Potential host colonization by insect herbivores in a warmer climate: a transplant experiment

We conducted a transplant experiment to investigate the potential colonization of a plant species by insect herbivores under a warmer climate. Acacia falcata seeds collected from four latitudes, encompassing the current coastal range of the species (1150 km), were grown in the same soil type and climatic conditions in a glasshouse. Plants were then transplanted to two sites, 280 km north of A. falcata's current coastal range; the transplant sites were 1.2 and 5.5°C warmer than the northernmost and southernmost boundaries of the species' current range, respectively. We compared the structure and composition of the herbivorous Hemiptera and Coleoptera communities on the transplants (i) to that of A. falcata within its current distribution, (ii) to a closely related Acacia species (Acacia leptostachya) that naturally occurred at the transplant sites, and (iii) among the A. falcata transplants originating from seeds collected at different latitudes. Herbivory on A. falcata was also compared between the transplants and the current distribution, and among transplant originating from different latitudes. Thirty species of externally feeding herbivorous Coleoptera and Hemiptera were collected from the transplanted A. falcata over a period of 12 months following transplantation. Guild structure of this herbivore community (based on the proportion of species within each of seven groups based on taxonomy and feeding style) did not significantly differ between the transplants and that found on A. falcata within its natural range, but did differ between the transplants and A. leptostachya. Rates of herbivory did not significantly differ between the transplants and plants at sites within the natural range. There were no significant differences in herbivore species richness or overall rates of herbivory on the transplants originating from different latitudes. In conclusion, host plant identity was apparently more important than climate in influencing the structure of the colonizing herbivore community. If this result holds for other plant–herbivore systems, we might expect that under a warmer climate, broad patterns in insect community structure and rates of herbivory may remain similar to that at present, even though species composition may change substantially.     

Community structure of insect herbivores on introduced and native Solidago plants in Japan

We compared community composition, density, and species richness of herbivorous insects on the introduced plant Solidago altissima L. (Asteraceae) and the related native species Solidago virgaurea L. in Japan. We found large differences in community composition on the two Solidago species. Five hemipteran sap feeders were found only on S. altissima. Two of them, the aphid Uroleucon nigrotuberculatum Olive (Hemiptera: Aphididae) and the scale insect Parasaissetia nigra Nietner (Hemiptera: Coccidae), were exotic species, accounting for 62% of the total individuals on S. altissima. These exotic sap feeders mostly determined the difference of community composition on the two plant species. In contrast, the herbivore community on S. virgaurea consisted predominately of five native insects: two lepidopteran leaf chewers and three dipteran leaf miners. Overall species richness did not differ between the plants because the increased species richness of sap feeders was offset by the decreased richness of leaf chewers and leaf miners on S. altissima. The overall density of herbivorous insects was higher on S. altissima than on S. virgaurea, because of the high density of the two exotic sap feeding species on S. altissima. We discuss the importance of analyzing community composition in terms of feeding guilds of insect herbivores for understanding how communities of insect herbivores are organized on introduced plants in novel habitats.     

Effects of environmental factors on the species composition of aquatic insects in irrigation ponds

Although irrigation ponds contribute to the conservation of aquatic biodiversity, they have experienced declines in recent years. We therefore examined the relationships between various environmental factors and the community composition of aquatic insects, specifically insect predators, in irrigation ponds to gain knowledge that would aid in the conservation and restoration of biodiversity. We selected Odonata, Hemiptera and Coleoptera as target taxonomic groups and conducted censuses of these groups in 21 ponds in Shiga, central Japan. In total, we collected 30 and 10 species (or species groups) of Odonata and Hemiptera, respectively, and 17 species of Coleoptera. A partial canonical correspondence analysis revealed that the following four environmental factors significantly affected the species composition of aquatic insect communities: the number of emergent plant species, percent concrete revetment, presence of litter and peripheral length. Among these variables, the number of emergent plant species was the most potent factor, perhaps because emergent plants serve as sites for oviposition and emergence, and provide refugia for aquatic insects (odonate nymphs in particular). In contrast, some species specifically inhabited sites poor in emergent plants. This study shows that reductions in concrete revetments are necessary for the conservation of biodiversity. This would lead to increases in the number of aquatic plant species, which provide habitats and oviposition sites for many aquatic insects. Furthermore, to enrich the local biodiversity of aquatic insects, groups of irrigation ponds with different environments are needed.     

