Terpenes associated with resistance against the gall wasp, Leptocybe invasa, in Eucalyptus grandis

Abstract

Leptocybe invasa is an insect pest causing gall formation on oviposited shoot tips and leaves of Eucalyptus trees leading to leaf deformation, stunting, and death in severe cases. We previously observed different constitutive and induced terpenes, plant specialized metabolites that may act as attractants or repellents to insects, in a resistant and susceptible clone of Eucalyptus challenged with L. invasa. We tested the hypothesis that specific terpenes are associated with pest resistance in a Eucalyptus grandis half-sib population. Insect damage was scored over 2 infestation cycles, and leaves were harvested for near-infrared reflectance (NIR) and terpene measurements. We used Bayesian model averaging for terpene selection and obtained partial least squares NIR models to predict terpene content and L. invasa infestation damage. In our optimal model, 29% of the phenotypic variation could be explained by 7 terpenes, and the monoterpene combination, limonene, α-terpineol, and 1,8-cineole, could be predicted with an NIR prediction ability of .67. Bayesian model averaging supported α-pinene, γ-terpinene, and iso-pinocarveol as important for predicting L. invasa infestation. Susceptibility was associated with increased γ-terpinene and α-pinene, which may act as a pest attractant, whereas reduced susceptibility was associated with iso-pinocarveol, which may act to recruit parasitoids or have direct toxic effects.

Predicting terpene content in dried conifer shoots using near infrared spectroscopy

“…r 2 of cross-validation for α-pinene = 0.24, concentration range ca. 0–15 mg g −1 ) 18 . These studies suggest it should be possible to improve the precision of the existing calibrations by adding samples with a wider range of terpene concentration.…”

“…100 g of dried, ground plant sample), 13 a luxury not always available in experimental studies. A few studies correlated the spectra of dried leaves to oil-based laboratory analyses with success, notably with aromatic herbs 13,17 and Eucalyptus trees, 18 and this procedure has yet to be tested for conifer trees (but see Ercioglu et al. 13 for coniferous shrubs).…”

Terpenes and Terpenoids in Plants: Interactions with Environment and Insects

“…It was reported that the extent of damage caused by these larvae is commensurate to the upregulation of the biosynthesis of the VOC blend [ 75 , 76 ]. Iso-pinocarveol is proposed to potentially act as a recruiter of parasitoids in addition to having toxic properties [ 86 ] ( Table 2 ).…”

“…This strategy could be particularly useful or practical in mitigating and managing the agricultural and economic impacts of these unwanted insect pests. A study [ 86 ] has demonstrated an important association between increased γ-terpinene and α-pinene production in Eucalyptus grandis and its subsequent susceptibility to pest infestation, indicating the potential utility of these terpenes as attractants to E. grandis pest Leptocybe invasa , or a potential decoy/trap when expressed in non-host plant species.…”

The Road to Resistance in Forest Trees

“…Metabolomics in forest tree-biotic stress interactions have been limited to the study of specific secondary metabolites, e.g. terpenes (Oates et al., 2015; Naidoo et al., 2018), using methods such gas or liquid chromatography coupled to mass spectrometry (GC-MS and LC-MS, respectively) and near-infrared reflectance (NIR) technologies. Metabolomics in European common ash, Fraxinus excelsior , revealed different profiles associated with resistance and tolerance to the fungus, Hymenoscyphus fraxineus (Sambles et al., 2017).…”