Leaf Herbivory Research Articles

Observed plant recovery of the endangered Cycas micronesica populations on the island of Guam: plant resistance or biocontrol

The island of Guam’s only gymnosperm and historically one of the island’s most abundant trees, Cycas micronesica, has been devastated by high mortality due primarily to the armoured scale Aulacaspis yasumatsui. This cycad-specific scale pest invaded Guam in 2003 and, in only a few years, this pest caused over 90% mortality to maturing trees and 100% mortality to seedlings. In 2015, C. micronesica was listed under the United States Endangered Species Act. Continuous surveillance of tree mortality throughout the island showed extreme decline in health until recent surveys have demonstrated that there has been improved tree health with little evidence of leaf herbivory on some remaining trees. Suggested explanations for this observed reduction in scale herbivory include some form of resistance in the surviving trees or a biocontrol agent (or several agents) that previously existed or has been introduced unintentionally and is controlling the scale to a greater degree. A combination of resistance and biocontrol are possibly both involved. We discuss in depth these possibilities and then propose experimental approaches that will help resolve this question.

Leaf herbivory causes abortion of selfed seeds in Rhododendron kaempferi var. kaempferi

AbstractPlant reproduction is often inhibited by herbivorous leaf damage, which affects the resource pool allocated for reproduction. Rhododendron kaempferi var. kaempferi is a semi‐evergreen shrub widely distributed in Japan, and its leaves are occasionally damaged by sawfly larvae (Arge similis). This species is partially self‐compatible, but its selfed seedlings suffer from inbreeding depression. Our study aimed to clarify (1) the magnitude of herbivorous damage under natural conditions, (2) the effects of foliage damage on seed number and mass, and (3) the possibility of selective abortion of selfed seeds to maintain outcrossed seed production under resource limitation. In the 2022 survey, 2 of the 20 ramets observed were collectively parasitized by sawfly larvae, and the most damaged ramet had a 59.6% foliage loss. In contrast, the herbivorous damage in 2023 was consistently low throughout the growing season, averaging a 3.2% loss. Leaf excision reduced the seed number per fruit (i.e., low seed‐set rate) but did not affect the individual seed mass. The outcrossing rate of the excision treatment (81.7%) was significantly higher than that of the control (72.0%). The values of seed‐set rate × outcrossing rate were 0.172 for the excision treatment and 0.171 for the control, nearly equal. Our results indicated that (1) sawfly larvae damage was concentrated on a few specific plants, (2) intense foliage damage reduced seed number but not seed mass, and (3) R. kaempferi mitigated the decline in outcrossed seed production by the abortion of selfed seeds when leaves were intensively damaged.

Heat wave impacts on crop‐pest dynamics are dependent upon insect ontogeny and plant resistance

AbstractHeat waves, brief periods of unusually high temperatures, are damaging to agroecosystems and are increasing in frequency and intensity due to climate change. Despite growing appreciation for the threat that heat waves pose to agricultural sustainability, we have a poor understanding of what determines their impact on agroecological interactions in the field. Here, we report the results of a field experiment that examined how heat waves and their timing interact with crop pest resistance to influence the interactions between potato (Solanum tuberosum) and its most damaging pest, the Colorado potato beetle (CPB; Leptinotarsa decemlineata). We used open‐top chambers and ceramic heaters to generate heat wave conditions in field plots with pest‐resistant and pest‐susceptible potato varieties at four CPB developmental stages. We then assessed CPB performance, leaf herbivory, and tuber yield. The neonate‐stage heat wave reduced larval survival by 10%, but the surviving larvae were 18% larger and developed 15% faster. However, these effects occurred only on the susceptible variety; both larval survival and growth were unaffected by the heat wave in the pest‐resistant variety. Moreover, the neonate‐stage heat wave reduced adult survival by 15%, suggesting negative carry‐over effects of early‐life heat exposure. Heat wave events after the neonate stage had no effects on CPB performance, crop damage, or tuber yield. Our results indicate that timing and pest resistance in crops are essential for understanding the impacts of extreme heat events on crop‐pest dynamics. Agroecological pest management in an increasingly variable and extreme climate will likely benefit from the development of strategies that account for the seasonal timing of potential heat events and from the continued use of crop varieties bred for pest resistance, which our results suggest may dampen the impacts of extreme temperatures on crop‐pest interactions.

