Foliar Quality Research Articles

Ecosystem‐wide responses to fire and large mammal herbivores in an African savanna

AbstractFire and large mammal herbivores (LMH) are the principal top‐down forces maintaining savanna structure. Nonetheless, experiments designed to investigate interactions between fire and LMH are rare in savannas, and relationships between environmental variation and biodiversity in the context of fire and LMH are poorly understood. This study addresses these gaps by manipulating the presence of LMH and early and late dry season fires in a tropical African savanna. In addition, this work simultaneously explores environmental variables including soil and foliar quality, vegetation cover, and nearby water sources to more holistically describe factors affecting savanna functioning and biodiversity. After 1 year of experimental treatments, changes in vegetation were already apparent. Shrub abundance and richness and grass richness were higher in the absence of LMH, while grass biomass increased three‐fold in burned plots as compared to unburned plots. Foliar nutrients tended to increase in open plots, while phenolics decreased. Amphibian abundance decreased with early burns and was higher with LMH. In contrast, small mammal abundance and richness increased without LMH and with time since fire. Richness and foraging of LMH were highest after late burns. These results demonstrate ecosystem‐wide effects of LMH, illustrating the importance of considering multiple taxa when designing fire management programs. For example, burning negatively affected amphibians and small mammals and changed vegetation at the same time it increased LMH foraging. In the long‐term, this experiment will shed light on interacting effects of fire and LMH on savanna biodiversity and function.Abstract in Portuguese is available with the online material.

From bottom‐up to top‐down control of invertebrate herbivores in a retrogressive chronosequence

In the long-term absence of disturbance, ecosystems often enter a decline or retrogressive phase which leads to reductions in primary productivity, plant biomass, nutrient cycling and foliar quality. However, the consequences of ecosystem retrogression for higher trophic levels such as herbivores and predators, are less clear. Using a post-fire forested island-chronosequence across which retrogression occurs, we provide evidence that nutrient availability strongly controls invertebrate herbivore biomass when predators are few, but that there is a switch from bottom-up to top-down control when predators are common. This trophic flip in herbivore control probably arises because invertebrate predators respond to alternative energy channels from the adjacent aquatic matrix, which were independent of terrestrial plant biomass. Our results suggest that effects of nutrient limitation resulting from ecosystem retrogression on trophic cascades are modified by nutrient-independent variation in predator abundance, and this calls for a more holistic approach to trophic ecology to better understand herbivore effects on plant communities.

Influence of reduced N-fertilizer application on foliar chemicals and functional qualities of tea plants under Toxoptera\xa0aurantii infestation

BackgroundThe tea aphid, Toxoptera aurantii (Boyer de Fonscolombe) is a polyphagous pest predominant in tea orchards and has become the most pernicious pest deteriorating tea quality. Nitrogen (N) is essential to plant growth improvement, and it can significantly impact plant defensive ability against aphid infestation. This study was designed to quantify the influence of reduced N-fertilizer application on foliar chemicals and functional quality parameters of tea plants against the infestation of T. aurantii. In this study, the tea seedlings (cv. Longjing43) were applied with normal level (NL) of N-fertilizer (240 kg N ha−1) along with reduced N-fertilizer levels (70%NL and 50%NL), and with and without T. aurantii infestation.ResultsThe results showed that N-fertilizer application significantly affected plant biomass and photosynthetic indexes, foliar soluble nutrients and polyphenols, tea catechins, caffeine, essential amino acids, volatile organic compounds of tea seedlings, and the population dynamics of T. aurantii. Compared with the normal N-fertilizer level, the reduced N-fertilizer application (70%NL and 50%NL) significantly decreased all the foliar functional quality components of tea seedlings without aphid infestation, while these components were increased in tea seedlings with aphid infestation. Moreover, the transcript expression levels of foliar functional genes (including CsTCS, CsTs1, and CsGT1) were significantly higher in the NL, and significantly lower in the 50%NL for tea seedlings without aphid infestation, while the transcript expression levels were significantly higher in 50%NL in aphid inoculated tea seedlings.ConclusionThe results demonstrated that the reduced N-fertilizer application could enhance foliar chemicals and functional quality parameters of tea plants especially with T. aurantii infestation, which can relieve soil nitrogen pressure and reduce pesticide use for control of tea aphid infestation in tea plantations.

