Paropsis atomaria larval feeding induces a chemical but not a physical response in Corymbia citriodora subsp. variegata

Key message Corymbia citriodora subsp. variegata altered the expression of secondary metabolites in response to Paropsis atomaria larval feeding and mechanical wounding but did not alter leaf toughness and leaf trichomes. Plants have evolved strategies against herbivore pressure, relying on constitutive or induced traits that create physical and chemical barriers, which may influence herbivore performance. We evaluated the physical and chemical responses of Corymbia citriodora subsp. variegata, an important hardwood plantation taxon, to feedings by Paropsis atomaria larvae, a pest that causes severe defoliation in young trees. This was undertaken to obtain insights into plant-herbivore interactions, aiming to identify parameters that may improve plant fitness and/or protection that may benefit pest management in forestry plantations. Seedlings of C. citriodora subsp. variegata were submitted to the following treatments: no damage, mechanical wounding, and P. atomaria larval feeding damage. Foliar samples were collected during and after treatment at day 15 and 22, respectively, from damaged and undamaged leaves to detect: local, systemic, or delayed induced responses. Leaf samples were analysed to determine whether there were induced physical (leaf toughness, trichome density) or chemical (secondary metabolite profiles) responses to damage. No physical response in any of the treatments was evident in C. citriodora subsp. variegata foliage at day 15 or 22. Systemic chemical responses were observed for the larval feeding and mechanical treatments, with, a delayed response evident in the larval feeding treatment only. The proportion of long chain hydrocarbons were reduced in these treatments relative to the control, whereas the proportion of monounsaturated hydrocarbons and monoterpenes increased. When analysed across treatments, larval mortality was negatively correlated with long chain hydrocarbons and positively correlated with monounsaturated hydrocarbons. These findings suggest that CCV systemic chemical responses induced by both larval feeding and mechanical damage but only larval feeding induced delayed response, suggesting that CCV responses to herbivory may be associated with plant defence strategies.

Automated summary

The study found that Corymbia citriodora subsp. variegata exhibited systemic chemical responses when subjected to feeding by Paropsis atomaria larvae and mechanical damage, with a delayed response only observed in the larval feeding treatment. These findings suggest that the responses of CCV to herbivory may be associated with plant defense strategies.