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White fringetree is a host for the invasive emerald ash borer (EAB) but is of lower quality than the related and highly susceptible black ash. Field observations suggest that host trees grown in full sun are more resistant to EAB than those in shade, however the impact of light limitation on chemical defenses has not been assessed. We quantified constitutive and jasmonate-induced phloem defenses and growth patterns of white fringetree and black ash under differential light conditions and related them to EAB larval performance. White fringetree had significantly lower constitutive and induced activities of peroxidase, polyphenol oxidase, β-glucosidase, chitinase and lignin content, but significantly higher gallic acid equivalent soluble phenolic, soluble sugar, and oleuropein concentrations compared to black ash. Multivariate analyses based on tissue chemical attributes displayed clear separation of species and induced defense responses. Further, EAB performed significantly worse on white fringetree than black ash, consistent with previous studies. Light limitation did not impact measured defenses or EAB larval performance, but it did decrease current year growth and increase photosynthetic efficiency. Overall our results suggest that phenolic profiles, metabolite abundance, and growth traits are important in mediating white fringetree resistance to EAB, and that short-term light limitation does not influence phloem chemistry or larval success. [ABSTRACT FROM AUTHOR]

Hemlock woolly adelgid is an invasive piercing-sucking insect in eastern North America, which upon infestation of its main host, eastern hemlock ('hemlock'), improves attraction and performance of folivorous insects on hemlock. This increased performance may be mediated by hemlock woolly adelgid feeding causing antagonism between the the jasmonic acid and other hormone pathways. In a common garden experiments using hemlock woolly adelgid infestation and induction with methyl jasmonate (MeJA) and measures of secondary metabolite contents and defense-associated enzyme activities, we explored the impact of hemlock woolly adelgid feeding on the local and systemic induction of jasmonic acid (JA)-elicited defenses. We found that in local tissue hemlock woolly adelgid or MeJA exposure resulted in unique induced phenotypes, whereas the combined treatment resulted in an induced phenotype that was a mixture of the two individual treatments. We also found that if the plant was infested with hemlock woolly adelgid, the systemic response of the plant was dominated by hemlock woolly adelgid, regardless of whether MeJA was applied. Interestingly, in the absence of hemlock woolly adelgid, hemlock plants had a very weak systemic response to MeJA. We conclude that hemlock woolly adelgid infestation prevents systemic induction of JA-elicited defenses. Taken together, compromised local JA-elicited defenses combined with weak systemic induction could be major contributors to increased folivore performance on hemlock woolly adelgid-infested hemlock. [ABSTRACT FROM AUTHOR]

Trees attacked by multiple herbivores need to defend themselves against dynamic biotic challenges; appropriate responses to one stressor can elicit hormonal responses that are antagonistic to another. Hemlock (Tsuga canadensis) infestation by hemlock woolly adelgid (HWA; Adelges tsugae) results in the accumulation of the defensive hormone salicylic acid.We explored the potential for HWA infestation to interfere with anti‐folivore‐induced defence signalling and its implications for a native folivore (hemlock looper; Lambdina fiscellaria). Hemlocks were infested with HWA and/or sprayed with methyl jasmonate; foliar defences were analyzed and foliage quality for looper larvae was assessed.Both treatments activated foliar defensive traits, including a HWA‐mediated increase in peroxidase activity and an accumulation of cell wall‐bound phenolics and lignin, as well as a methyl jasmonate‐mediated increase in lipoxygenase activity. The two treatments had an additive effect on other defensive traits and both treatments negatively affected looper performance.These results suggest that salicylic acid and jasmonic acid are not strictly antagonistic in conifers and that both have a role in anti‐folivore defence signalling. The present study illustrates the need for a better understanding of hormone signalling, cross‐talk and induced responses in conifers. [ABSTRACT FROM AUTHOR]