European aspen with high compared to low constitutive tannin defenses grow taller in response to anthropogenic nitrogen enrichment

Boreal forests receive nitrogen-(N)-enrichment via atmospheric deposition and industrial fertilization. While it is known that N-enrichment can intensify interactions with natural antagonists, it remains poorly understood how genetic variability in plant defense chemistry can affect biotic interactions and height growth in N-enriched environments. We grew replicates of five low- and high-tannin Populus tremula genotypes, respectively, under three N-treatments (ambient, 15, and 150 kg N ha−1 yr−1). We assessed shoot blight occurrence (i.e. symptoms caused by Venturia fungi) during four growing seasons, and tree height growth during the same period. Damage by Venturia spp. increased with N-addition during all years, likely due to enhanced foliar quality. Low–tannin plants showed higher incidences of Venturia infection than high-tannin plants, regardless of the N-input-level. Height responded to an N-by-tannin-group interaction, which occurred because high-tannin plants grew taller than low-tannin plants at the high N-treatment, but not under the other N-levels. This pattern indicates that innate resource investment into tannin production yields a positive effect on growth under N-enriched conditions. Given that N-deposition is increasing globally, our research suggests that further studies are needed to investigate how N-enrichment interacts with plant defense traits globally. Moreover, our research suggests that N-deposition may provide an advantage for well-defended, high-tannin plants; and further, that genetic diversity in plant defense may be a key mechanism by which plant populations respond to this change.

Agronomic management of industrial hemp alters foliar traits and herbivore performance

Agronomic management decisions can alter plant foliar traits, especially nutritional quality, with potential to influence plant–herbivore interactions. Herbivores balance consumption of plant tissue for nutritional gains related to growth and development while contending with plant traits that may deter herbivory or are toxic. This study evaluates the influence of management decisions on the foliar quality of industrial hemp (Cannabis sativa) and the impact on the performance of fall armyworm (Spodoptera frugiperda). We included three common management decisions in this study: fertilization rate, cultivar choice, and planting date. In a no-choice feeding trial, fall armyworm larvae were fed leaves of field-grown hemp from three different cultivars that received different rates of fertilizer and were planted on two different dates. We quantified levels of foliar nitrogen, the ratio of carbon to nitrogen, leaf mass per unit area, and concentrations of tetrahydrocannabinol and cannabidiol, and determined the influence of foliar quality on herbivore performance. Fertilization rate, cultivar, and the interactions of planting date with both fertilization rate and cultivar influenced multiple aspects of hemp foliar quality. Overall, fertilization had the largest influence on foliar quality and subsequent herbivore performance. Variation in foliar traits influenced herbivore performance. Foliar nitrogen had a positive impact on fall armyworm performance and the ratios of carbon and total cannabinoids to nitrogen had negative impacts on fall armyworm performance. Our findings show that management decisions in industrial hemp can affect plant–insect interactions through changes in foliar quality. These outcomes suggest that developing crop management recommendations for pest management will be important for a re-emerging crop like industrial hemp.

Phenological responses to prior-season defoliation and soil-nutrient availability vary among early- and late-flushing aspen (Populus tremuloides Michx.) genotypes

Many spring-feeding insect folivores have evolved to hatch in synchrony with temporal windows of high foliar quality that occur during leaf expansion. In some host-tree species, however, budbreak phenology can shift in response to defoliation during the prior growing season. While this response could have important impacts on the performance of insect folivore species prone to multi-year outbreaks, the prevalence, underlying mechanisms, and ecological ramifications of defoliation-induced phenological shifts are poorly understood. We established a common garden of twelve trembling aspen (Populus tremuloides Michx.) genotypes, and observed the effects of prior-season defoliation and soil-nutrient availability on budbreak phenology during the following spring. Average budbreak phenology was delayed in response to both prior-season defoliation and low soil-nutrient treatments, but these responses were lower in magnitude than those previously shown to occur in response to temperature. Magnitudes of budbreak delay varied significantly among genotypes and were highest among early-flushing aspen. This negative correlation between aspen budbreak phenology and magnitudes of defoliation-induced phenological delay suggests that widespread defoliation could decrease intraspecific variation in aspen budbreak phenology during subsequent growing seasons, potentially allowing larvae to adapt to windows of optimal foliage quality during multi-year outbreaks. These results quantify additional environmental factors that may act in concert with major drivers such as temperature to mediate phenological relationships between aspen and folivorous insects.