Do leaf traits shape herbivory in tropical montane rainforests? A multispecies approach

AbstractThe co‐evolutionary arms race between herbivores and plants forces plants to evolve protection strategies that reduce the palatability of the plant modules attacked by the herbivores. These characteristics of traits have consequences for both the survival of plant individuals and the composition of plant communities. Thus, correlating traits of for instance leaves with herbivory is an important step toward understanding the dynamics of plant populations and communities. Traits can either be measured using conventional lab methods or recently developed spectral sensing techniques. We examined whether leaf traits of trees are related to herbivory in a multispecies approach. Furthermore, we explored whether leaf traits characterized by spectral sensing provide similar relations to herbivory as lab‐based leaf traits. We established nine 1‐ha square plots evenly distributed over three different forest types in Ecuadorian tropical montane rainforests where we estimated herbivory as the leaf area loss (in square centimeters) of 20 (±5) leaves sampled from the canopies of 380 tree individuals belonging to 51 tree species (7 ± 1 individuals/species) using lab‐ and spectral‐sensing‐based methods. For each methodological approach, we ran 100 linear mixed‐effects models with all respective leaf traits as predictor and herbivory as response variables for data subsets containing one randomly selected tree individual of each species to estimate the range of the regression coefficients for each trait. Automated stepwise backward selections determined the frequency of each trait having an important influence on herbivory. We found no clear relations between leaf traits and herbivory for neither lab‐ nor spectral‐sensing‐based traits. A nested variance component analysis demonstrated that the observed variability was mainly due to the variation in trait concentrations between tree individuals of a species. Our results suggest that snapshot data lead to a mismatch between herbivory and the concentrations of traits during the peak of herbivory. Another explanation could be that environmental conditions or processes along the food web are more important in structuring herbivory than leaf traits.

Insect seedling herbivory is influenced by multiple factors, but the plant apparency theory is more supported than other hypotheses – A case study in a subtropical forest

Insect herbivory is ubiquitous in various ecosystems, and directly influences the growth and survival of individual plants, especially during their vulnerable early life stages like the seedling phase. This, in turn, exerts a significant influence on forest community diversity and structure, as well as ecosystem function and stability. Notable variation in herbivory has been detected both among and within plant species. For decades, many hypotheses have been proposed to explain such variations, including both biotic and abiotic variables. However, most studies have considered only one or several of these hypotheses by focusing on a few potential variables, and their results were usually inconsistent; thus, the factors driving herbivory remain unclear. In this study, we examined leaf herbivory by insects of woody species seedlings in a subtropical forest in southwestern China over two seasons. In total, 24 potential variables that represented abiotic resource availability, characters of individual seedlings, conspecific and heterospecific species, and the whole seedling community were selected to test several commonly discussed alternative herbivory hypotheses. Overall, our findings showed that the plant apparency hypothesis was more supported than the other hypotheses in explaining insect seedling herbivory. Our results further indicated that the mechanisms and causes of insect herbivory are complex, multifactorial, species-specific and vary with seasons, indicating that there may be no uniform rules in explaining herbivory for all seedlings. Consequently, such complexity may play an important role in promoting species coexistence and biodiversity maintenance in seedling communities, which may further translate into the following generation of saplings or even adult communities. Changes in the community of insect herbivores and/or variables influencing insect herbivory, may disrupt stability of the original seedling community, thus affecting the regeneration and development of the entire forest community. Therefore, we suggest that issues related to insect herbivory should be considered when developing forest management and conservation.

