Spatial patterns of insect herbivory within a forest landscape:the role of soil type and forest stratum

Background:Insect herbivory has profound impacts on ecosystem processes and services.Although many efforts have been made to recognize the main drivers of insect herbivory at different scales,the results are inconsistent.One likely reason is that studies have insufficiently captured the spatially heterogeneous factors such as soil type and forest stratum within the stand that may significantly affect insect herbivory.In particular,there is a lack of studies that address the detailed spatial patterns of insect herbivory which are influenced by these factors.Methods:We measured the detailed spatial patterns of insect herbivory on cork oak(Quercus variabilis Bl.)in response to soil type(gravel soil and loam)and forest stratum(the upper,lower,and sapling stratum),and correlated these patterns with a set of influencing factors(litter coverage,coverage of shrubs and herbs,soil nutrients,soil moisture,and leaf traits)in a forest landscape.Results:Generally,insect herbivory was spatially heterogeneous within stands.Herbivory was significantly lower in gravel soil areas than in loam soil areas and the highest herbivory occurred in the lower stratum.However,there were also 41 individual plots in which the highest herbivory occurred in the upper stratum and 29 plots in which the highest herbivory occurred in the sapling stratum.There were significant differences in soil nutrient and water status between soil types,but no significant differences in leaf traits.The effects of forest stratum on leaf traits were also inconsistent with those on insect herbivory.Conclusions:Leaf traits may not be the main factors influencing insect herbivory in the field.Soil type may have major effects on herbivory patterns by influencing litter coverage while higher coverage of shrubs and herbs may reduce herbivory in the sapling stratum.These findings may advance our understanding of tree-herbivore interactions in real-world situations and have important implications for the sustainable management of forest ecosystems.

A New Species of Rhodoleia(Hamamelidaceae) from the Upper Pliocene of West Yunnan, China and Comments on Phytogeography and Insect Herbivory

In Europe, fossil fruits and seeds of Rhodoleia（Hamamelidaceae） have been described from the Upper Cretaceous to the Miocene, whereas no fossil record of Rhodoleia has been reported in Asia, where the modern species occur.Herein, 21 fossil leaves identified as Rhodoleia tengchongensis sp.nov.are described from the Upper Pliocene of Tengchong County, Yunnan Province, Southwest China.The fossils exhibit elliptic lamina with entire margins, simple brochidodromous major secondary veins, mixed percurrent intercostal tertiary veins, and looped exterior tertiaries.The leaf cuticle is characterized by pentagonal or hexagonal cells, stellate multicellular trichomes, and paracytic stomata.The combination of leaf architecture and cuticular characteristics suggests that the fossil leaves should be classified into the genus Rhodoleia.The fossil distributions indicate that the genus Rhodoleia might originate from Central Europe, and that migrated to Asia prior to the Late Pliocene.Additionally, insect damage is investigated, and different types of damage, such as hole feeding, margin feeding, surface feeding, and galling, are observed on the thirteen fossil leaves.Based on the damage frequencies for the fossil and extant leaves, the specific feeding behavior of insects on Rhodoleia trees appears to have been established as early as the Late Pliocene.The high occurrence of Rhodoleia insect herbivory may attract the insect-foraging birds, thereby increasing the probability of pollination.

Premature losses of leaf area in response to drought and insect herbivory through a leaf lifespan gradient

Implications of the differences in leaf life span are still subject to debate in the field of ecophysiology.Since leaf traits associated with these differences may be decisive for determining the distribution of tree species,this topic is particularly relevant in the context of climate change.This study analyzes the effects of the differences in leaf life span on premature losses of leaf area owing to insect herbivory and to abiotic stress.Loss of leaf area may be an important determinant of total leaf carbon assimilation.Seven Mediterranean tree species,distributed on four sites with different climates were studied.The species exhibited strong differences in leaf life span and in leaf traits,especially leaf mass per unit area.Premature leaf area losses were estimated in response to insect herbivory and summer drought over two years.The results revealed that,despite having older leaf cohorts with more damage,species with longer leaf duration had lower area lost to herbivores and less damage due to accelerated senescence during the summer drought.With respect to the predicted increase in water stress,deciduous species are at a disadvantage due to their high premature loss of leaf area and thus loss of photosynthetic capacity.

Defensive Role of Plant Latex on Insect Pests’ Suppression: A Critical Review

Over 350 million years have passed since the documentation of the first interaction between plants and insects. Numerous plant defense qualities and associated counter-adaptive features have developed as a result of these interactions between insects and plants. These characteristics might be either morphological or biological in nature. One of the most significant and useful biochemical characteristics in plants is latex. Latex has a sticky property due to presence of secondary metabolites in it, which aids in entangling or sealing the mouthparts of small insects. These metabolites also chemically interact with the insects interfering with crucial bodily processes. Plant latex has amazing properties that help protect plants from insects and inhibit them in general. It may be possible to control insect pests in a natural, secure, and long-lasting manner by correctly identifying plant latex with strong insecticidal properties and developing formulations of plant latex.