Tight insect–host phenological synchrony constrains the life‐history strategy of European pine sawfly

AbstractThe synchronization of insect and plant phenologies may impose ecological constraints on host specialization and the evolution of life histories. European pine sawfly Neodiprion sertifer (Geoffroy) feeds on mature foliage of Scots pine Pinus sylvestris L. during a limited temporal period in early spring and is univoltine despite the continual presence of this resource throughout the growing season. Reciprocal manipulation of host and insect phenologies demonstrated that larval performance was highest in mid‐April, with the window of host susceptibility closing rapidly thereafter. As the host phenology advanced, the foliar concentration of nitrogen, amino acids and soluble carbohydrates decreased, whereas that of terpenoids increased. As the foliar quality declined, larvae ate more in an attempt to compensate, although they were less efficient at converting consumed foliage to body mass. The phenological window for larval development began to reopen late in the growing season as the quality of mature foliage started to improve until it once again supported larval development during the next spring. Neodiprion sertifer must synchronize its life cycle with an ephemeral phenological window of host suitability that closes too early and reopens too late to permit a second generation.

INFLUENCE OF FOLIAR SPRAYS ON YIELD AND QUALITY OF BARAMASI LEMON.

08Jun 2018 INFLUENCE OF FOLIAR SPRAYS ON YIELD AND QUALITY OF BARAMASI LEMON. Jobanjit Singh and Amarjeet Kaur. Department of Horticulture(Agriculture)Khalsa College, Guru Nanak Dev University, Amritsar-143001.

O3-Induced Leaf Senescence in Tomato Plants Is Ethylene Signaling-Dependent and Enhances the Population Abundance of Bemisia tabaci.

Elevated ozone (O3) can alter the phenotypes of host plants particularly in induction of leaf senescence, but few reports examine the involvement of phytohormone in O3-induced changes in host phenotypes that influence the foraging quality for insects. Here, we used an ethylene (ET) receptor mutant Nr and its wild-type to determine the function of the ET signaling pathway in O3-induced leaf senescence, and bottom-up effects on the performance of Bemisia tabaci in field open-top chambers (OTCs). Our results showed that elevated O3 reduced photosynthetic efficiency and chlorophyll content and induced leaf senescence of plant regardless of plant genotype. Leaf senescence in Nr plants was alleviated relative to wild-type under elevated O3. Further analyses of foliar quality showed that elevated O3 had little effect on phytohormone-mediated defenses, but significantly increased the concentration of amino acids in two plant genotypes. Furthermore, Nr plants had lower amino acid content relative to wild-type under elevated O3. These results provided an explanation of O3-induced increase in abundance of B. tabaci. We concluded that O3-induced senescence of plant was ET signal-dependent, and positive effects of O3-induced leaf senescence on the performance of B. tabaci largely resulted from changes of nutritional quality of host plants.

Subtropical Tritrophic Interactions Under Elevated CO2 and Temperature Conditions.