Neighbourhood effects on herbivory damage and chemical profiles in short-rotation coppice willows and their hybrids

Short rotation coppices (SRCs) represent an important source of biomass. Since they are grown in various mixtures, SRCs represent an excellent opportunity for assessing the effects of local plant neighbourhoods on their performance. We used a common garden experiment consisting of plots that varied in genotype diversity of SRC willows to test for the effects of chemical traits of individual plants and chemical variation in the plots where they grew on insect herbivory. We also explored whether the composition of willows planted in a plot affected their chemistry. To do this, we performed untargeted metabolomics and quantified various chemical traits related to the total set of metabolites we detected, flavonoids, and salicinoids in four willow genotypes. We measured the leaf herbivory that the plants suffered. The genotypes differed in most chemical traits, yet we found only limited effects of individual traits on herbivory damage. Instead, herbivory damage was positively correlated with structural variation in salicinoids in a plot. When analysing the effects of plot chemical variation on herbivory damage separately for each genotype, we found both positive and negative correlations between the two, suggesting both associational resistance and susceptibility. Finally, we also observed a significant effect of the interaction between genotype and plot composition on structural variation in plant chemistry. Overall, our results suggest that high chemical variation in mixed willow SRCs does not necessarily lower the herbivory damage, possibly due to spillover effects of insect herbivores among genotypes. Our results also show that different genotypes respond differently to plot composition in terms of herbivory damage and chemical composition, which may affect their suitability for growing in mixed stands.

Artificial light at night decreases leaf herbivory in typical urban areas.

Artificial light at night (ALAN) is exerting growing pressure on natural ecosystems, but its impact on biological interactions remains unclear. This study aimed to assess how ALAN influences leaf functional traits and herbivory in two prevalent street tree species (Styphnolobium japonicum (L.) Schott and Fraxinus pennsylvanica) through field surveys and paired experiments in the urban areas of Beijing, China. We found that ALAN led to increased leaf toughness and decreased levels of leaf herbivory. Additionally, ALAN showed species-specific effects on leaf nutrients, size as well as defense substances. The findings illustrate that ALAN can significantly alter some key functional traits and ecological processes (nutrient cycling, energy flow). In general, we suggest that high ALAN intensity will be detrimental to the energy flow from urban plants to higher trophic levels, posing a potential threat to the maintenance of biodiversity (e.g., arthropod diversity, bird diversity) in urban ecosystems.

Long-term strict ant-plant mutualism identity characterises growth rate and leaf shearing resistance of an Amazonian myrmecophyte

Over 125 million years of ant-plant interactions have culminated in one of the most intriguing evolutionary outcomes in life history. The myrmecophyte Duroia hirsuta (Rubiaceae) is known for its mutualistic association with the ant Myrmelachista schumanni and several other species, mainly Azteca, in the north-western Amazon. While both ants provide indirect defences to plants, only M. schumanni nests in plant domatia and has the unique behaviour of clearing the surroundings of its host tree from heterospecific plants, potentially increasing resource availability to its host. Using a 12-year survey, we asked how the continuous presence of either only M. schumanni or only Azteca spp. benefits the growth and defence traits of host trees. We found that the continuous presence of M. schumanni improved relative growth rates and leaf shearing resistance of Duroia better than trees with Azteca. However, leaf herbivory, dry matter content, trichome density, and secondary metabolite production were the same in all trees. Survival depended directly on ant association (> 94% of trees died when ants were absent). This study extends our understanding of the long-term effects of strict ant-plant mutualism on host plant traits in the field and reinforces the use of D. hirsuta–M. schumanni as a model system suitable for eco-co-evolutionary research on plant–animal interactions.

