Phytophagous insect-woody sprout interactions in tropical eucalypt forest. I. Insect herbivory

Abstract Foliar insect damage levels on woody sprouts in the ground layer of two tropical eucalypt forest communities on Melville Island were between 7.8 and 43.2%. Of eight common tree species, Eucalyptus confertiflora was damaged most by insects and Buchanania obovata and Terminalia ferdinandiana the least. Seasonal trends in insect damage were not consistent between plant species and were not always consistent between vegetation types for a particular plant species. The results of this study are not consistent with hypotheses suggesting that insect grazing is a critical determinant of tree species dominance or woody sprout dormancy.     

昆虫植食对植物有性生殖的影响

植物在个体发育的各个阶段都与不同的群落成员相互作用,如竞争的植物、有益的传粉者和敌对的植食动物。昆虫植食在各类生态系统中普遍存在,并可能对植物有性生殖产生各种影响。植食昆虫可通过对植物有性生殖结构的消耗直接对植物生殖产生影响,也可通过影响植物资源分配和花性状等改变传粉者服务,从而间接对植物有性生殖带来正面、负面或中性的影响。同一植物的植食昆虫和传粉者往往对植物的吸引性状 （如花大小、气味、颜色等）有相同的偏好,因此植食者与传粉者均能对植物有性生殖性状施加选择压力。本文从昆虫植食对植物有性生殖的直接影响、间接影响以及植食昆虫对植物有性生殖性状选择的影响三个方面进行综述,以期为昆虫植食和生物资源多样性保护相关研究提供参考。     

Potential impacts of climate change on patterns of insect herbivory on understorey plant species: A transplant experiment

Species‐specific responses to climate change will lead to changes in species interactions across multiple trophic levels. Interactions between plants and their insect herbivores, in particular, may become increasingly disrupted if mobile herbivores respond more rapidly to climatic change than their associated host plants. We present a multispecies transplant experiment aimed at assessing potential climatic impacts on patterns of leaf herbivory. Four shrubby understorey plant species were transplanted outside their native range into a climate 2.5°C warmer in annual mean temperature. After 12 months, we assessed the types and amount of herbivore leaf damage, compared with plants transplanted to a control site within their native range. The overall amount of foliage loss to herbivores ranged from approximately 3–10% across species and sites, a range consistent with most estimates of leaf loss in other studies. The most common types of leaf damage were sucking and chewing and this pattern was consistent for all four plant species at all sites. There were no significant differences in levels and patterns of herbivory between control and warm sites for three out of four plant species. This suggests that with moderate climate warming, most herbivory will continue to be dominated by chewers and suckers, and that the overall level of foliage loss will be similar to that experienced presently.     

Regional and local variation in insect herbivory,vegetation and soils of eucalypt associations in contrasted landscape positions along a climatic gradient

Abstract Relationships with climate and local resources are developed for soils, vegetation and tree foliage as well as levels of herbivory for the dominant eucalypts at sites representing a regional gradient in climate and local contrasts in landscape position. Indicators of site productivity such as soil nitrogen and phosphorus, canopy height and cover, foliar nitrogen and water, and average leaf area tended to increase as climate became more favourable. Many were also higher in locally richer parts of the landscape. In contrast, specific leaf weight, an indication of sclerophylly, decreased as climate and local resources became more favourable. Rates of herbivory tended to increase with increasing site productivity and the associated changes in soil, vegetation and foliar properties, in broad agreement with models relating herbivory to resource availability and plant vigour. We found no evidence to support models relating high herbivory to low-resource environments and plant stress. The apparent level of herbivore damage on mature leaves was highest at intermediate levels of resources; this could reflect interactions between resource availability, rates of herbivory and rates of leaf replacement. Implications of these findings are discussed with respect to ways of measuring herbivory, regional patterns in rates and levels of herbivory, and the regional distribution of rural dieback associated with high herbivory.     

上海地区葡萄种植园昆虫种群调查

葡萄是上海地区重要的经济水果,为探明上海葡萄种植园中昆虫种群组成,本研究在2017-2018年间,通过搜捕法、马氏网诱集法和黄色粘纸诱集法,对上海市嘉定区、奉贤区、青浦区、浦东新区、崇明岛进行了昆虫种群调查,共采集并鉴定昆虫7目65科123属182种,明确了上海地区葡萄种植园内主要害虫、天敌昆虫及环境昆虫的种类,并对上海葡萄园的昆虫种群结构和多样性进行了分析。     

模拟昆虫取食对牛膝菊防御特征的影响

为了解入侵植物牛膝菊的入侵机理,研究其应对昆虫取食的响应,在开花前喷洒不同浓度(5、10、20 mmol·L-1)的茉莉酸甲酯(MeJA)来模拟不同程度的昆虫取食,试验结束时测定其株高、叶片数、花序数、生物量、比叶面积、叶上表皮毛密度,以及叶和花序中的缩合单宁、总酚、黄酮含量.结果表明:5 mmol·L-1 MeJA处...     

