Inducibility of chemical defences by two chewing insect herbivores in pine trees is specific to targeted plant tissue, particular herbivore and defensive trait

Abstract

There is increasing evidence that plants can react to biotic aggressions with highly specific responses. However, few studies have attempted to jointly investigate whether the induction of plant defences is specific to a targeted plant tissue, plant species, herbivore identity, and defensive trait. Here we studied those factors contributing to the specificity of induced defensive responses in two economically important pine species against two chewing insect pest herbivores. Juvenile trees of Pinus pinaster and P. radiata were exposed to herbivory by two major pest threats, the large pine weevil Hylobius abietis (a bark-feeder) and the pine processionary caterpillar Thaumetopoea pityocampa (a folivore). We quantified in two tissues (stem and needles) the constitutive (control plants) and herbivore-induced concentrations of total polyphenolics, volatile and non-volatile resin, as well as the profile of mono- and sesquiterpenes. Stem chewing by the pine weevil increased concentrations of non-volatile resin, volatile monoterpenes, and (marginally) polyphenolics in stem tissues. Weevil feeding also increased the concentration of non-volatile resin and decreased polyphenolics in the needle tissues. Folivory by the caterpillar had no major effects on needle defensive chemistry, but a strong increase in the concentration of polyphenolics in the stem. Interestingly, we found similar patterns for all these above-reported effects in both pine species. These results offer convincing evidence that induced defences are highly specific and may vary depending on the targeted plant tissue, the insect herbivore causing the damage and the considered defensive compound.

Tougher and thornier: general patterns in the induction of physical defence traits

“…; Moreira et al . ). A consequence of the discovery that herbivore elicitors drive plant chemical induction has been a shift in the experimental methodology of these studies to exclude ‘herbivory’ treatments that involve only mechanical damage to simulate herbivory.…”

“…; Moreira et al . ). In contrast, almost nothing is known about specificity in the induction of physical defence traits, and many studies simulate herbivory using artificial damage without the application of herbivore elicitors or jasmonates (Gibson, Bazely & Shore ; Abdala‐Roberts & Parra‐Tabla ; Valkama et al .…”

Herbivore specificity and the chemical basis of plant–plant communication in Baccharis salicifolia (Asteraceae)

“…Our results showed that there is herbivore specificity of plant–plant communication, because herbivore resistance on receiver Baccharis salicifolia plants increased only when emitter and receiver plants were attacked by the same aphid species. Specificity of induced defences against herbivores has been found across several plant–herbivore systems (Agrawal, ; Bingham & Agrawal, ; Xiao et al ., ; Moreira et al ., , ; Rowen & Kaplan, ). Such specificity could have evolved by means of natural selection, and may thus be adaptive (Bingham & Agrawal, ).…”

Methyl Jasmonate-Induced Monoterpenes in Scots Pine and Norway Spruce Tissues Affect Pine Weevil Orientation

“…Both P. sylvestris and P. abies responses to MeJA included accumulation of ( − )-β-pinene in phloem, a stress response observed in several conifer species to various treatments (Gould et al 2009; Moreira et al 2013; Persson 2003; Sampedro et al 2010). In P. abies , ( − )-α-pinene was induced at the same time as ( − )-β-pinene, possibly due to activation of ( − )α/β-pinene synthase (Martin et al 2004).…”