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.     

Plant-Feeding Hemiptera and Orthoptera Communities in Native and Restored Mesic Tallgrass Prairies

Aboveground Hemiptera and Orthoptera communities were compared among three native and three restored mesic tallgrass prairies along the Platte River in central Nebraska to assess both the relative success of restored sites and the relationship between insect and plant communities. Hemiptera and Orthoptera were sampled using sweep nets in early June, mid-July, and mid-August 2000. Plant species composition was assessed in early June and mid-August. A total of 89 Auchenorrhyncha (71 Cicadellidae, 15 Fulgoroidea, and 3 Membracidae) and 23 orthopterans (15 Acrididae and 8 Tettigoniidae) were collected. Eighty-five plant species were observed in combined study sites. Shannon diversity was significantly higher at restored prairie for Cicadellidae ( H '= 1.38), Fulgoroidea ( H '= 0.796), and Membracidae ( H '= 0.290), which comprised the majority of individual insects collected, but significantly higher at native prairie for Acrididae ( H '= 0.560) and Tettigoniidae ( H '= 0.480) ( p ≤ 0.05). Species richness was comparable except for Acrididae which were significantly higher in restored prairie. Density of insects generally followed species diversity but was only significantly higher in restored areas for Membracidae. The number of remnant-dependent species collected was comparable for both native prairie ( n = 15) and restored prairie ( n = 15). These results suggest that, at least for Hemiptera, differences in insect communities between native and restored prairie may best be explained by the presence of insect host plants rather than by whether a site is native or restored.     

Diversity and abundance patterns of phytophagous insect communities on alien and native host plants in the Brassicaceae

The herbivore load (abundance and species richness of herbivores) on alien plants is supposed to be one of the keys to understand the invasiveness of species. We investigate the phytophagous insect communities on cabbage plants (Brassicaceae) in Europe. We compare the communities of endophagous and ectophagous insects as well as of Coleoptera and Lepidoptera on native and alien cabbage plant species. Contrary to many other reports, we found no differences in the herbivore load between native and alien hosts. The majority of insect species attacked alien as well as native hosts. Across insect species, there was no difference in the patterns of host range on native and on alien hosts. Likewise the similarity of insect communities across pairs of host species was not different between natives and aliens. We conclude that the general similarity in the community patterns between native and alien cabbage plant species are due to the chemical characteristics of this plant family. All cabbage plants share glucosinolates. This may facilitate host switches from natives to aliens. Hence the presence of native congeners may influence invasiveness of alien plants.     

Diversity and guild structure of insect assemblages under grazing and exclusion regimes in a montane grassland from Central Argentina

The effects of grazing disturbance on insect communities were examined at a montane grassland in Central Argentina, by comparing two grazed sites differing in cattle load (heavy and continuous or moderate and discontinuous) and two cattle exclusions differing in age (7 and 19 years). Two aspects of insect diversity (taxonomic and guild structure) and two levels of taxonomic resolution (family and species) were considered. Four monthly samples were taken with a suction sampler in two 1 m² areas at each site. Collected specimens were counted, identified to family (all insects) or species (Coleoptera) level, and allocated to trophic guilds. Abundance, richness, diversity and biomass of the insect assemblages had minimum values in the most intensely grazed habitat, which also differed from the other sites in terms of insect families and Coleoptera species composition. It also showed a distinct guild structure, with fewer secondary consumers, and chewers replacing suckers as the most abundant herbivore group. According to these observations, intense grazing in montane grasslands in Central Argentina could result in taxonomic and guild changes in the associated insect communities, but such effects would not be noticeable with less intensive use. Moreover, using family taxonomic level could be as or even more appropriate than species level in order to characterize insect communities in the studied habitats under varying disturbance regimes.     

