Abstract
In large parts of Europe, insecticide-free measures for protecting conifer plants are desired to suppress damage by the pine weevil Hylobius abietis (L.). Treatment with methyl jasmonate (MeJA), a chemical elicitor already used in crop production, may enhance expression of chemical defenses in seedlings in conifer regenerations. However, in a previous experiment, MeJA treatment resulted in substantially better field protection for Scots pine (Pinus sylvestris L.) than for Norway spruce (Picea abies (L.) Karst.). Hypothesizing that the variations may be at least due partly to volatiles released by MeJA-treated seedlings and their effects on pine weevil orientation, we examined tissue extracts of seedlings (from the same batches as previously used) by two-dimensional GC-MS. We found that the MeJA treatment increased contents of the monoterpene (−)-β-pinene in phloem (the weevil’s main target tissue) of both tree species, however, the (−)-β-pinene/(−)-α-pinene ratio increased more in the phloem of P. sylvestris. We also tested the attractiveness of individual monoterpenes found in conifer tissues (needles and phloem) for pine weevils using an arena with traps baited with single-substance dispensers and pine twigs. Trap catches were reduced when the pine material was combined with a dispenser releasing (−)-β-pinene, (+)-3-carene, (−)-bornyl acetate or 1,8-cineole. However, (−)-α-pinene did not have this effect. Thus, the greater field protection of MeJA-treated P. sylvestris seedlings may be due to the selective induction of increases in contents of the deterrent (−)-β-pinene, in contrast to strong increases in both non-deterrent (−)-α-pinene and the deterrent (−)-β-pinene in P. abies seedlings.Electronic supplementary materialThe online version of this article (doi:10.1007/s10886-016-0790-z) contains supplementary material, which is available to authorized users.
Highlights
The pine weevil [Hylobius abietis (L.)] is a major forest pest in Europe and Asia as it feeds on the bark of newly planted conifer seedlings, and may kill up to 90 % of seedlings at some sites without protective measures (Petersson and Orlander 2003)
Monoterpenes dominated the volatile fraction of the tissues of both species, and generally were more abundant in P. abies than in P. sylvestris
Changes in volatile terpene contents of tissues of P. sylvestris and P. abies seedlings induced by methyl jasmonate (MeJA) treatment may affect their attractiveness to pine weevils
Summary
The pine weevil [Hylobius abietis (L.)] is a major forest pest in Europe and Asia as it feeds on the bark of newly planted conifer seedlings, and may kill up to 90 % of seedlings at some sites without protective measures (Petersson and Orlander 2003). Methyl jasmonate elicitation influences the plants’ metabolism (Reymond and Farmer 1998), inter alia triggering the production of terpene and phenolic defenses (Fäldt et al 2003; Huber et al 2005; Keeling and Bohlmann 2006; Martin et al 2002). It induces formation of traumatic resin ducts and polyphenolic parenchyma cells (Hudgins et al 2004). Because of their potential applications in pest control, physiological and chemical responses to MeJA have been widely studied in both conifer seedlings (Fäldt et al 2003; Gould et al 2008; Heijari et al 2005; Moreira et al 2009, 2012; Pham et al 2014; Zeneli et al 2006) and trees (Erbilgin et al 2006; Fäldt et al 2003; Schiebe et al 2012; Zhao et al 2011)
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