Consistency of landscape compositional effects on microclimate, arthropods and plant performance across different years and regions

ContextReinforcement of agrobiodiversity in peri-urban areas requires a landscape lens. Relationships between land use composition and indicators of ecosystem services can depend on weather conditions and differ between regions.ObjectivesIn this study we present new empirical data on relationships between landscape composition and indicators of regulating and provisioning agroecosystem services. Furthermore, we check if these data are consistent between two different ecoregions and different years.MethodsWe apply an innovative methodology in a research landscape in the province of Antwerp (Flanders, Belgium) in 2021 with 1 m²-garden as phytometers along a landscape compositional gradient. Landscape composition at different scales is used as explanatory variable for microclimate variation, arthropod activity, leaf herbivory and crop yield in the 1 m²-gardens. Results are compared to an identical experiment in another ecoregion in East Flanders in 2018, 2019.ResultsWe found that the proportion of built-up areas is negatively related to local agroecosystem functioning. High-value herbaceous vegetation (e.g. extensive grasslands) promotes the activity of predators and high green vegetation buffers soil moisture and temperature variation, during dry and warm periods. Comparison between cases indicates that there is more consistency in the response of predatory invertebrates to the landscape composition than in the response of pollinators. The buffering effect of high green vegetation in the landscape increases when temperature and drought extremes occur.ConclusionsThe extent of high green vegetation can be enhanced at landscape level to maximise their ability to buffer extreme weather conditions. In peri-urban areas we should avoid further urban sprawl into the rural matrix and promote high-value herbaceous vegetation.

Native and invaded-range surveys provide mixed support for enemy-release of Nymphoides peltata in the invaded range

Natural or anthropogenic movement of plant species outside their historical ranges may result in exposure to new environmental conditions and a lack of natural enemies, thus promoting their establishment and spread into new areas. A biogeographical comparison of native and invasive populations can provide insight into the mechanisms of successful invasions and guide effective management strategies, such as biological control, by targeting plant traits that promote invasiveness. We studied the Eurasian aquatic plant, Nymphoides peltata, in situ in the native (China, Korea) and invaded (USA) ranges to determine whether there were differences in natural enemy attack rates (percent leaf damage, frequency of leaf herbivory or disease), productivity (plant cover, reproduction), and leaf traits (leaf elemental content, leaf toughness, dry matter content, specific leaf area) between areas. We also investigated whether there was evidence of a tradeoff between natural enemy attack and growth or reproduction, as would be predicted by invasion theory. Plant cover (23–29 % higher) and reproductive output (eight times more seeds / m2) were consistently higher in the invaded range. Leaf traits consistently differed between ranges, which we would expect if plants in the invaded range had fewer herbivores or other pests. The amount of leaf damage present was similar between ranges, but the frequency of herbivory was 50 % greater, on average, in the native than invaded range. Although we did not quantify suppression of N. peltata by natural enemies, we found evidence of more frequent herbivory in Asia and reduced reproduction and plant cover compared to the USA, which supports further investigation into viability of biological controls.

Insect herbivory on woody broadleaf seedlings along a subtropical elevational gradient supports the resource concentration hypothesis.

Theories of plant-herbivore interactions hold that seedlings are more vulnerable to herbivory in warmer and more stable climates at lower elevations. Hypotheses of plant apparency, resource concentration, and resource availability have been proposed to explain variability in leaf herbivory. However, seasonal differences in the effects of these hypotheses on leaf herbivory on seedlings remain unclear. We evaluated the three herbivory hypotheses by comparing the percentage and frequency of leaf herbivory in understory broadleaf seedlings in a subtropical forest in May (spring) and October (autumn) along an elevational gradient (290-1370 m a.s.l.). In total, we measured 2890 leaves across 696 seedlings belonging to 95 species and used beta regressions to test the effects of plant apparency (e.g., leaf area, seedling height), resource concentration (e.g., plant species diversity), and resource availability (e.g., canopy openness, soil available N and P) on leaf herbivory. Seedlings exhibited unimodal patterns of leaf herbivory along elevation, with drivers of leaf herbivory varying by the month. Variation in the frequency of leaf herbivory was best explained by the resource concentration hypothesis (e.g., plant species diversity) in both months, and herbivory was lower on seedlings in sites with higher plant diversity. Plant apparency hypothesis (e.g., leaf area, seedling height) was weakly supported only in spring, and the evidence for resource availability hypothesis (e.g., canopy openness, soil nutrients) was mixed. This study supports the resource concentration hypothesis and reveals the importance of seasonal difference on understanding leaf herbivory patterns and the drivers of plant diversity in subtropical forests.