Consequences of insect herbivory on grape fine root systems with different growth rates

Herbivory tolerance has been linked to plant growth rate where plants with fast growth rates are hypothesized to be more tolerant of herbivory than slower-growing plants. Evidence supporting this theory has been taken primarily from observations of aboveground organs but rarely from roots. Grapevines differing in overall rates of new root production, were studied in Napa Valley, California over two growing seasons in an established vineyard infested with the sucking insect, grape phylloxera (Daktulosphaira vitifoliae Fitch). The experimental vineyard allowed for the comparison of two root systems that differed in rates of new root tip production (a 'fast grower', Vitis berlandieri x Vitis rupestris cv. 1103P, and a slower-growing stock, Vitis riparia x Vitis rupestris cv. 101-14 Mgt). Each root system was grafted with a genetically identical shoot system (Vitis vinifera cv. Merlot). Using minirhizotrons, we did not observe any evidence of spatial or temporal avoidance of insect populations by root growth. Insect infestations were abundant throughout the soil profile, and seasonal peaks in phylloxera populations generally closely followed peaks in new root production. Our data supported the hypothesis that insect infestation was proportional to the number of growing tips, as indicated by similar per cent infestation in spite of a threefold difference in root tip production. In addition, infested roots of the fast-growing rootstock exhibited somewhat shorter median lifespans (60 d) than the slower-growing rootstock (85 d). Lifespans of uninfested roots were similar for the two rootstocks (200 d). As a consequence of greater root mortality of younger roots, infested root populations in the fast-growing rootstock had an older age structure. While there does not seem to be a trade-off between potential growth rate and relative rate of root infestation in these cultivars, our study indicates that a fast-growing root system may more readily shed infested roots that are presumably less effective in water and nutrient uptake. Thus, differences in root tip production may be linked to differences in the way plants cope with roots that are infested by sucking insects.     

Simulated herbivory does not constrain phenotypic plasticity to shade through ontogeny in a relict tree

Ecological limits to phenotypic plasticity (PP), induced by simultaneous biotic and abiotic factors, can prevent organisms from exhibiting optimal plasticity, and in turn lead to decreased fitness. Herbivory is an important biotic stressor and may limit plant functional responses to challenging environmental conditions such as shading. In this study we investigated whether plant functional responses and PP to shade are constrained by herbivory, and whether such constraints are due to direct effects based on resource limitation by considering ontogeny. We used as a model system the relict tree Prunus lusitanica and implemented an indoor experiment to quantify the response of saplings of different ages to shade and herbivory. We measured five functional traits and quantitatively calculated PP. Results showed that herbivory did not constrain functional responses or PP to shade except for shoot:root ratio (SR), which, despite showing a high PP in damaged saplings, decreased under shade instead of increasing. Damaged saplings of older age did not exhibit reduced constraints on functional responses to shade and generally presented a lower PP than damaged saplings of younger age. Our findings suggest that herbivory‐mediated constraints on plant plasticity to shade may not be as widespread as previously thought. Nonetheless, the negative effect of herbivory on SR plastic expression to shade could be detrimental for plant fitness. Finally, our results suggest a secondary role of direct effects (resource‐based) on P. lusitanica plasticity limitation. Further studies should quantify plant resources in order to gain a better understanding of this seldom‐explored subject.     

Global patterns of insect herbivory in gap and understorey environments,and their implications for woody plant carbon storage

Insect herbivory is thought to favour carbon allocation to storage in juveniles of shade‐tolerant trees. This argument assumes that insect herbivory in the understorey is sufficiently intense as to select for storage; however, understoreys might be less attractive to insect herbivores than canopy gaps, because of low resource availability and – at temperate latitudes – low temperatures. Although empirical studies show that shade‐tolerant species in tropical forests do allocate more photosynthate to storage than their light‐demanding associates, the same pattern has not been consistently observed in temperate forests. Does this reflect a latitudinal trend in the relative activity of insect herbivory in gap versus understorey environments? To date there has been no global review of the effect of light environment on insect herbivory in forests. We postulated that if temperature is the primary factor limiting insect herbivory, the effect of gaps on rates of insect herbivory should be more evident in temperate than in tropical forests; due to low growing season temperatures in the oceanic temperate forests of the Southern Hemisphere, the effect of gaps on insect herbivory rates should in turn be stronger there than in the more continental temperate climates of the Northern Hemisphere. We examined global patterns of insect herbivory in gaps versus understories through meta‐analysis of 87 conspecific comparisons of leaf damage in contrasting light environments. Overall, insect herbivory in gaps was significantly higher than in the understorey; insect herbivory was 50% higher in gaps than in understoreys of tropical forests but did not differ significantly between gaps and understories in temperate forests of either hemisphere. Results are consistent with the idea that low resource availability – and not temperature – limits insect herbivore activity in forest understoreys, especially in the tropics, and suggest the selective influence of insect herbivory on late‐successional tree species may have been over‐estimated.     