Not all non‐natives are equally unequal: reductions in herbivore β‐diversity depend on phylogenetic similarity to native plant community

Effects of host plant α‐ and β‐diversity often confound studies of herbivore β‐diversity, hindering our ability to predict the full impact of non‐native plants on herbivores. Here, while controlling host plant diversity, we examined variation in herbivore communities between native and non‐native plants, focusing on how plant relatedness and spatial scale alter the result. We found lower absolute magnitudes of β‐diversity among tree species and among sites on non‐natives in all comparisons. However, lower relative β‐diversity only occurred for immature herbivores on phylogenetically distinct non‐natives vs. natives. Locally in that comparison, non‐native gardens had lower host specificity; while among sites, the herbivores supported were a redundant subset of species on natives. Therefore, when phylogenetically distinct non‐natives replace native plants, the community of immature herbivores is likely to be homogenised across landscapes. Differences in communities on closely related non‐natives were subtler, but displayed community shifts and increased generalisation on non‐natives within certain feeding guilds.     

The Hemiptera (Insecta) communities of tropical rain forest in Sulawesi

The structure and composition of Hemiptera communities of tropical rain forest in Dumoga-Bone National Park, Sulawesi, Indonesia were investigated over a 1-year period. The aim was to investigate the extent to which insect samples, obtained using six different techniques, were representative of the whole community, and to explore temporal and spatial variation in Hemiptera community composition. Sampling techniques employed were Rothamsted light trapping, canopy fogging, malaise trapping at both ground and canopy level, flight interception trapping and yellow water pan trapping. Overlap between faunas collected using different techniques was surprisingly low emphasizing the limitations of using any single method to sample and thereby describe the Hemiptera community. Differences were observed at the species, family and suborder levels. Similarly, there were major differences in faunal composition between sites and diversity appeared to peak at elevations between 600–1000 m. Seasonal changes were also significant but generally lower than between methods or sites. Results are discussed in relation to factors such as food availability and host specialization and the efficacy of each sampling method is reviewed in relation to the biology of the different Hemiptera groups and the composition of the samples obtained.     

Recipient Environment More Important than Community Composition in Determining the Success of an Experimental Sponge Transplant

Human activities have inflicted profound damage upon many ecosystems, and ecologists are now seeking effective means of restoring ecosystems to their natural state. Industrial ports and harbors are highly modified and often depauperate in native fauna. They are typically characterized by poor water quality and modified community composition, both of which may hinder attempts to reintroduce native species. Here, we conducted a field experiment to separate the effects of the recipient environment and community composition on the success of endemic sponge explants in Port Kembla Harbor, NSW, Australia. A reciprocal transplant was conducted between communities originating from six sites that varied in water quality and community composition, enabling us to assess the relative factors simultaneously. A colony of the endemic sponge Tedania anhelans was then inserted into the center of each community, and we quantified the survival, growth, and metal bioaccumulation of sponges over three months. Endemic sponges consistently performed better against resident assemblages when water quality was good. Sponges transplanted to cleaner sites had over double the survivorship and approximately three times the surface area of sponges transplanted to disturbed sites. These patterns were independent of community composition. Bioaccumulation of metals in sponges was correlated with survival; however, other factors such as turbidity may be required to explain sponge mortality at some sites. This study adds to evidence that remediation of the physical and chemical environments may be a prerequisite for biological remediation and demonstrates the value of experimental transplants in assessing restoration potential.     

Diversity and assemblage structure of phytophagous Hemiptera along a latitudinal gradient: predicting the potential impacts of climate change

Aims The aims were (1) to assess the species richness and structure of phytophagous Hemiptera communities along a latitudinal gradient, (2) to identify the importance of rare species in structuring these patterns, and (3) to hypothesize about how phytophagous Hemiptera communities may respond to future climate change. Location East coast of Australia. Methods Four latitudes within the 1150 km coastal distribution of Acacia falcata were selected. The insect assemblage on the host plant Acacia falcata was sampled seasonally over two years. Congeneric plant species were also sampled at the sites. Results Ninety‐eight species of phytophagous Hemiptera were collected from A. falcata. Total species richness was significantly lower at the most temperate latitude compared to the three more tropical latitudes. We classified species into four climate change response groups depending on their latitudinal range and apparent host specificity. Pairwise comparisons between groups showed that the cosmopolitan, generalist feeders and specialists had a similar community structure to each other, but the climate generalists had a significantly different structure. Fifty‐seven species were identified as rare. Most of these rare species were phloem hoppers and their removal from the dataset led to changes in the proportional representation of all guilds in two groups: the specialist and generalist feeders. Main conclusions We found no directional increase in phytophagous Hemiptera species richness. This indicates that, at least in the short term, species richness patterns of these communities may be similar to that found today. As the climate continues to change, however, we might expect some increases in species richness at the more temperate latitudes as species migrate in response to shifting climate zones. In the longer term, more substantial changes in community composition will be expected because the rare species, which comprise a large fraction of these communities, will be vulnerable to both direct climatic changes, and indirect effects via changes to their host's distribution.     

