Constitutive and herbivore‐induced monoterpenes emitted by Populus × euroamericana leaves are key volatiles that orient Chrysomela populi beetles

Abstract

Chrysomela populi beetles feed on poplar leaves and extensively damage plantations. We investigated whether olfactory cues orientate landing and feeding. Young, unexpanded leaves of hybrid poplar emit constitutively a blend of monoterpenes, primarily (E)-b-ocimene and linalool. This blend attracts inexperienced adults of C. populi that were not previously fed with poplar leaves. In mature leaves constitutively emitting isoprene, insect attack induces biosynthesis and emission of the same blend of monoterpenes, but in larger amount than in young leaves. The olfactometric test indicates that inexperienced beetles are more attracted by adult than by young attacked leaves, suggesting that attraction by induced monoterpenes is dose dependent. The blend does not attract adults that previously fed on poplar leaves. Insect-induced emission of monoterpenes peaks 4 d after the attack, and is also detected in nonattacked leaves. Induced monoterpene emission is associated in mature leaves with a larger decrease of isoprene emission. The reduction of isoprene emission is faster than photosynthesis reduction in attacked leaves, and also occurs in non-attacked leaves. Insect-induced monoterpenes are quickly and completely labelled by 13 C. It is speculated that photosynthetic carbon preferentially allocated to constitutive isoprene in healthy leaves is in part diverted to induced monoterpenes after the insect attack.

<sup>13</sup>C labelling study of constitutive and stress-induced terpenoide missions from Norway spruce and Scots pine

“…This conclusion agrees with other studies on stress-induced emissions (Loughrin et al, 1994;Pare and Tumlinson, 1997;Martin et al, 2003;Brilli et al, 2009) wherein it is shown that insect induced terpenoid emissions as well as induced emissions from the shikimate pathway are mainly de novo emissions. In contrast, the constitutive monoterpene 20 emissions from both conifers had much lower de novo fractions (Table 3) with values quite consistent to the empirical light dependent factor (LDF) given by Guenther et al (2012) with values ranging from 0.05 to 0.1 for most monoterpenes.…”

The impact of bark beetle infestations on monoterpene emissions and secondary organic aerosol formation in western North America

“…These studies include both beetle infestation studies and fungal inoculation studies and have found significant increases in monoterpenes due to beetle attack (e.g. Gara et al, 1993;Litvak and Monson, 1998;Jost et al, 2008;Amin et al, 2012;Prieme et al, 2000;Blande et al, 2007;Brilli et al, 2009). Insect herbivory can induce both substantial increases in total monoterpene emissions from vegetation and changes in the emission profile, with implications for atmospheric composition.…”

“…Although numerous studies have demonstrated that the VOC increase occurs in many plant species caused by many insect species (e.g. Blande et Brilli et al, 2009;Staudt and Lhoutellier, 2007), differences between the pine and spruce scale-up factors indicate that different tree species may have very different responses to bark beetle attacks. We include these two scenarios here in an effort to characterize this range of responses.…”

Attractiveness of Constitutive and Herbivore-Induced Sesquiterpene Blends of Maize to the Parasitic Wasp Cotesia marginiventris (Cresson)

“…For example, undamaged poplars (Populus spp.) can invest more than 10% of their photosynthetically fixed carbon into the emission of isoprene (Brilli et al, 2009). The majority of studies on vegetative VOCs have focused on herbivoreinduced volatiles and provided ample evidence for their role in attraction of herbivore enemies.…”