Impact of black cherry on pedunculate oak vitality in mixed forests:Balancing benefits and concerns

The vitality of European forests continues to decline due to new pests and diseases,climate-change related disturbances and high loads of atmospheric nitrogen deposition.Deteriorating soil health is a major factor underpinning the low vitality of West-European forests.Selecting tree species with soil ameliorative traits is proposed as an avenue to counteract soil acidification and improve overall forest vitality.Here we evaluate the impact of black cherry(Prunus serotina Ehrh.),a known rich litter species,on the vitality of neighboring pedunculate oak(Quercus robur L.)in ten mixed forests on sand in Germany,Belgium and the Netherlands.We found that black cherry admixture increases foliar N and P to a surplus whereas it causes deficiencies in foliar Mg,thereby resulting in an overall negative effect on oak foliar nutrient concentrations.Contrary,defoliation of oak leaves by herbivory decreases with the proximity of black cherry.Using structural equation modelling(SEM),we tested the hypothesized‘improved soil health’pathway.Our analyses showed that black cherry admixture leads to lower accumulation in the humus layer,resulting in higher soil base saturation which has a positive effect on foliar Ca yet a negative effect on total chlorophyll.Moreover,the SEM illustrated that herbivory of oak leaves decreases when black cherry is admixed,both via dilution and improved soil health.Indirect effects of black cherry on oak vitality via“improved soil health”in our SEM are however small in comparison to direct relations.Hence,our study showed that the combined positive and negative impacts of black cherry on oak vitality are limited,which tempers the potential benefits of using the rich litter species to counteract oak decline via improved soil health–yet,the concern of black cherry as an invasive alien species negatively affecting the vitality of mature pedunculate oak trees may also be exaggerated.

Global Change Effects on Plant Chemical Defenses against Insect Herbivores

This review focuses on individual effects of major global change factors, such as elevated CO2, O3, UV light and temperature, on plant secondary chemistry. These secondary metabolites are well-known for their role in plant defense against insect herbivory. Global change effects on secondary chemicals appear to be plant species-specifc and dependent on the chemical type. Even though plant chemical responses induced by these factors are highly variable, there seems to be some specificity in the response to different environmental stressors. For example, even though the production of phenolic compounds is enhanced by both elevated CO2 and UV light levels, the latter appears to primarily increase the concentrations of flavonoids. Likewise, specific phenolic metabolites seem to be induced by O3 but not by other factors, and an increase in volatile organic compounds has been particularly detected under elevated temperature. More information is needed regarding how global change factors influence inducibility of plant chemical defenses as well as how their indirect and direct effects impact insect performance and behavior, herbivory rates and pathogen attack. This knowledge is crucial to better understand how plants and their associated natural enemies will be affected in future changing environments.

A novel herbivorous wood-borer insect outbreak triggers die-offs of a foundation plant species in coastal ecosystems

Introduction:Understanding the trophic interactions between plants and herbivorous insects is essential for managing the ecosystem health and sustainability in the context of climate change and anthropogenic disturbance.The Tamarix chinensis is a foundation plant species of salt marshes in northern China,which provides a variety of ecological functions and services in coastal ecosystems such as withstanding storm tide,conserving biodiversity,and preventing shoreline erosion.Outcomes:However,through long-term field observations,for the first time,we found that the health of this population has been suffering from the potential outbreak of a novel wood-borer insect(Zeuzera leuconotum Butler)under multiple stresses,contributing substantially to the degradation of the coastal salt marshes.Discussion and Conclusion:Therefore,there is urgent need and great significance to investigate the potential impact of this herbivorous wood-borer insects on health and sustainability of plant community in coastal ecosystems for in-depth understanding its degradation mechanisms.

Poleward increase in feeding efficiency of leafminer Stigmella lapponica(Lepidoptera:Nepticulidae)in a latitudinal gradient crossing a boreal forest zone

Damage to plant communities imposed by insect herbivores generally decreases from low to high latitudes.This decrease is routinely attributed to declines in herbivore abundance and/or diversity,whereas latitudinal changes in per capita food consumption remain virtually unknown.Here,we tested the hypothesis that the lifetime food consumption by a herbivore individual decreases from low to high latitudes due to a temperature-driven decrease in metabolic expenses.From 2016 to 2019,we explored latitudinal changes in multiple characteristics of linear(gallery)mines made by larvae of the pygmy moth,Stigmella lapponica,in leaves of downy birch,Betula pubescens.The mined leaves were larger than intact leaves at the southern end of our latitudinal gradient(at 60°N)but smaller than intact leaves at its northern end(at 69°N),suggesting that female oviposition preference changes with latitude.No latitudinal changes were observed in larval size,mine length or area,and in per capita food consumption,but the larval feeding efficiency(quantified as the ratio between larval size and mine size)increased with latitude.Consequently,S.lapponica larvae consumed less foliar biomass at higher latitudes than at lower latitudes to reach the same size.Based on space-for-time substitution,we suggest that climate warming will increase metabolic expenses of insect herbivores with uncertain consequences for plant-herbivore interactions.

Grasshoppers （Orthoptera： Acrididae） select vegetation patches in local-scale responses to foliar nitrogen but not phosphorus in native grassland

Key elements such as nitrogen （N） and phosphorus （P） are often limiting relative to the nutritional needs of herbivores that feed on them. While N often limits insect herbivores in natural terrestrial ecosystems, the effect of P is poorly studied in the field, even though compelling hypotheses from the ecological stoichiometry literature predict its importance. We evaluated small-scale spatial distributions of, and herbivory by, grasshoppers among neighboring plots that vary in foliar-N and -P in tallgrass prairie. Grasshopper densities were 67% greater in N-fertilized plots but detected no effect to grasshopper densities from P-fertilizer. Leaf damage to the dominant grass Andropogon gerardii was 32% greater in N-fertilized plots, but no response to foliar-P was detected. Herbivore damage to a common forb, goldenrod （Solidago missouriensis）, was not strongly linked by fertilizer treatments, although there was increased leaf damage in N-fertilizer treatments when no P was applied （a significant N ~ P interaction）. Under field conditions at local scales, we conclude that spatially heterogeneous distributions of grasshoppers are primarily affected by foliar-N in host plants with little evidence that P-levels contribute to the spatial patterns.