Canopy invertebrate community composition on rainforest trees: Different microhabitats support very different invertebrate communities

Tropical rainforest canopies are renowned for their high invertebrate diversity and abundance. The canopy comprises a range of microhabitats representing very different food resources (including photosynthetic, reproductive, and structural tissues). As these resources vary considerably in temporal and spatial availability, nutritional quality, chemical protection and other attributes, we hypothesized that microhabitats support structurally different invertebrate communities. To test this we used the Australian Canopy Crane to sample invertebrates from mature leaves, flush leaves, flowers, fruit and suspended dead wood from 23 plant species. Invertebrate faunas on different microhabitats varied in taxonomic composition and feeding guild structure in support of the microhabitat differentiation hypothesis. Herbivores were found predominantly on new leaves (Hemiptera, Lepidoptera) and especially flowers (Coleoptera, Thysanoptera), but were relatively uncommon on mature leaves. Instead, the mature foliage community was dominated by predators, especially spiders and ants, and supported high abundances of saprophages. Ripe fruit and dead wood were scarce canopy resources that were utilized by a relatively small number of invertebrates, mostly saprophages and fungivores. Flowers supported a more heterogeneous fauna than the leaves in terms of proportional abundances of taxonomic groups and feeding guilds, both within tree species (evenness) and between tree species (non‐uniformity). These results demonstrate microhabitat differentiation in a rainforest canopy and are the first to quantify differences in taxonomic composition, guild structure and abundance patterns between such diverse invertebrate assemblages within host trees. We conclude that studies based only on sampling one microhabitat, and leaves in particular, may provide a distorted picture of invertebrate community structure.     

Evolutionary responses of native plants to novel community members

Both ecological and evolutionary processes can influence community assembly and stability, and native community members may respond both ecologically and evolutionarily as additional species enter established communities. Biological invasions provide a unique opportunity to examine these responses of native community members to novel species additions. Here, I use reciprocal transplant experiments among naturally invaded and uninvaded environments, along with experimental removals of exotic species, to determine whether exotic plant competitors and exotic insect herbivores evoke evolutionary changes in native plants. Specifically, I address whether the common native plant species Lotus wrangelianus has responded evolutionarily to a series of biological invasions by adapting to the presence of the exotic plant Medicago polymorpha and the exotic insect herbivore Hypera brunneipennis. Despite differences in selection regimes between invaded and uninvaded environments and the presence of genetic variation for traits relevant to the novel competitive and plant-herbivore interactions, these experiments failed to reveal evidence that Lotus has responded evolutionarily to the double invasion of Medicago followed by H. brunneipennis. However, when herbivory from H. brunneipennis was experimentally reduced, Lotus plants from source populations invaded by Medicago outperformed plants from uninvaded source populations when transplanted into heavily invaded destination environments. Therefore, Lotus showed evidence of adaptation to Medicago invasion but not to the newer invasion of an exotic shared herbivore. The presence of this exotic insect herbivore alters the outcome of evolutionary responses in this system and counteracts adaptation by the native Lotus to invasion by the exotic plant Medicago. This result has broad implications for the conservation of native communities. While native species may be able to adapt to the presence of one or a few exotics, a multitude of invasions may limit the ability of natives to respond evolutionarily to the novel and frequently changing selection pressures that arise with subsequent invasions.     