The effects of climate change and extreme weather conditions on plants and animals have been documented extensively. However, the possible effects of these factors on plant-insect interactions in subtropical regions are relatively unexplored. The present study investigated the consequences of elevated CO2 and temperature on a tritrophic system (plant-insect-parasitoid) in subtropical regions. The experimental conditions were as follows: ambient CO2, 500 ppm; elevated CO2, 1,000 ppm; ambient temperature, 24/21°C (day/night); and elevated temperature, 29/26°C (day/night). Brassica oleracea var. italica foliar primary metabolites were quantified 6 wk after germination and insect feeding bioassays were subsequently conducted. Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) larvae were fed directly on these plants until pupal development. In addition, the second instar S. litura larvae were exposed to the parasitoid Snellenius manilae (Ashmead) (Hymenoptera: Braconidae) under the same plant treatment conditions. The results suggested that elevated CO2 has a major influence on plant performance and foliar quality. Elevated CO2 also affected the leaf area, foliar fresh and dry weights, and total nitrogen and carbohydrate contents. Elevated temperature reduced the larval development time and increased the growth rate of S. litura. Sn. manilae had a higher parasitism rate and shorter development time at elevated temperature compared with ambient temperature. These results suggested that the dynamic and communal structure of S. litura and its parasitoids requires comprehensive evaluation in terms of the changes in nutritional quality (bottom-up control) caused by the interactive effects of CO2 and temperature.

Defining the window of opportunity for feeding initiation by second-instar spruce budworm larvae

Establishing feeding sites is critical for the survival of neonate Lepidoptera larvae. Rapid foliar quality changes during leaf expansion create a narrow window of opportunity for establishment of early-spring feeders. We examined the effect of phenological synchrony between black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.) and balsam fir (Abies balsamea (L.) Mill.) budbreak and spruce budworm (Choristoneura fumiferana (Clemens)) emergence on the feeding behaviour of young larvae and on overall larval growth and survival under laboratory conditions. We correlated these variables with bud development and foliar toughness during the growing season. Our results show that early-emerging second-instar larvae were unable to feed on either black spruce or balsam fir buds; budworm on balsam fir mined old foliage and exhibited good survival and performance, but those on black spruce remained on the foliar surface and suffered high mortality and low growth. In the second later-emerging cohort, bud feeding gradually increased on black spruce whereas it was already the predominant behaviour on balsam fir, and no differences in performance were observed between host species. Thus, black spruce budbreak constitutes a strict window of opportunity, since larvae are often unable to mine the old foliage. Our results suggest that mechanical toughness could be the obstacle preventing young larvae from mining old black spruce needles. Our findings confirm the importance of second-instar ecology in spruce budworm, suggesting that, if climate warming eventually results in an improvement in phenological synchrony between spruce budworm and black spruce, larval survival may increase.

Ontogenetic changes in insect herbivory in birch (Betula pubesecens): The importance of plant apparency

Abstract Several theories aim at predicting changes in the interactions between plants and herbivores over the lifetime of a plant. Hypotheses based on ontogenetic changes in resource allocation to plant defence and in plant apparency lead to partly opposing predictions regarding the differences in levels of herbivory between juvenile and mature plant individuals. We tested these predictions by measuring background foliar losses to insects in saplings and mature trees of downy birch (Betula pubescens) in ten sites along a latitudinal gradient from 60° to 69°N in boreal forests of Northern Europe. The percentage of consumed leaf area increased, and the variation in the levels of herbivory among plant individuals decreased, for tree sizes ranging from small saplings (2–12 cm tall) to large saplings (13–80 cm tall) and then to mature trees (3–18 m tall). Small saplings had higher foliar quality for insects, as indicated by better performance of leafmining larvae of Eriocrania semipurpurella and by greater specific leaf area, compared with large saplings and mature trees. The average percentage of leaf area consumed from a damaged leaf, which reflects the inducibility of local defence responses to insect damage, did not vary among the birch size classes. The foliar losses to insects decreased nearly fivefold with an increase in latitude from 60° to 69°N, but the relative differences in these losses among the birch size classes were independent of latitude. Our findings fit well with the predictions based on a plant apparency hypothesis, but do not support predictions based on ontogenetic changes in resource allocation to plant antiherbivore defences. We conclude that the generally overlooked effects of apparency on plant damage by insects can explain, at least in some cases, the frequently observed lack of correspondence between the levels of plant defences and herbivory. A plain language summary is available for this article.