Vaccinium dwarf shrubs responses to experimental warming and herbivory resistance treatment are species- and context dependent

Climate change impacts on species and ecosystem functioning may depend on climatic context and study systems. Climate warming and intensified herbivory are two stressors to plants that often appear in combination and are predicted to increase in cold environments. Effects of multiple drivers on plant performance are difficult to predict and warrant studies that use experimental manipulations along climatic gradients to produce more realistic knowledge. Our three study sites by the Sognefjord in Norway, that differed mainly in climatic conditions (ca. 5°C growing season difference), ranged from hemi-boreal lowland (100 masl, Low), via boreal mid-montane (500 masl) to alpine timberline (900 masl, High) bioclimates. At each site, in a randomized block design, we simulated growing-season warming using open-top chambers (OTCs) and experimentally induced herbivory resistance using the plant hormone methyl jasmonate (MeJA). We recorded growth, mortality, flower and fruit numbers, and insect herbivory on tagged ramets in permanent plots across three years (2016-2018) in three open woodland populations of two functionally important plant species with contrasting traits, Vaccinium myrtillus (bilberry) and V. vitis-idaea (lingonberry). Growth of both dwarf shrubs decreased with warming in the warm lowland populations (Low) but increased in the alpine populations (High). Shoot mortality increased most with warming at Low but was reduced at High. Reproduction, both flowering and fruiting, decreased with induced resistance treatment, but the effect was larger when warmed for bilberry and increased with elevation for both species. Leaf herbivory in bilberry increased with warming at Low but decreased at High. The combined warming and resistance treatment had only synergistic negative interaction effects on fruit numbers in bilberry. The clear context- and species-dependent effects of climate warming and increased resistance in this study may predict a potential decline in performance, as well as abundance and distribution, of these functionally important Vaccinium species at our lowest site. Bilberry reproduction appeared to be particularly susceptible to both climate warming and induced resistance in the manipulated populations. Such combined negative effects on plant performance are likely to have considerable knock-on effects via altered species’ interactions and ecosystem functioning.

Effects of Sun vs Shade and Leaf Age on Leaf Morphology, Herbivory, and Physical Defenses in the Swiss Cheese Plant (Monstera adansonii)

Abstract One important structural defense of plants is calcium oxalate crystals or raphides. In this project, I studied one species in the plant family Araceae, Monstera adansonii, a widely distributed plant in the tropics, that is known to contain raphides. Plants of this species were sampled in sun or shade locations. For each plant, three leaves were sampled, the first fully expanded leaf on a plant (leaf 1) and two more leaves below it, leaf 3 and leaf 5. For each leaf, I measured: leaf area, number of fenestrations (naturally occurring holes in the leaf), amount of herbivory, and density of raphides. I compared these measures on leaves of different ages from sun versus shade plants. Results showed that: 1) older leaves were significantly larger than younger leaves (P < 0.001), but there was no effect of light environment (P = 0.199); 2) density of raphides was not significantly affected by sun (P = 0.147) and density of raphides decreased with leaf age (P = 0.0097); 3) the number of fenestrations was significantly higher in plants in the sun (P = 0.01), but did not differ with leaf age (P = 0.702); 4) herbivory was not affected by sun exposure (P = 0.29) but was marginally significantly affected by raphide density (P = 0.06). There was a significant interaction between raphide density and light exposure on herbivory, in that in the shade there was a negative relationship where herbivory decreased as raphides increased, but in the sun, a positive relationship where herbivory increases as raphides increase (P = 0.04). Lay Summary Deforestation poses significant threats to the fragile ecosystem of tropical rainforests. Costa Rica’s Monteverde Cloud Forest, known for its rich biodiversity, relies on canopy tree cover for habitat protection and the maintenance of ecological balance. Tree loss can have a cascading effect on the ecosystem, which may negatively affect many species. When this balance is disrupted through deforestation, understory plants, such as Monstera adansonii, or the well-known “Swiss cheese” houseplant, are exposed to direct sun and harsh environmental elements. They may be initially ill-equipped to handle these conditions, but plants can physically adapt to their surrounding environment. To understand how plants may adapt to new conditions, I studied physical differences in Monstera adansonii between shaded understory areas and sunny exposed areas, which are created by forest clearing. I examined its physical differences, including the concentration of calcium oxalate crystals within its leaves. Among others, my results showed that the plants in the sun experienced more damage by herbivores than the plants in the shade. Through this study, I have “shed light” on the effects of deforestation and what this plant and many other understory plants may face as the rate of deforestation increases. For the full text, please visit https://scholar.colorado.edu/concern/undergraduate_honors_theses/d791sh621.

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 thatdrought 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.

Spatial and temporal variability in the structure of the multiple-herbivore community of horsenettle, and evidence for evolutionary responses in host-plant resistance

The geographic mosaic model of plant–herbivore coevolution asserts that interactions between a plant species and an herbivore species vary in intensity among populations across the plant’s geographic range. Despite this model’s intuitive appeal, data to investigate its implications for the type of complex, multiple-herbivore communities that occur in nature are scant. This paper reports on the results of 2 years of field surveys of damage by five leaf herbivores and one stem herbivore in four Solanum carolinense (horsenettle) populations, combined with results of a common-garden study quantifying the mean resistance levels of the plants from each field against each of the six herbivores. The relative amounts of damage caused by each species (representing the “herbivore-community structure”) differed significantly among the four fields. The plants were much more heavily damaged in the 2nd year than in the first, but the herbivore-community structure remained stable within each field between years. Overall, the amount of damage by species of herbivores in a field tended to be positively correlated with the plants’ levels of resistance that were measured in the common garden (r = 0.40, P = 0.05). Specifically, for five of the six herbivores, greater damage in the field was associated with greater plant resistance. This result suggests that horsenettle’s evolution of resistance against specific herbivores can occur rather quickly within fields, creating a local-scale mosaic of populations specifically adapted to the particular structure of the herbivore community that they are facing, but that herbivore-community structure is not strongly determined by plant resistance.

Temporal co-occurrence of leaf herbivory by chewers, leaf miners and gall-formers on a tropical tree: Do leaf traits matter?

Temporal co-occurrence of leaf herbivory by chewers, leaf miners and gall-formers on a tropical tree: Do leaf traits matter?

Volatile-mediated oviposition preference for healthy over root-infested plants by the European corn borer.

The selection of oviposition sites by female moths is crucial in shaping their progeny performance and survival, and consequently in determining insect fitness. Selecting suitable plants that promote the performance of the progeny is referred to as the Preference-Performance hypothesis (or 'mother-knows-best'). While root infestation generally reduces the performance of leaf herbivores, little is known about its impact on female oviposition. We investigated whether maize root infestation by the Western corn rootworm (WCR) affects the oviposition preference and larval performance of the European corn borer (ECB). ECB females used leaf volatiles to select healthy plants over WCR-infested plants. Undecane, a compound absent from the volatile bouquet of healthy plants, was the sole compound to be upregulated upon root infestation and acted as a repellent for first oviposition. ECB larvae yet performed better on plants infested below-ground than on healthy plants, suggesting an example of 'bad motherhood'. The increased ECB performance on WCR-infested plants was mirrored by an increased leaf consumption, and no changes in the plant primary or secondary metabolism were detected. Understanding plant-mediated interactions between above- and below-ground herbivores may help to predict oviposition decisions, and ultimately, to manage pest outbreaks in the field.

Endogenous rhythmic growth and ectomycorrhizal fungi modulate priming of antiherbivore defences in subsequently formed new leaves of oak trees

Abstract Priming of plant defences provides increased plant protection against herbivores and reduces the allocation costs of defence. Defence priming in woody plants remains obscure, in particular, due to plant development traits such as endogenous rhythmic growth. By using bioassays with oak microcuttings (Quercus robur) and combining transcriptomic and metabolomic analyses, we investigated how leaf herbivory by Lymantria dispar and root inoculation with the ectomycorrhizal fungus Piloderma croceum prime oak defences. We further investigated how defence priming is modulated by the rhythmic growth of the oaks. A first herbivory challenge in oak leaves primed newly grown leaves for enhanced induction of jasmonic acid (JA)‐related direct defences, or enhanced emission of volatiles, depending on the specific growth stage at which the plants were first challenged. Root inoculation with Piloderma abolished the enhanced induction of JA‐related defences and volatile emission. Synthesis: Our results indicate that a first herbivore attack primes direct and indirect defences of newly formed oak leaves and that the specific display of defence priming is regulated by rhythmic growth, and modulated by the interaction Piloderma. Our results show that the priming memory in oaks can be transmitted to the next growth cycle, to the leaves of the new shoot unit.

Effects of leaf herbivory and autumn seasonality on plant secondary metabolites: A meta-analysis.

Plant secondary metabolites (PSMs) are produced by plants to overcome environmental challenges, both biotic and abiotic. We were interested in characterizing how autumn seasonality in temperate and subtropical climates affects overall PSM production in comparison to herbivory. Herbivory is commonly measured between spring to summer when plants have high resource availability and prioritize growth and reproduction. However, autumn seasonality also challenges plants as they cope with limited resources and prepare survival for winter. This suggests a potential gap in our understanding of how herbivory affects PSM production in autumn compared to spring/summer. Using meta-analysis, we recorded overall production of 22 different PSM subgroups from 58 published papers to calculate effect sizes from herbivory studies (absence to presence) and temperate to subtropical seasonal studies (summer to autumn), while considering other variables (e.g., plant type, increase in time since herbivory, temperature, and precipitation). We also compared production of five phenolic PSM subgroups - hydroxybenzoic acids, flavan-3-ols, flavonols, hydrolysable tannins, and condensed tannins. We wanted to detect a shared response across all PSMs and found that herbivory increased overall PSM production in herbaceous plants. Herbivory was also found to have a positive effect on individual PSM subgroups, such as flavonol production, while autumn seasonality was found to have a positive effect on flavan-3-ol and condensed tannin production. We discuss how these responses might stem from plants producing some PSMs constitutively, whereas others are induced only after herbivory, and how plants produce metabolites with higher costs only during seasons when other resources for growth and reproduction are less available, while other phenolic PSM subgroups serve more than one function for plants and such functions can be season dependent. The outcome of our meta-analysis is that autumn seasonality changes some PSM production differently from herbivory, and we see value in further investigating seasonality-herbivory interactions with plant chemical defense.

Spider–Plant Interaction: The Role of Extrafloral Nectaries in Spider Attraction and Their Influence on Plant Herbivory and Reproduction

Spiders, abundant and diverse arthropods which occur in vegetation, have received little attention in studies investigating spider–plant interactions, especially in plants which have extrafloral nectaries (EFNs). This study examines whether spiders attracted to EFNs on the plant Heteropterys pteropetala (Malpighiaceae) function as biological protectors, mitigating leaf herbivory and positively impacting plant fitness, through manipulative experiments. Spiders are attracted to EFNs because, in addition to consuming the resource offered by these structures, they also consume the herbivores that are attracted by the nectar. At the same time, we documented the reproductive phenology of the plant studied and the abundance of spiders over time. Our results revealed that the plant’s reproductive period begins in December with the emergence of flower buds and ends in April with the production of samarids, fruits which are morphologically adapted for wind dispersal, aligning with the peak abundance of spiders. Furthermore, our results demonstrated that spiders are attracted to plants that exude EFNs, resulting in a positive impact on reducing leaf area loss but with a neutral effect on protecting reproductive structures. By revealing the protective function of spiders’ vegetative structures on plants, this research highlights the ecological importance of elucidating the dynamics between spiders and plants, contributing to a deeper understanding of ecosystems.