Asynchronous range shifts drive alpine plant–pollinator interactions and reduce plant fitness

Climate change is driving species' range shifts, which are in turn disrupting species interactions due to species‐specific differences in their abilities to migrate in response to climate. We evaluated the consequences of asynchronous range shifts in an alpine plant–pollinator community by transplanting replicated alpine meadow turfs downslope along an elevational gradient thereby introducing them to warmer climates and novel plant and pollinator communities. We asked how these novel plant–pollinator interactions affect plant reproduction. We found that pollinator communities differed substantially across the elevation/temperature gradient, suggesting that these plants will likely interact with different pollinator communities with warming climate. Contrary to the expectation that floral visitation would increase monotonically with warmer temperatures at lower elevations, visitation rate to the transplanted communities peaked under intermediate warming at midelevation sites. In contrast, visitation rate generally increased with temperature for the local, lower elevation plant communities surrounding the experimental alpine turfs. For two of three focal plant species in the transplanted high‐elevation community, reproduction declined at warmer sites. For these species, reproduction appears to be dependent on pollinator identity such that reduced reproduction may be attributable to decreased visitation from key pollinator species, such as bumble bees, at warmer sites. Reproduction in the third focal species appears to be primarily driven by overall pollinator visitation rate, regardless of pollinator identity. Taken together, the results suggest climate warming can indirectly affect plant reproduction via changes in plant–pollinator interactions. More broadly, the experiment provides a case study for predicting the outcome of novel species interactions formed under changing climates.     

Convergent structure of multitrophic communities over three continents

Ecological theory predicts that communities using the same resources should have similar structure, but evolutionary constraints on colonisation and niche shifts may hamper such convergence. Multitrophic communities of wasps exploiting fig fruits, which first evolved about 75MYA, do not show long‐term ‘inheritance’ of taxonomic (lineage) composition or species diversity. However, communities on three continents have converged ecologically in the presence and relative abundance of five insect guilds that we define. Some taxa fill the same niches in each community (phylogenetic niche conservatism). However, we show that overall convergence in ecological community structure depends also on a combination of niche shifts by resident lineages and local colonisations of figs by other insect lineages. Our study explores new ground, and develops new heuristic tools, in combining ecology and phylogeny to address patterns in the complex multitrophic communities of insect on plants, which comprise a large part of terrestrial biodiversity.     

An alien in an archipelago: Spathodea campanulata and the geographic variability of its moth (Lepidoptera) communities in the New Guinea and Bismarck Islands

Aim This analysis of moth (Lepidoptera) communities colonizing an alien tree invading secondary rain forest vegetation in Melanesia examines the predictability of insect herbivorous communities across distances of tens to thousands of km and the effect of dispersal barriers on community composition in the tropics. Location Six secondary rain forest sites were studied within four equidistant yet distinct geographic areas of the New Guinea mainland and the Bismarck Archipelago, including two watershed areas (Madang and Sepik) on mainland New Guinea and the adjacent large island of New Britain and small island of Unea. Methods The analysis is based on feeding records obtained by quantitative sampling and rearing of caterpillars from the alien host Spathodea campanulata (Bignoniaceae). It examines the variation in Lepidoptera community composition at six study sites distributed on three adjacent islands ranging in size from 30 to 865,000 km². Results Spathodea campanulata was colonized by 54 folivorous species of Lepidoptera. Most of them were generalists, feeding on > 1 native plant family. However, the three most abundant species representing 83% of all individuals (Acherontia lachesis, Hyblaea puera complex and Psilogramma menephron) were relatively host specific, feeding predominantly on a single native family that is not the Bignoniaceae. Most of the 23 species analysed in detail had a wide geographic distribution, including 13 species spanning the entire 1000‐km study transect. While the Lepidoptera in two New Guinea areas 280 km apart were similar to each other, there was a discontinuity in species composition between New Guinea and the smaller islands. However, no negative effect of small islands on species richness was detected. Main conclusions Spathodea campanulata was rapidly colonized by folivorous Lepidoptera communities with species richness and dominance structure indistinguishable from the assemblages feeding on native hosts, despite its phylogenetic isolation from the native vegetation. Although most species were generalists, the highest population densities were reached by relatively specialized species, similar to the communities on native hosts. The species turnover across distances from 10 to 1000 km was relatively low as most of the species had wide geographic ranges.     