Responses of root exudation and nutrient cycling to grazing intensities and recovery practices in an alpine meadow: An implication for pasture management

The rhizosphere priming effect is caused by root carbon (C) exudation into the rhizosphere; the role of this effect in nutrient cycling and ecosystem recovery of natural grasslands as affected by different grazing intensities is still unknown. The objective of the present study was to investigate the relationships among root C exudation, rhizospheric microbial activity, and their influences on plant nutrient uptake during grazing and recovery periods. Field experiments were conducted in the Hongyuan Alpine Meadow to measure root exudation rate and nutrient cycling processes of the dominant species Elymus nutans. Three grazing intensities (an ungrazed control, moderate grazing and heavy grazing) were introduced for two months, following which all treatments received a recovery practice (no grazing for 21 days). Heavy grazing significantly decreased root exudation rate, soil nitrogen (N) mineralization rate, β-1,4-glucosidase (BG) activity, and foliar C concentration, while moderate grazing had no influence on these parameters compared to the control. After the 21 days of recovery, all these parameters, except N mineralization rate and foliar C concentrations in the heavy grazing treatment, returned to similar levels as in the control, whereas root exudation rate and BG activity rose to even higher levels. Meanwhile, moderate grazing significantly promoted root exudation rate, soil inorganic N concentration, net soil N mineralization rate, and β-N-acetylglucosaminidase (NAG) activity during the recovery stage as compared to the control. Foliar quality was also improved by the recovery practice, indicating that the high availability of N and P is a consequence of the positive root–microbe feedback and will ultimately benefit grazers. The flush of labile C released to the rhizosphere by grazed plants stimulated extracellular enzyme activities, enhanced soil N mineralization, and increased plant nutrient uptake. These results imply that reasonable (i.e. moderate) grazing followed by a recovery practice can effectively restore and strengthen grassland vegetation, and contribute to the sustainable use of alpine meadows such as Hongyuan.

Density-dependent effects of larval dispersal mediated by host plant quality on populations of an invasive insect.

The success of invasive species is often thought to be due to release from natural enemies. This hypothesis assumes that species are regulated by top-down forces in their native range and are likely to be regulated by bottom-up forces in the invasive range. Neither of these assumptions has been consistently supported with insects, a group which includes many destructive invasive species. Winter moth (Operophtera brumata) is an invasive defoliator in North America that appears to be regulated by larval mortality. To assess whether regulation was caused by top-down or bottom-up forces, we sought to identify the main causes of larval mortality. We used observational and manipulative field and laboratory studies to demonstrate that larval mortality due to predation, parasitism, and disease were minimal. We measured the response of larval dispersal in the field to multiple aspects of foliar quality, including total phenolics, pH 10 oxidized phenolics, trichome density, total nitrogen, total carbon, and carbon-nitrogen ratio. Tree-level declines in density were driven by density-dependent dispersal of early instars. Late instar larvae dispersed at increased rates from previously damaged as compared to undamaged foliage, and in 2015 field larval dispersal rates were related to proportion of oxidative phenolics. We conclude that larval dispersal is the dominant source of density-dependent larval mortality, may be mediated by induced changes in foliar quality, and likely regulates population densities in New England. These findings suggest that winter moth population densities in New England are regulated by bottom-up forces, aligning with the natural enemy release hypothesis.

Foliar quality of co-occurring mallee eucalypts: balance of primary and secondary metabolites reflects past growing conditions

Foliar quality for herbivores is determined by the balance of primary and secondary metabolites which is dependent on leaf age which in turn is determined by the periodicity of flushing and the rate of abscission. We conducted a 10-month longitudinal study in northeastern Victoria, Australia, of the quality of fully expanded leaves of Eucalyptus gracilis, E. socialis, E. dumosa and E. incrassata. We measured N and available N (AvailN) as well as sideroxylonals and other formylated phloroglucinol compounds (FPCs) and related changes in concentration to tree phenology (flushing and flowering) and climatic conditions (temperature and rainfall). Concentrations of N, sideroxylonals and other FPCs differed significantly between species and with time as well as among trees within a species. AvailN also differed significantly between species and among trees within a species and with time for E. gracilis. Our analyses indicated that tree phenology affected N concentrations in E. gracilis only while climatic conditions affected N concentrations in E. gracilis, E. socialis and E. dumosa. Nitrogen concentrations in E. incrassata were unaffected by phenological or climatic factors. Tree phenology affected concentrations of sideroxylonals in E. gracilis and E. dumosa while climatic conditions affected concentrations of the same in E. socialis, E. dumosa and E. incrassata. The concentration of primary metabolites in expanded leaves of these eucalypts was relatively consistent compared to the concentration of quality reducing secondary metabolites which varied with the conditions experienced when leaves were expanding. Our results show that the foliar quality of leaves can be highly variable, with variations mediated by phenology and climate. These variations are likely to partially explain fluctuations in the abundance of chewing insect herbivores reliant on expanded leaves.

