Plant-ant interactions mediate herbivore-induced conspecific negative density dependence in a subtropical forest.

The early growth stage of plants is vital to community diversity and community regeneration. The Janzen-Connell hypothesis predicts that conspecific density dependence lowers the survival of conspecific seedlings by attracting specialist natural enemies, promoting the recruitment and performance of heterospecific neighbors. Recent work has underscored how this conspecific negative density dependence may be mediated by mutualists - such as how mycorrhizal fungi may mediate the accrual of host-specific pathogens beneath the crown of conspecific adult trees. Aboveground mutualist and enemy interactions exist as well, however, and may provide useful insight into density dependence that are as of yet unexplored. Using a long-term seedling demographic dataset in a subtropical forest plot in central China, we confirmed that conspecific neighborhoods had a significant negative effect on seedling survival in this subtropical forest. Furthermore, although we detected more leaf damage in species that were closely related to ants, we found that the presence of ants had significant positive effects on seedling survival. Beside this, we also found a negative effect of ant appearance on seedling growth which may reflect a trade-off between survival and growth. Overall, our findings suggested that ants and conspecific neighborhoods played important but inverse roles on seedling survival and growth. Our results suggest ants may mediate the influence of conspecific negative density dependence on seedling survival at community level.

Girdling behavior of the longhorn beetle modulates the host plant to enhance larval performance.

BACKGROUND: Preingestive behavioral modulations of herbivorous insects on the host plant are abundant over insect taxa. Those behaviors are suspected to have functions such as deactivation of host plant defenses, nutrient accumulation, or modulating plant-mediated herbivore interactions. To understand the functional consequence of behavioral modulation of insect herbivore, we studied the girdling behavior of Phytoecia rufiventris Gautier (Lamiinae; Cerambycidae) on its host plant Erigeron annuus L. (Asteraceae) that is performed before endophytic oviposition in the stem. RESULTS: The girdling behavior significantly increased the larval performance in both field monitoring and lab experiment. The upper part of the girdled stem exhibited lack of jasmonic acid induction upon larval attack, lowered protease inhibitor activity, and accumulated sugars and amino acids in compared to non-girdled stem. The girdling behavior had no effect on the larval performance of a non-girdling longhorn beetle Agapanthia amurensis, which also feeds on the stem of E. annuus during larval phase. However, the girdling behavior decreased the preference of A. amurensis females for oviposition, which enabled P. rufiventris larvae to avoid competition with A. amurensis larvae. CONCLUSIONS: In conclusion, the girdling behavior modulates plant physiology and morphology to provide a modulated food source for larva and hide it from the competitor. Our study implies that the insect behavior modulations can have multiple functions, providing insights into adaptation of insect behavior in context of plant-herbivore interaction.

Legacy effects of premature defoliation in response to an extreme drought event modulate phytochemical profiles with subtle consequences for leaf herbivory in European beech.

Extreme droughts can have long-lasting effects on forest community dynamics and species interactions. Yet, our understanding of how drought legacy modulates ecological relationships is just unfolding. We tested the hypothesis that leaf chemistry and herbivory show long-term responses to premature defoliation caused by an extreme drought event in European beech (Fagus sylvatica L.). For two consecutive years after the extreme European summer drought in 2018, we collected leaves from the upper and lower canopy of adjacently growing drought-stressed and unstressed trees. Leaf chemistry was analyzed and leaf damage by different herbivore-feeding guilds was quantified. We found that drought had lasting impacts on leaf nutrients and on specialized metabolomic profiles. However, drought did not affect the primary metabolome. Drought-related phytochemical changes affected damage of leaf-chewing herbivores whereas damage caused by other herbivore-feeding guilds was largely unaffected. Drought legacy effects on phytochemistry and herbivory were often weaker than between-year or between-canopy strata variability. Our findings suggest that a single extreme drought event bears the potential to long-lastingly affect tree-herbivore interactions. Drought legacy effects likely become more important in modulating tree-herbivore interactions since drought frequency and severity are projected to globally increase in the coming decades.

Pigeon pea crop stage strongly influences plant susceptibility to Helicoverpa armigera (Lepidoptera: Noctuidae).

Helicoverpa armigera Hübner (Lepidoptera: Noctuidae; Hübner) is the major insect pest of pigeon pea [Cajanus cajan; Fabales: Fabaceae; (L.) Millspaugh] worldwide. Research to develop pest management strategies for H. armigera in pigeon pea has focused heavily on developing less susceptible cultivars, with limited practical success. We examined how pigeon pea crop stage influences plant susceptibility to H. armigera using a combination of glasshouse and laboratory experiments. Plant phenology significantly affected oviposition with moths laying more eggs on flowering and podding plants but only a few on vegetative plants. Larval survival was greatest on flowering and vegetative plants, wherein larvae mostly chose to feed inside flowers on flowering plants and on the adaxial surface of expanding leaves on vegetative plants. Larval survival was poor on podding plants despite moths laying many eggs on plants of this stage. When left to feed without restriction on plants for 7 days, larvae feeding on flowering plants were >10 times the weight of larvae feeding on plants of other phenological stages. On whole plants, unrestricted larvae preferred to feed on pigeon pea flowers and on expanding leaves, but in no-choice Petri dish assays H. armigera larvae could feed and survive on all pigeon pea reproductive structures. Our results show that crop stage and the availability of flowers strongly influence pigeon pea susceptibility to H. armigera. An increased understanding of H. armigera-pigeon pea ecology will be useful in guiding the development of resistant varieties and other management tactics.

A theory for context-dependent effects of mammalian trampling on ecosystem nitrogen cycling.

Large mammalian herbivores substantially impact ecosystem functioning. As their populations are dramatically altered globally, disentangling their consumptive and non-consumptive effects is critical to advance mechanistic understanding and improve prediction of effects over ecosystem and Earth-system spatial extents. Mathematical models have played an important role in clarifying potential mechanisms of herbivore zoogeochemistry, based mostly on their consumptive effects as primary consumers and recyclers of organic and inorganic matter via defecation and urination. Trampling is a ubiquitous effect among walking vertebrates, but the consequences and potential mechanisms of trampling in diverse environments remain poorly understood. We derive a novel mathematical model of large mammalian herbivore effects on ecosystem nitrogen cycling, focusing on how trampling and environmental context impact soil processes. We model herbivore trampling with a linear positive or negative additive effect on soil-mediated nitrogen cycling processes. Combining analytical and numerical analyses, we find trampling by large mammalian herbivores is likely to decrease nitrogen mineralisation rate across diverse environments, such as temperate grassland and boreal forest. These effects are mediated by multiple potential mechanisms, including trampling-induced changes to detritivore biomass and functioning (e.g. rate of organic matter consumption). We also uncover scenarios where trampling can increase nitrogen mineralisation rate, contingent on the environment-specific relative sensitivity of detritivore mineral-nitrogen release and detritivore mortality, to trampling. In contrast to some consumptive mechanisms, our results suggest the pace of soil nitrogen cycling prior to trampling has little influence over the direction of the trampling net effect on nitrogen mineralisation, but that net effects may be greater in slow-cycling systems (e.g. boreal forests) than in fast-cycling systems (e.g. grasslands). Our model clarifies the potential consequences of previously overlooked mechanisms of zoogeochemistry that are common to all terrestrial biomes. Our results provide empirically testable predictions to guide future progress in empirical and theoretical studies of herbivore effects in diverse environmental contexts. Resolving ecological contingencies around animal consumptive and non-consumptive effects will improve whole-ecosystem management efforts such as restoration and rewilding.

Plant growth-defense trade-offs are general across interactions with fungal, insect, and mammalian consumers.