Native plant diversity increases herbivory to non-natives

There is often an inverse relationship between the diversity of a plant community and the invasibility of that community by non-native plants. Native herbivores that colonize novel plants may contribute to diversity–invasibility relationships by limiting the relative success of non-native plants. Here, we show that, in large collections of non-native oak trees at sites across the USA, non-native oaks introduced to regions with greater oak species richness accumulated greater leaf damage than in regions with low oak richness. Underlying this trend was the ability of herbivores to exploit non-native plants that were close relatives to their native host. In diverse oak communities, non-native trees were on average more closely related to native trees and received greater leaf damage than those in depauperate oak communities. Because insect herbivores colonize non-native plants that are similar to their native hosts, in communities with greater native plant diversity, non-natives experience greater herbivory.     

Plant cover associated with aboveground net primary productivity (ANPP) mediates insect community composition in steppes of Northwest China

Temperate steppe is one of the most important natural habitats for the conservation of arthropod and bird biodiversity across the Eurasian Tectonic Plate. Since 1950, fragmentation of the steppe habitat has caused a loss of biodiversity and degradation of the species communities found in natural steppe. Therefore, in this study, both plants and insects were sampled at 56 sites in the steppe biome of northwestern China to explore the effects of plant community on insect community composition and diversity. The insect community structure varied in the four different steppe types (meadow steppe, typical steppe, desert steppe, and steppe desert). Plant cover (diversity) was an important driving force, which could enhance number of families and abundance of an insect community. Aboveground net primary productivity and water content of plants had no significant effects on insect community, although the plant community as a whole did mediate insect composition and community structure. Future research should explore the ecological role of particular functional groups in plant and insect communities. Supplemental sowing to improve plant diversity in steppe habitat may be another strategy to enhance biodiversity and achieve sustainable management.     

Site‐specific responses of native and exotic species to disturbances in a mesic grassland community

Abstract. Grassland communities are increasingly recognized as disturbance‐dependent ecosystems, yet there are few replicated, multi‐site studies documenting vegetation responses to varying frequencies and types of grassland disturbance. Even so, land managers frequently manipulate disturbance regimes in an attempt to favour native grassland plants over exotic species. We conducted a factorial experiment testing three frequencies of clipping combined with litter accumulation, litter removal, and soil disturbance within the highly threatened California coastal prairie plant community. We monitored the response of native/exotic, grass/forb plant guilds once a year for four years. More frequent clipping reduced cover of exotic grasses and favoured exotic forbs, whereas native species were largely unaffected by clipping frequency. Litter accumulation, litter removal, and soil disturbance did not affect vegetation composition. Effects of litter accumulation may take longer than our experiment allowed, and soil disturbance due to our treatments was not sufficiently strong to show consistent effects relative to mammalian soil disturbance. Treatment response of some plant guilds differed among sites, highlighting the importance of replicating experiments at several sites before recommending conservation management practices.     

Invertebrate herbivory along a gradient of plant species diversity in extensively managed grasslands

Increasing plant diversity has long been hypothesized to negatively affect levels of invertebrate herbivory due to a lower number of specialist insect herbivores in more diverse sites, but studies of natural systems have been rare. We used a planned comparison to study herbivory in a set of 19 semi-natural montane grasslands managed as hay meadows. Herbivory was measured in transects through the plant communities, and in individuals of Plantago lanceolata and Trifolium pratense that were transplanted into each meadow. In addition, plant community biomass and arthropod abundances were determined in the grasslands. Before the first mowing in June, mean herbivory levels correlated negatively with plant species richness, as predicted by theory, but they were also significantly affected by plant community biomass and plant community composition. After mowing, herbivory levels were only significantly related to plant community composition. Damage levels in the transplants were lower than herbivory levels in the established plant communities. Most insect herbivores were generalists and not specialists. The number of insect herbivores and spiders were positively correlated and tended to increase with increasing plant species richness. Herbivory levels were correlated negatively with spider abundances. We conclude that while the predicted negative relationship between plant species richness and insect herbivory can be found in grasslands, the underlying mechanism involves generalist rather than specialist herbivores. Our data also suggest a role of natural enemies in generalist herbivore activities.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .