Temperate plants show a rapid seasonal turnover in various leaf traits and defenses. Such trends in plant defenses can potentially drive seasonal shifts in the specialization of insect herbivores. We quantified how non-volatile leaf metabolites, inducible volatile organic compounds (VOCs), C:N ratio and leaf toughness changed between the early, middle, and late seasons in five Salicaceae species and one Salix hybrid. We also explored seasonal trends in overall trait variation among the studied plants. We tested whether seasonal changes in dietary specialization of leaf-chewing larvae and adult beetles related to changes in the studied host-plant traits. Trait turnover occurred mainly through changes in VOCs and seasonal increase in traits that directly lower herbivore feeding efficiency. The overall variation in leaf traits was highest in the early season, with seasonal intraspecific variation being 33% smaller than the variation among species sampled at one time point. Although less frequently than we expected, the two groups of insect herbivores showed seasonal changes in specialization. The significant trends in herbivore specialization included peaks in the middle season for larval specialization based on VOCs and host phylogenetic relatedness and for adult beetle specialization based on C:N ratio plus leaf toughness. The detected species-specific trends in host-plant traits, their intraspecific variability, and differential trends among insect herbivores highlight the importance of considering seasonal variation when predicting trends in plant-herbivore interactions.

• Klíčová slova
• Chemical defenses, Leaf toughness, Salicinoids, Tannins, Volatile organic compounds,
• MeSH
• brouci fyziologie   MeSH
• býložravci * MeSH
• hmyz fyziologie   MeSH
• larva fyziologie   MeSH
• listy rostlin * MeSH
• roční období * MeSH
• Salicaceae * MeSH
• těkavé organické sloučeniny analýza   metabolismus   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• těkavé organické sloučeniny MeSH

Polyphagous insect herbivores feed on multiple host-plant species and face a highly variable chemical landscape. Comparative studies of polyphagous herbivore metabolism across a range of plants is an ideal approach for exploring how intra- and interspecific chemical variation shapes species interactions. We used polyphagous caterpillars of Lymantria mathura (Erebidae, Lepidoptera) to explore mechanisms that may contribute to its ability to feed on various hosts. We focused on intraspecific variation in polyphenol metabolism, the fates of individual polyphenols, and the role of previous feeding experience on polyphenol metabolism and leaf consumption. We collected the caterpillars from Acer amoenum (Sapindaceae), Carpinus cordata (Betulaceae), and Quercus crispula (Fagaceae). We first fed the larvae with the leaves of their original host and characterized the polyphenol profiles in leaves and frass. We then transferred a subset of larvae to a different host species and quantified how host shifting affected their leaf consumption and polyphenol metabolism. There was high intraspecific variation in frass composition, even among caterpillars fed with one host. While polyphenols had various fates when ingested by the caterpillars, most of them were passively excreted. When we transferred the caterpillars to a new host, their previous experience influenced how they metabolized polyphenols. The one-host larvae metabolized a larger quantity of ingested polyphenols than two-host caterpillars. Some of these metabolites could have been sequestered, others were probably activated in the gut. One-host caterpillars retained more of the ingested leaf biomass than transferred caterpillars. The pronounced intraspecific variation in polyphenol metabolism, an ability to excrete ingested metabolites and potential dietary habituation are factors that may contribute to the ability of L. mathura to feed across multiple hosts. Further comparative studies can help identify if these mechanisms are related to differential host-choice and response to host-plant traits in specialist and generalist insect herbivores.

• Klíčová slova
• chemical defenses, detoxification, flavonoids, frass, habituation, tannins,
• Publikační typ
• časopisecké články MeSH

Plants produce diverse chemical defenses with contrasting effects on different insect herbivores. Deploying herbivore-specific responses can help plants increase their defensive efficiency. Here, we explore how variation in induced plant responses correlates with herbivore species, order, feeding guild, and level of specialization. In a greenhouse experiment, we exposed 149 plants of Salix fragilis (Linnaeus, 1753) to 22 herbivore species naturally associated with this host. The insects belonged to four orders (Coleoptera, Lepidoptera, Hemiptera, and Hymenoptera), three feeding guilds (external leaf-chewers, leaf-tying chewers, and sap-sucking), and included both dietary specialists and generalists. Following herbivory, we quantified induced changes in volatiles and nonvolatile leaf metabolites. We performed multivariate analyses to assess the correlation between herbivore order, feeding guild, dietary specialization, chewing damage by herbivores, and induced responses. The volatile composition was best explained by chewing damage and insect order, with Coleoptera and Lepidoptera eliciting significantly different responses. Furthermore, we recorded significant differences in elicited volatiles among some species within the two orders. Variation in nonvolatile leaf metabolites was mainly explained by the presence of insects, as plants exposed to herbivores showed significantly different metabolites from controls. Herbivore order also played a role to some extent, with beetles eliciting different responses than other herbivores. The induction of volatile and nonvolatile leaf metabolites shows different levels of specificity. The specificity in volatiles could potentially serve as an important cue to specialized predators or parasitoids, increasing the efficacy of volatiles as indirect defenses. By contrast, the induction of nonvolatile leaf metabolites was largely unaffected by herbivore identity. Most nonvolatile metabolites were downregulated, possibly indicating that plants redirected their resources from leaves in response to herbivory. Our results demonstrate how diverse responses to herbivores can contribute to the diversity of plant defensive strategies.

• Klíčová slova
• Salix, chemical diversity, defense specificity, herbivory, induction, specialized metabolites, volatile organic compounds,
• Publikační typ
• časopisecké články MeSH

Induction of plant defences can show various levels of localization, which can optimize their efficiency. Locally induced responses may be particularly important in large plants, such as trees, that show high variability in traits and herbivory rates across their canopies. We studied the branch-localized induction of polyphenols, volatiles (VOCs), and changes in leaf protein content in Carpinus betulus L., Quercus robur L., and Tilia cordata L. in a common garden experiment. To induce the trees, we treated ten individuals per species on one branch with methyl jasmonate. Five other individuals per species served as controls. We measured the traits in the treated branches, in control branches on treated trees, and in control trees. Additionally, we ran predation assays and caterpillar food-choice trials to assess the effects of our treatment on other trophic levels. Induced VOCs included mainly mono- and sesquiterpenes. Their production was strongly localized to the treated branches in all three tree species studied. Treated trees showed more predation events than control trees. The polyphenol levels and total protein content showed a limited response to the treatment. Yet, winter moth caterpillars preferred leaves from control branches over leaves from treated branches within C. betulus individuals and leaves from control Q. robur individuals over leaves from treated Q. robur individuals. Our results suggest that there is a significant level of localization in induction of VOCs and probably also in unknown traits with direct effects on herbivores. Such localization allows trees to upregulate defences wherever and whenever they are needed.

• Klíčová slova
• Herbivory, Hornbeam, Indirect defences, Linden, Methyl jasmonate, Oak, Polyphenols, Protein content, Terpenes, VOCs,
• MeSH
• analýza hlavních komponent MeSH
• bukotvaré chemie   metabolismus   MeSH
• býložravci * MeSH
• hmyz MeSH
• obranné mechanismy proti býložravcům * MeSH
• stromy chemie   metabolismus   MeSH
• těkavé organické sloučeniny analýza   metabolismus   MeSH
• Tilia chemie   metabolismus   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• srovnávací studie MeSH
• Názvy látek
• těkavé organické sloučeniny MeSH