两种不同种植方式对龙葵叶片虫食状的影响研究

昆虫与植被之间相互关系的深入研究,有助于更好的理解生态系统结构与功能之间的关系以及生态系统生物多样性维持机理。本文通过对集中种植和分块种植下两种不同种植方式龙葵叶片虫食状进行调查分析,以期对龙葵的栽培和养护提供理论基础和技术建议。研究结果表明:龙葵叶片中共识别出11种虫食状类型,其中,集中种植方式有10种,分块种植方式有11种,各种虫食状类型出现频率在0.4%-24.7%;集中种植样地的龙葵叶片虫食状种类数、Shannon-Wiener指数和Pielou均匀度指数均低于分块种植;分块种植的龙葵叶片受到植食性昆虫的伤害频率较高,但是集中种植的龙葵叶片受到的伤害程度却明显高于分块种植方式。因此,种植龙葵应尽量避免大规模集中种植方式,不同生态系统边界之间边缘效应的尺度和强弱的关系是未来研究的重点和核心问题。     

The ecology of predispersal insect herbivory on tree reproductive structures in natural forest ecosystems

Plant-insect interactions are key model systems to assess how some species affect the distribution, the abundance, and the evolution of others. Tree reproductive structures represent a critical resource for many insect species, which can be likely drivers of demography, spatial distribution, and trait diversification of plants. In this review, we present the ecological implications of predispersal herbivory on tree reproductive structures by insects (PIHR) in forest ecosystems. Both insect's and tree's perspectives are addressed with an emphasis on how spatiotemporal variation and unpredictability in seed availability can shape such particular plant-animal interactions. Reproductive structure insects show strong trophic specialization and guild diversification. Insects evolved host selection and spatiotemporal dispersal strategies in response to variable and unpredictable abundance of reproductive structures in both space and time. If PIHR patterns have been well documented in numerous systems, evidences of the subsequent demographic and evolutionary impacts on tree populations are still constrained by time-scale challenges of experimenting on such long-lived organisms, and modeling approaches of tree dynamics rarely consider PIHR when including biotic interactions in their processes. We suggest that spatially explicit and mechanistic approaches of the interactions between individual tree fecundity and in sect dynamics will clarify predictions of the demogenetic implications of PIHR in tree populations. In a global change context, further experimental and theoretical contributions to the likelihood of life-cycle disruptions between plants and their specialized herbivores, and to how these changes may gen erate novel dynamic patterns in each partner of the interaction are increasingly critical.     

Leaf traits and herbivory rates of tropical tree species differing in successional status

We evaluated leaf characteristics and herbivory intensities for saplings of fifteen tropical tree species differing in their successional position. Eight leaf traits were selected, related to the costs of leaf display (specific leaf area [SLA], water content), photosynthesis (N and P concentration per unit mass), and herbivory defence (lignin concentration, C:N ratio). We hypothesised that species traits are shaped by variation in abiotic and biotic (herbivory) selection pressures along the successional gradient. All leaf traits varied with the successional position of the species. The SLA, water content and nutrient concentration decreased, and lignin concentration increased with the successional position. Herbivory damage (defined as the percentage of damage found at one moment in time) varied from 0.9-8.5% among the species, but was not related to their successional position. Herbivory damage appeared to be a poor estimator of the herbivory rate experienced by species, due to the confounding effect of leaf lifespan. Herbivory rate (defined as percentage leaf area removal per unit time) declined with the successional position of the species. Herbivory rate was only positively correlated to water content, and negatively correlated to lignin concentration, suggesting that herbivores select leaves based upon their digestibility rather than upon their nutritive value. Surprisingly, most species traits change linearly with succession, while resource availability (light, nutrients) declines exponentially with succession.     

The constraints of selecting for insect resistance in plantation trees

• 1 High productivity in plantations of exotic tree species is achieved by management for fast growth in the absence of the full complex of co‐evolved insect herbivores. In the case of Eucalyptus, silvicultural selection for desirable wood traits is concomitant with a trade‐off against defence and a reduction of chemical and genetic diversity. These factors, combined with accidental introductions, rapid insect evolution and the emergence of new pests, increase the likelihood that future plantations will need insect pest management to maintain productivity.
• 2 Forestry researchers have suggested that selecting for resistant genotypes may be beneficial in insect control. There are, however, significant differences between long‐lived trees and annual crops that make this approach unlikely to be successful. This is illustrated using several examples of research into resistance to insect herbivores in trees.
• 3 Selection for resistance to insects in trees requires an assessment of trial plantations for heritable variation in insect damage and then a determination of the effect of variation in resistance on insect population parameters. Identifying rare resistant genotypes using markers is difficult because many factors interact to produce a resistant phenotype, and phytophagous insects have less intimate relationships with their host than pathogens, resulting in weak associations with genetic loci.
• 4 If resistant genotypes are identified, their widespread deployment in plantations might not provide satisfactory management of insect pests when the use of extensive monocultures is continued. In this paper, experiments are suggested that would explore the effectiveness of polycultures or chemotype mixtures with respect to ameliorating the damage of insects on plantation productivity. In addition, mitigating the effects of some insects on plantation productivity by maintaining vigour of fast‐growing eucalypts should be considered.