Is tropical montane forest heterogeneity promoted by a resource‐driven feedback cycle? Evidence from nutrient relations, herbivory and litter decomposition along a topographical gradient

SummaryRidges of tropical mountains often differ strikingly from neighbouring ravines in terms of forest structure, productivity and species composition. This heterogeneity is poorly understood despite its critical role in biodiversity maintenance, carbon and nutrient budgets.We examined measures of tree biomass and productivity, foliage and litter quality (nutrient concentrations, specific leaf mass, phenolics), herbivory and leaf litter decomposition in each six plots laid out in upper and lower slope position in a tropical montane moist forest in southeastern Ecuador.Productivity, quality of foliage and litter as well as herbivory were significantly lower in upper slope position, and closely correlated with soil nutrient concentrations and accumulated humus. The decomposition of upper slope leaf litter (decomposition ratek) was substantially lower than in litter from lower slope forest, whereas the site of decomposition (slope position) only had a marginal effect on the decomposition rate.Our results suggest that the differences in stand structure, productivity, foliar quality, herbivory and decomposition between slope positions are ultimately due to stronger nutrient limitations in upper slope forest. We propose a general conceptual model that explains origin and maintenance of contrasting forest types along topographical gradients through down‐slope fluxes of nutrients and water, and a nutrient‐driven positive feedback cycle.

Divergent responses of leaf herbivory to simulated hurricane effects in a rainforest understory

Hurricanes are major disturbances in many forests, but studies showing effects of natural hurricanes on herbivory rates have yielded mixed results. Forest managers could benefit from a better understanding of the effects of disturbances on herbivory to manage for particular recovery or restoration goals after anthropogenic or natural disturbances, such as logging and windstorms. I measured herbivory on eight understory plant species that are common pioneer and non-pioneer species in a rainforest in Puerto Rico, following experimental manipulation of forest plots to simulate the two major effects of a hurricane (canopy opening and a detrital pulse). I expected that greater leaf production and leaf quality would result from canopy trimming and detritus (debris) addition to the forest floor, respectively, and that both treatments would enhance herbivory rates independently and especially in combination. I found a significant interaction of trim and debris treatments that affected plant species within pioneer and non-pioneer plant groups differently: a debris pulse or canopy trimming alone stimulated understory herbivory over time on non-pioneer and pioneer plants, respectively, but the combination of these two treatments had no effect on herbivory rates. Specifically, herbivory was higher on pioneer plants in plots where the canopy was trimmed but debris had not been added, whereas herbivory was higher on non-pioneer plants in plots where debris was added to the forest floor under intact canopy conditions. Therefore, different mechanisms apparently controlled herbivory of pioneer and non-pioneer species. Pioneer plants likely experienced enhanced herbivory in trimmed plots in part because of the increased densities of pioneer plants responding to canopy trimming; pioneer plants were temporarily less abundant in debris addition plots. Non-pioneer species may have experienced greater herbivory in debris addition plots in part because of increased foliar quality resulting from enhanced nutrient availability associated with the debris pulse. Future, complementary greenhouse and field mesocosm experiments that manipulate the factors likely contributing to these results would help to reconcile results from previous studies that have documented both increases and decreases in herbivory or certain herbivore taxonomic groups resulting from natural hurricanes. Understanding the mechanisms that affect herbivory after hurricanes is important because herbivory can affect nutrient cycling, plant community structure, and ultimately forest recovery after disturbance.