Plants face trade-offs between allocating resources to growth, while also defending against herbivores or pathogens. Species differences along defense trade-off axes may promote coexistence and maintain diversity. However, few studies of plant communities have simultaneously compared defense trade-offs against an array of herbivores and pathogens for which defense investment may differ, and even fewer have been conducted in the complex natural communities in which these interactions unfold. We tested predictions about the role of defense trade-offs with competition and growth in diversity maintenance by tracking plant species abundance in a field experiment that removed individual consumer groups (mammals, arthropods, fungi) and added nutrients. Consistent with a growth-defense trade-off, plant species that increased in mass in response to nutrient addition also increased when consumers were removed. This growth-defense trade-off occurred for all consumer groups studied. Nutrient addition reduced plant species richness, which is consistent with trade-off theory. Removing foliar fungi increased plant diversity via increased species evenness, whereas removal of other consumer groups had little effect on diversity, counter to expectations. Thus, while growth-defense trade-offs are general across consumer groups, this trade-off observed in wild plant communities does not necessarily support plant diversity maintenance.

Artificial light at night and warming impact grazing rates and gonad index of the sea urchin Centrostephanus rodgersii.

Artificial light at night (ALAN) is a growing threat to coastal habitats, and is likely to exacerbate the impacts of other stressors. Kelp forests are dominant habitats on temperate reefs but are declining due to ocean warming and overgrazing. We tested the independent and interactive effects of ALAN (dark versus ALAN) and warming (ambient versus warm) on grazing rates and gonad index of the sea urchin Centrostephanus rodgersii. Within these treatments, urchins were fed either 'fresh' kelp or 'treated' kelp. Treated kelp (Ecklonia radiata) was exposed to the same light and temperature combinations as urchins. We assessed photosynthetic yield, carbon and nitrogen content and C : N ratio of treated kelp to help identify potential drivers behind any effects on urchins. Grazing increased with warming and ALAN for urchins fed fresh kelp, and increased with warming for urchins fed treated kelp. Gonad index was higher in ALAN/ambient and dark/warm treatments compared to dark/ambient treatments for urchins fed fresh kelp. Kelp carbon content was higher in ALAN/ambient treatments than ALAN/warm treatments at one time point. This indicates ocean warming and ALAN may increase urchin grazing pressure on rocky reefs, an important finding for management strategies.

Simultaneous Impact of Rhizobacteria Inoculation and Leaf-Chewing Insect Herbivory on Essential Oil Production and VOC Emissions in Ocimum basilicum.

Inoculation with rhizobacteria and feeding by herbivores, two types of abiotic stress, have been shown to increase the production of secondary metabolites in plants as part of the defense response. This study explored the simultaneous effects of inoculation with Bacillus amyloliquefaciens GB03 (a PGPR species) and herbivory by third-instar Spodoptera frugiperda larvae on essential oil (EO) yield and volatile organic compound (VOC) emissions in Ocimum basilicum plants. The density of glandular trichomes was also examined, given that they are linked to EO production and VOC emission. Herbivory increased EO content, but inoculation on its own did not. When combined, however, the two treatments led to a 10-fold rise in EO content with respect to non-inoculated plants. VOC emissions did not significantly differ between inoculated and non-inoculated plants, but they doubled in plants chewed by the larvae with respect to their undamaged counterparts. Interestingly, no changes were observed in VOC emissions when the treatments were tested together. In short, the two biotic stressors elicited differing plant defense responses, mainly when EO was concerned. PGPR did not stimulate EO production, while herbivory significantly enhanced it and increased VOC emissions. The combined treatment acted synergistically, and in this case, PGPR inoculation may have had a priming effect that amplified plant response to herbivory. Peltate trichome density was higher in inoculated plants, those damaged by larvae, and those subjected to the combination of both treatments. The findings highlight the intricate nature of plant defense mechanisms against various stressors and hint at a potential strategy to produce essential oil through the combined application of the two stressors tested here.

Monitoring data on the effect of domestic livestock and rabbits on Androcymbiumeuropaeum (Lange) K. Richt. and its xerophytiques pastures for thirteen years.

