface lipophilic compounds. Moreover, constitutive density of glandular trichomes was negatively correlated with induced total amount of lipophilic compounds per trichome, indicating a trade- off between constitutive and induced resistance in silver birch. Induced changes in leaf surface traits had no sig- nificant effect on leaf damage by chewers, miners and gall mites, but increased susceptibility of birch trees to aphids. However, leaf damage by chewers, miners and gall mites in defoliated (but not in control) trees was correlated with concentrations of some fatty acids and triterpenoids, although the direction of relationships varied among herbivore species. This indicates that induction of surface lipophilic compounds may influence birch resistance to herbivores. Our study thus demon- strated both specificity of elicitation of induced responses of birch leaf surface traits by different types of damage and specificity of the effects of these responses on dif- ferent types of herbivores. Keywords Betula pendula Æ Genotype Æ Induced susceptibility Æ Induced resistance Æ Plant–insect interaction Æ Trade-offs Introduction Plant resistance to herbivores can be divided into a constitutive component, which is always expressed in the plants and functions independently of damage, and an inducible component, which refers to changes in plants following damage (Karban and Baldwin 1997). Induced responses to herbivore damage have been reported for many plant families and include changes in plant chemical composition, phenology, morphology, photo- synthesis and growth (reviewed by Karban and Baldwin 1997). Some of these changes may occur immediately after damage and affect the same herbivores that have inflicted the damage (rapid induced responses) whereas other responses may take longer to develop and manifest themselves in the seasons after damage (delayed induced responses). The latter type of response is characteristic of mechanical defences such as trichomes, spines and thorns, because their production cannot be induced in mature tissues and requires new growth for its expres- Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/ 10.1007/s00442-005-0216-z and is accessible for authorized users. Communicated by Christian Koerner E. Valkama (&) Æ J. Koricheva Æ E. Haukioja Section of Ecology, Department of Biology, University of Turku, 20014 Turku, Finland E-mail: elekos@utu.fi Tel.: +358-2-3335722 Fax: +358-2-3336550 V. Ossipov Æ S. Ossipova Æ K. Pihlaja Laboratory of Environmental Chemistry, Department of Chemistry, University of Turku, 20014 Turku, Finland J. Koricheva Present address: School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, TW20 0EX UK Oecologia (2005) 146: 385–393 DOI 10.1007/s00442-005-0216-z