Moth communities and agri‐environment schemes: Examining the effects of hedgerow cutting regime on diversity, abundance, and parasitism

Abstract Hedgerows provide an important habitat for wildlife including invertebrates, representing a large proportion of semi‐natural habitat patches in the modern agricultural landscapes of the UK and Europe. Around 40% of hedgerow length in England is managed under agri‐environment scheme (AES) options, which specify less frequent cutting and advise cutting in winter. Hedgerow management can alter habitat structure and quality, potentially influencing invertebrate community structure. We assessed the impacts of management treatments on moth communities and their parasitoids. Two treatments (‘cutting frequency’: once every 1, 2, or 3 years, and ‘cutting time’: autumn vs. winter) were applied to a long‐running hedgerow experiment, mimicking AES prescriptions. Moth larvae were collected from the hedgerows, identified and reared to determine parasitism. Hedgerow structure and foliar quality were quantified and related to changes in moth abundance, diversity, species richness, and parasitism. Hedgerow management did not significantly affect overall abundance of moth larvae, but did affect the abundance of certain feeding guilds and trophic interactions with parasitoids. Concealed moth larvae (mining, tentiform, and case bearing) were more abundant on hedgerows cut infrequently (every 2 or 3 years vs. annually). Parasitism rates were higher on hedgerows cut less often, when these were cut in autumn. There was a strong trend towards greater moth species richness and diversity on winter cut hedgerows. Agri‐environment scheme management can thus have complex effects on invertebrate communities. The abundance of some moths may be positively affected by AES hedgerow management and this can have knock‐on effects on parasitoid abundance.

Terrestrial deposition of aquatic insects increases plant quality for insect herbivores and herbivore density

1. Mobile organisms such as emergent aquatic insects can subsidise land with aquatic nutrients, creating a link between terrestrial and aquatic ecosystems.2. Deposition of aquatic insects on land produces bottom‐up effects in arthropod detritivore communities and may also affect plants and plant–herbivore interactions.3. To investigate the effects of insect deposition on plant–herbivore interactions, we conducted a field experiment and surveys of tealeaf willow (Salicaceae; Salix phylicifolia Coste) and July highflyer caterpillars (Geometridae; Hydriomena furcata Thunberg) at lakes in Northeast Iceland with either high‐ or low‐midge density and deposition to land.4. It was found that willow at high‐midge lakes had 8–11% higher nitrogen content compared with willow at low‐midge lakes. In addition, natural caterpillar density was 4–6 times higher and caterpillars were 72% heavier at high‐midge lakes than low‐midge lakes.5. A fully reciprocal caterpillar transplant experiment among willow at high‐ and low‐midge lakes was performed to separate the influence of habitat and midge effects on caterpillar performance.6. After transplant, pupae of July Highflyer caterpillars were on average 11% heavier at high‐midge sites compared with low‐midge sites. However, this difference was not statistically significant.7. The present findings indicate that cross‐ecosystem subsidies in the form of aquatic insects can increase plant foliar quality and the abundance of insect herbivores in recipient ecosystems.

Atmospheric change alters frass quality of forest canopy herbivores

This study examined the independent and interactive effects of elevated atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) on the foliar and litter chemistry of two deciduous tree species and the frass chemistry of four lepidopteran folivores. Trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera) were grown under elevated levels of CO2 and/or O3 at the Aspen FACE research site in northern WI, USA. We measured the effects of CO2 and O3 on nitrogen, carbon to nitrogen (C:N), and condensed tannin levels in aspen and birch leaves and senescent litter and also in the frass of folivores fed aspen or birch green leaves. Overall, the effects of elevated CO2 on foliar chemistry were less pronounced than those of elevated O3, and aspen responded more strongly than birch. While the effects of elevated CO2 and O3 on foliar chemistry were generally reflected in frass chemistry, the magnitude of the response varied among insect species. Insect frass had higher nitrogen and condensed tannin levels and lower C:N ratios than did litter, although the magnitude of this response varied among fumigation treatments and insect species. Our findings demonstrate that the quality of insect-mediated organic deposition can be indirectly affected by atmospheric change, through altered foliar quality. Our findings also suggest that the quality of frass deposited on the forest floor via herbivory will be strongly affected by herbivore community composition.