     

Influence of previous frost damage on tree growth and insect herbivory of Eucalyptus globulus globulus

The plant stress hypothesis suggests that some herbivores favour stressed plants, whereas the plant vigour hypothesis proposes that other herbivores prefer vigorous plants. The effects of a prior stress, that of frost damage, were examined on the subsequent growth of Eucalyptus globulus globulus and on the response of insect herbivores. Frost damage affected tree growth by reducing new leaf area and increasing specific leaf area (SLA). However, herbivore abundance was not affected by prior frost damage. Two feeding trials using Anoplognathus chloropyrus and Hyalarcta huebneri and a morphometric study of Ctenarytaina eucalypti were conducted to assess the performance of herbivores on trees that had suffered more or less frost damage. Consumption by A. chloropyrus and H. huebneri was unaffected by foliage origin (damaged versus healthy). Hyalarcta huebneri grew faster when fed leaves from previously damaged trees, and C. eucalypti from previously damaged trees were larger than those from healthy trees. Enhanced insect performance on frost damaged plants may have resulted from the high specific leaf area (most likely thinner) leaves. The herbivore abundance data did not support the hypothesis that previously frost damaged plants are preferred by insects. However, increased growth of H. huebneri and larger body size of C. eucalypti on damaged trees indicates that previously stressed trees may produce leaves of higher nutritional value.     

Weak latitudinal gradients in insect herbivory for dominant rangeland grasses of North America

Patterns of insect herbivory may follow predictable geographical gradients, with greater herbivory at low latitudes. However, biogeographic studies of insect herbivory often do not account for multiple abiotic factors (e.g., precipitation and soil nutrients) that could underlie gradients. We tested for latitudinal clines in insect herbivory as well as climatic, edaphic, and trait‐based drivers of herbivory. We quantified herbivory on five dominant grass species over 23 sites across the Great Plains, USA. We examined the importance of climate, edaphic factors, and traits as correlates of herbivory. Herbivory increased at low latitudes when all grass species were analyzed together and for two grass species individually, while two other grasses trended in this direction. Higher precipitation was related to more herbivory for two species but less herbivory for a different species, while higher specific root length was related to more herbivory for one species and less herbivory for a different species. Taken together, results highlight that climate and trait‐based correlates of herbivory can be highly contextual and species‐specific. Patterns of insect herbivory on dominant grasses support the hypothesis that herbivory increases toward lower latitudes, though weakly, and indicates that climate change may have species‐specific effects on plant–herbivore interactions.     

Additive and nonadditive effects of herbivory and competition on tree seedling mortality, growth, and allocation

The interaction between simulated cotyledon herbivory and interspecific competition was studied in a greenhouse experiment using two species of trees, Acer rubrum and Quercus palustris, which commonly invade abandoned agricultural fields. Herbivory treatments were applied as a gradient of cotyledon removal for A. rubrum with 0, 25, 50, 75, and 100% of cotyledon tissue removed. Cotyledons from Q. palustris were clipped and removed (control, early, and late removal) to create a gradient of seed reserve availability. The competition treatment consisted of plugs of old-field vegetation that filled the pots with perennial cover. Mortality of seedlings was higher with competition. There was a significant interaction between herbivory and competition with the highest mortality occurring with competition at the highest intensity of herbivory in both species. Herbivory reduced biomass for Q. palustris only, while competition reduced biomass in both species. Neither species showed an interaction between herbivory and competition for growth. There was a significant interaction between herbivory and competition on allocation patterns for both species, with greater allocation to roots with competition at the highest intensity of herbivory. This study demonstrates the potential for cotyledon herbivory and competition to interact, altering the invasion of tree seedlings into abandoned agricultural land.     

植物竞争和昆虫取食调节入侵植物对土壤细菌群落和功能的影响

以入侵植物空心莲子草(Alternanthera philoxeroides(Mart.)Griseb)、本土近缘种莲子草(Alternan-thera sessilis(L.)DC)、生防昆虫莲草直胸跳甲(Agasicles hygrophila(Selman&Vogt))和本地昆虫虾钳菜披龟甲(Cassida pi...