Background: Dataset of annual monitoring of herbivory effects on the conservation status of the endangered species Androcymbiumeuropaeum (Lange) K. Richt and its associated plant communities is presented in this manuscript. This dataset encompasses the annual monitoring of herbivory effects on the conservation status of the endangered species Androcymbiumeuropaeum. Since 2010, the SERPAM Department (Service of Evaluation, Restoration and Protection of Mediterranean Agrosystems) at the Zaidin Experimental Station, belonging to the Spanish National Research Council (CSIC-EEZ), has conducted annual sampling to assess the impact of both domestic and wild livestock, specifically rabbits, on the pastures where A.europaeum lives. The study consisted of a randomised block design, implementing three distinct treatments to evaluate different management strategies: (1) rabbit and domestic herbivory, (2) exclusion of domestic livestock and (3) exclusion of rabbits and domestic livestock. Within each treatment, two types of monitoring were conducted. Firstly, the abundance of A.europaeum was estimated by counting individuals within 50 cm x 50 cm quadrats. Secondly, plant species diversity was assessed along 2-m long transects using the modified Point-Quadrat method. The research was conducted within the Cabo de Gata-Níjar Natural Park in southern Spain, specifically in the Amoladeras Nature Reserve in Almería. New information: The dataset contains information spanning from 2010 to 2023, providing valuable insights into the annual monitoring of herbivory effects on the conservation status of A.europaeum, contributing to our understanding of the species' interaction with domestic and wild animal in the studied area.

A pooled-sample draft genome assembly provides insights into host plant-specific transcriptional responses of a Solanaceae-specializing pest, Tupiocoris notatus (Hemiptera: Miridae).

The assembly of genomes from pooled samples of genetically heterogenous samples of conspecifics remains challenging. In this study, we show that high-quality genome assemblies can be produced from samples of multiple wild-caught individuals. We sequenced DNA extracted from a pooled sample of conspecific herbivorous insects (Hemiptera: Miridae: Tupiocoris notatus) acquired from a greenhouse infestation in Tucson, Arizona (in the range of 30-100 individuals; 0.5 mL tissue by volume) using PacBio highly accurate long reads (HiFi). The initial assembly contained multiple haplotigs (>85% BUSCOs duplicated), but duplicate contigs could be easily purged to reveal a highly complete assembly (95.6% BUSCO, 4.4% duplicated) that is highly contiguous by short-read assembly standards (N 50 = 675 kb; Largest contig = 4.3 Mb). We then used our assembly as the basis for a genome-guided differential expression study of host plant-specific transcriptional responses. We found thousands of genes (N = 4982) to be differentially expressed between our new data from individuals feeding on Datura wrightii (Solanaceae) and existing RNA-seq data from Nicotiana attenuata (Solanaceae)-fed individuals. We identified many of these genes as previously documented detoxification genes such as glutathione-S-transferases, cytochrome P450s, and UDP-glucosyltransferases. Together our results show that long-read sequencing of pooled samples can provide a cost-effective genome assembly option for small insects and can provide insights into the genetic mechanisms underlying interactions between plants and herbivorous pests.

Rich specialized insect damage on Pliocene leaves from the Mahuadanr Valley (India) growing under a warm climate with weak seasonality.

Plant-insect interactions play a crucial role in shaping terrestrial ecosystems, influencing abundance and distribution of plant species. In the present study, we investigated leaf-mining patterns on fossil leaves from Pliocene strata of the Mahuadanr Valley, Jharkhand, eastern India, deposited under a seasonal tropical climate, and reported complex interactions between plants and insects. We identified 11 distinct mining morphotypes. These morphotypes were mainly found on Dipterocarpaceae, Fabaceae, Lauraceae, and Moraceae; similar mining traces were also observed in the contemporary vegetation surrounding the fossil site. Although mining richness was relatively high, only 2.6% of all leaves in the fossil assemblage were mined. We compared mining richness and abundance values with previously reported values for galling. While richness was slightly lower for galling, almost 50% of all fossil leaves were galled. A literature survey on mining and galling patterns in modern vegetation suggests that there is no global explanation for richness of mining or gall-inducing insects. Thus, low nutrient availability in the ancient forest, dominance of semideciduous leaves with hard texture, and different habitats in the same forest ecosystem, such as well-drained forests and riparian stands, may all have favored different types of specialized plant-insect interactions.

Ontogenetic Changes in the Feeding Behaviour of Helicoverpa armigera Larvae on Pigeonpea (Cajanus cajan) Flowers and Pods.

Despite substantial research examining caterpillar-plant interactions, changes in the feeding behaviour of lepidopteran larvae as they develop are poorly understood. In this study, we investigated ontogenetic changes in the behaviour of Helicoverpa armigera larvae feeding on reproductive structures of pigeonpea (Cajanus cajan). Specifically, we examined the preference for and avoidance of pigeonpea flowers and pods of first, second, third, and fourth instar H. armigera larvae. We also conducted a no-choice assay to compare the ability of third and fourth instar larvae to penetrate pigeonpea pod walls, which act as a physical defence against herbivory. When presented with a choice between pigeonpea pods and flowers, different instars behaved differently. First and second instar larvae largely avoided pigeonpea pods, instead feeding on flowers; third instar larvae initially avoided pods, but by 24 h, did not strongly discriminate between the structures; and fourth instars demonstrated a preference for pods. When initially placed on pods, first instars were slower than other instars to leave these structures, despite pods being suboptimal feeding sites for small caterpillars. We identified a clear instar-specific ability to penetrate through the pod wall to reach the seeds. Most third instar larvae were unable to penetrate the pod wall, whereas most fourth instars succeeded. Third instars suffered a physiological cost (measured by relative growth rate) when boring through the pod wall, which was not observed in fourth instars. Our study further illuminates the insect-plant interactions of the H. armigera-pigeonpea system and provides evidence for the significant changes in feeding behaviour that may occur during lepidopteran larval development.

Comparative analyses of the banded alder borer (Rosalia funebris) and Asian longhorned beetle (Anoplophora glabripennis) genomes reveal significant differences in genome architecture and gene content among these and other Cerambycidae.

Rosalia funebris (RFUNE; Cerambycidae), the banded alder borer, is a longhorn beetle whose larvae feed on the wood of various economically and ecologically significant trees in western North America. Adults are short-lived and not known to consume plant material substantially. We sequenced, assembled and annotated the RFUNE genome using HiFi and RNASeq data. We documented genome architecture and gene content, focusing on genes putatively involved in plant feeding (phytophagy). Comparisons were made to the well-studied genome of the Asian longhorned beetle (AGLAB; Anoplophora glabripennis) and other Cerambycidae. The 814 Mb RFUNE genome assembly was distributed across 42 contigs, with an N50 of 30.18 Mb. Repetitive sequences comprised 60.27 % of the genome, and 99.0 % of expected single-copy orthologous genes were fully assembled. We identified 12657 genes, fewer than in the four other species studied, and 46.4 % fewer than for Aromia moschata (same subfamily as RFUNE). Of the 7258 orthogroups shared between RFUNE and AGLAB, 1461 had more copies in AGLAB and 1023 had more copies in RFUNE. We identified 240 genes in RFUNE that putatively arose via horizontal transfer events. The RFUNE genome encoded substantially fewer putative plant cell wall degrading enzymes than AGLAB, which may relate to the longer-lived plant-feeding adults of the latter species. The RFUNE genome provides new insights into cerambycid genome architecture and gene content and provides a new vantage point from which to study the evolution and genomic basis of phytophagy in beetles.

Spatio-temporal patterns of rangeland forage nutritive value and grazer selection with patch-burning in the US northern Great Plains.

Understanding how management influences forage nutritive value and grazer selection within grazing seasons is an ongoing effort for researchers and land managers globally. We used six, 65 ha pastures managed with patch-burn grazing and stocked with either cow-calf pairs (0.45-0.5 ha • AUM-1) or gestating ewes (0.4-0.48 ha • AUM-1) to explore how patterns in rangeland forage drive grazer selection in semi-arid rangeland over four summer grazing seasons at monthly intervals. We used near-infrared spectroscopy to determine nutritive value parameters from monthly forage clippings. We evaluated livestock performance as the average daily weight gains of each animal. We used mixed-effect models and ordination to compare patch and grazer types across the time-since-fire gradient and found that time-since-fire was significant for all measured variables. Cattle and sheep consistently preferred recently burned patches throughout grazing seasons. These recently burned patches typically contained available forage with higher crude protein and moisture content, lower biomass, and lower acid detergent fiber, acid detergent lignin, and neutral detergent fiber compared to intermediate time since fire patches and patches burned three years ago. Differences between patch-burn grazing with cattle and sheep were observed as additional patch contrasts for available biomass and crude protein, but grazer type and ecological site were not statistically significant factors for the nutritive value ordination. Our study indicates that patch-burn grazing is capable of imposing and maintaining heterogeneous, grazer selection, forage biomass, and nutritive value patterns desirable for heterogeneity focused land management, regardless of grazer type. These findings are especially relevant to the northern Great Plains where introduced grasses are homogenizing the structural environment of remaining rangelands. With prescribed fire currently an uncommon practice throughout the region, these findings provide a baseline of expectations for practitioners and land managers implementing patch-burn grazing and illustrate how grazing livestock can benefit from the patch contrast in forage nutritive value and biomass.

The double life of trichomes: understanding their dual role in herbivory and herbicide resistance.

Understanding the evolutionary forces that maintain phenotypic variation in ecologically relevant traits has long been one of the central goals of evolutionary ecology. While the maintenance of variation in plant defense is most often hypothesized to be due to trait trade-offs or spatio-temporal variation in herbivore abundance, the role that heterogeneous selective agents may play on the maintenance of variation in plant defense is less examined. Trichomes are hair-like appendages on plant surfaces that can defend against multiple damaging agents such as pathogens, herbivores, and UV radiation. It is currently unknown however if conflicting selection from such heterogeneous agents of damage may act to maintain the variation observed in trichome traits. Here, we assess whether trichomes serve as an herbicide resistance trait and how it coincides with the conventionally studied defensive strategy of herbivory resistance. In a series of experiments, we exposed the annual invasive velvetleaf (Abutilon theophrasti) to glyphosate (active ingredient in "Roundup") to investigate whether trichome traits (type and density) are linked to herbicide resistance and to test whether herbicide influences selection on plant trichomes. We found that an increased proportion of branched trichomes positively impacted herbicide resistance and chewing herbivory resistance. We also found evidence that glyphosate imposes positive selection on branched trichomes in velvetleaf. Overall, our results indicate that branched trichomes can contribute to both herbicide and herbivory resistance, serving a concordant rather than conflicting role to reduce plant injury. Our findings further suggest that novel anthropogenic agents of selection can alter the composition of plant defense traits, potentially impacting trait-mediated interactions among external stressors.

Quantum of fear: Herbivore grazing rates not affected by reef shark presence.

Grazing by nominally herbivorous fishes is widely recognised as a critical ecosystem function on coral reefs. However, several studies have suggested that herbivory is reduced in the presence of predators, especially sharks. Nevertheless, the effects of shark presence on grazing, under natural settings, remains poorly resolved. Using ∼200 h of video footage, we quantify the extent of direct disturbance by reef sharks on grazing fishes. Contrary to expectations, grazing rate was not significantly suppressed due to sharks, with fishes resuming feeding in as little as 4 s after sharks passed. Based on our observations, we estimate that an average m2 area of reef at our study locations would be subjected to ∼5 s of acute shark disturbance during daylight hours. It appears the short-term impact of reef shark presence has a negligible effect on herbivore grazing rates, with the variable nature of grazing under natural conditions overwhelming any fear effects.

Heterosis for Resistance to Insect Herbivores in a 3-Line Hybrid Rice System.

Three-line hybrid rice is produced by crossing male sterile (A line) rice with a fertility-restorer (R line). Fertile lines (B lines) are also required to maintain A line seed for breeding programs. We used a range of hybrids and their parental lines to assess the frequency and nature of heterosis for resistance to the whitebacked planthopper (Sogatella furcifera), brown planthopper (Nilaparvata lugens) and yellow stemborer (Scirpophaga incertulas). Heterosis is defined as trait improvement above the average of the parental lines as a result of outbreeding. Based on the results from a greenhouse study that challenged hybrids and their parental lines with each herbivore species, we found that susceptibility to planthoppers was associated with one of the eight A lines tested, but resistance was improved by crossing with a relatively resistant restorer. Higher frequencies of heterosis for susceptibility in comparisons between hybrids and their B lines suggest that susceptibility was not related to the cytoplasmic genomes of the associated sterile A lines. Furthermore, because none of the parental lines possessed currently effective resistance genes, improved resistance against planthoppers was probably due to quantitative resistance. In a related field trial, hybrids had generally higher yields than their fertile parents and often produced larger grain; however, they were often more susceptible to stemborers, leaffolders (Cnaphalocrocis medinalis) and other caterpillars (Rivula atimeta). This was largely a consequence of hybrid heterosis for plant biomass and was strongly affected by crop duration. We make a series of recommendations to improve hybrid breeding to reduce the risks of herbivore damage.

Limited Differences in Insect Herbivory on Young White Spruce Growing in Small Open Plantations and under Natural Canopies in Boreal Mixed Forests.

In managed boreal forests, both plantations and natural regeneration are used to re-establish a cohort of conifer trees following harvest or disturbance. Young trees in open plantations generally grow more rapidly than under forest canopies, but more rapid growth could be compromised by greater insect damage. We compared insect damage on white spruce (Picea glauca (Moench) Voss, Pinaceae) growing in plantations with naturally regenerated trees under mature forest canopies in boreal forests (Québec, Canada). We selected ten sites in the naturally regenerated forest and in small, multispecies plantations and sampled ten young trees of 2.5-3 m (per site) in late summer 2020 and again in early and late summer 2021. We compared overall rates of herbivory, galls (adelgids), damage by the spruce budworm (Choristoneura fumiferana, Clemens), and defoliation from sawflies. Overall, insect herbivory damage remained at similarly low levels in both habitats; an average of 9.3% of expanding shoots were damaged on forest trees and 7.7% in plantation trees. Spruce budworm damage increased from 2020 to 2021 and remained higher in under-canopy trees, but damage rates were negligible at this early stage of the outbreak (1.5% in forest vs. 0.78% of buds damaged on plantation trees). While damage due to galls was higher in plantations, the overall low level of damage likely does not pose a significant impact on the growth or mortality of young trees.

Neopolyploidy-induced changes in giant duckweed (Spirodela polyrhiza) alter herbivore preference and performance and plant population performance.

PREMISE: Polyploidy is a widespread mutational process in angiosperms that may alter population performance of not only plants but also their interacting species. Yet, knowledge of whether polyploidy affects plant-herbivore dynamics is scarce. Here, we tested whether aphid herbivores exhibit preference for diploid or neopolyploid plants, whether polyploidy impacts plant and herbivore performance, and whether these interactions depend on the plant genetic background. METHODS: Using independently synthesized neotetraploid strains paired with their diploid progenitors of greater duckweed (Spirodela polyrhiza), we evaluated the effect of neopolyploidy on duckweed's interaction with the water-lily aphid (Rhopalosiphum nymphaeae). Using paired-choice experiments, we evaluated feeding preference of the herbivore. We then evaluated the consequences of polyploidy on aphid and plant performance by measuring population growth over multiple generations. RESULTS: Aphids preferred neopolyploids when plants were provided at equal abundances but not at equal surface areas, suggesting the role of plant population surface area in driving this preference. Additionally, neopolyploidy increased aphid population performance, but this result was dependent on the plant's genetic lineage. Lastly, the impact of herbivory on neopolyploid vs. diploid duckweed varied greatly with genetic lineage, where neopolyploids appeared to be variably tolerant compared to diploids, sometimes mirroring the effect on herbivore performance. CONCLUSIONS: By experimentally testing the impacts of polyploidy on trophic species interactions, we showed that polyploidization can impact the preference and performance of herbivores on their plant hosts. These results have significant implications for the establishment and persistence of plants and herbivores in the face of plant polyploidy.