Multitrophic Interactions Research Articles

Botryosphaeriaceae Species Associated with Stem Canker, Shoot Blight and Dieback of Fraxinus ornus in Italy

A severe dieback of flowering ash (Fraxinus ornus L.) has been observed in north-central Italy in the last decades. Symptoms include typical sunken, light-brown cankers on the stem and branches; vascular discoloration; tip and shoot dieback; and foliage necroses. The disease was more evident at the beginning of the growing season, and more severe on young regeneration. Six Botryosphaeriaceae species were consistently isolated from symptomatic plant tissues: Botryosphaeria dothidea, Diplodia fraxini, Diplodia subglobosa, Dothiorella iberica, Dothiorella omnivora and Neofusicoccum parvum. B. dothidea and D. fraxini expressed higher aggressiveness and showed a widespread incidence, being the species most frequently associated with cankers; the other four species were less virulent and more erratic, occurring mainly on succulent branch tips and foliage. Isolates were characterized using morphological and molecular approaches (colony/conidial phenotyping and rDNA-ITS genotyping). Phylogenetic analysis provided congruent phylogenies depicting the relationships of the six taxa with the most closely related conspecifics. Pathogenicity tests on 2-year-old seedlings confirmed the higher virulence of B. dothidea and D. fraxini. Extensive, multi-year field surveys at different sites supported the hypothesis that climatic vagaries, mainly heat, water and drought stresses, impaired tree health and vigor, facilitating infection and pervasive colonization by these Botryosphaeriaceae species. Environmental stressors are thus the key factor bringing the six fungal pathogens together in a multitrophic interaction with F. ornus in a novel, lethal fashion.

Soil organic carbon loss decreases biodiversity but stimulates multitrophic interactions that promote belowground metabolism.

Soil organic carbon (SOC) plays an essential role in mediating community structure and metabolic activities of belowground biota. Unraveling the evolution of belowground communities and their feedback mechanisms on SOC dynamics helps embed the ecology of soil microbiome into carbon cycling, which serves to improve biodiversity conservation and carbon management strategy under global change. Here, croplands with a SOC gradient were used to understand how belowground metabolisms and SOC decomposition were linked to the diversity, composition, and co-occurrence networks of belowground communities encompassing archaea, bacteria, fungi, protists, and invertebrates. As SOC decreased, the diversity of prokaryotes and eukaryotes also decreased, but their network complexity showed contrasting patterns: prokaryotes increased due to intensified niche overlap, while that of eukaryotes decreased possibly because of greater dispersal limitation owing to the breakdown of macroaggregates. Despite the decrease in biodiversity and SOC stocks, the belowground metabolic capacity was enhanced as indicated by increased enzyme activity and decreased enzymatic stoichiometric imbalance. This could, in turn, expedite carbon loss through respiration, particularly in the slow-cycling pool. The enhanced belowground metabolic capacity was dominantly driven by greater multitrophic network complexity and particularly negative (competitive and predator-prey) associations, which fostered the stability of the belowground metacommunity. Interestingly, soil abiotic conditions including pH, aeration, and nutrient stocks, exhibited a less significant role. Overall, this study reveals a greater need for soil C resources across multitrophic levels to maintain metabolic functionality as declining SOC results in biodiversity loss. Our researchers highlight the importance of integrating belowground biological processes into models of SOC turnover, to improve agroecosystem functioning and carbon management in face of intensifying anthropogenic land-use and climate change.

Interaction with the entomopathogenic fungus Beauveria bassiana influences tomato phenome and promotes resistance to Botrytis cinerea infection.

Plants are central to complex networks of multitrophic interactions. Increasing evidence suggests that beneficial microorganisms (BMs) may be used as plant biostimulants and pest biocontrol agents. We investigated whether tomato (Solanum lycopersicum) plants are thoroughly colonized by the endophytic and entomopathogenic fungus Beauveria bassiana, and how such colonization affects physiological parameters and the phenotype of plants grown under unstressed conditions or exposed to the pathogenic fungus Botrytis cinerea. As a positive control, a strain of the well-known biocontrol agent and growth inducer Trichoderma afroharzianum was used. As multitrophic interactions are often driven by (or have consequences on) volatile organic compounds (VOCs) released by plants constitutively or after induction by abiotic or biotic stresses, VOC emissions were also studied. Both B. bassiana and T. afroharzianum induced a significant but transient (one to two-day-long) reduction of stomatal conductance, which may indicate rapid activation of defensive (rejection) responses, but also limited photosynthesis. At later stages, our results demonstrated a successful and complete plant colonization by B. bassiana, which induced higher photosynthesis and lower respiration rates, improved growth of roots, stems, leaves, earlier flowering, higher number of fruits and yield in tomato plants. Beauveria bassiana also helped tomato plants fight B. cinerea, whose symptoms in leaves were almost entirely relieved with respect to control plants. Less VOCs were emitted when plants were colonized by B. bassiana or infected by B. cinerea, alone or in combination, suggesting no activation of VOC-dependent defensive mechanisms in response to both fungi.

Agricultural soil legacy influences multitrophic interactions between crops, their pathogens and pollinators.

Soil legacy influences plant interactions with antagonists and below-ground mutualists. Plant-antagonist interactions can jeopardize plant-pollinator interactions, while soil mutualists can enhance plant-pollinator interactions. This suggests that soil legacy, either directly or mediated through plant symbionts, affects pollinators. Despite the importance of pollinators to natural and managed ecosystems, information on how soil legacy affects plant-pollinator interactions is limited. We assessed effects of soil management legacy (organic versus conventional) on floral rewards and plant interactions with wild pollinators, herbivores, beneficial fungi and pathogens. We used an observational dataset and structural equation models to evaluate hypothesized relationships between soil and pollinators, then tested observed correlations in a manipulative experiment. Organic legacy increased mycorrhizal fungal colonization and improved resistance to powdery mildew, which promoted pollinator visitation. Further, soil legacy and powdery mildew independently and interactively impacted floral traits and floral reward nutrients, which are important to pollinators. Our results indicate that pollination could be an overlooked consequence of soil legacy and suggests opportunity to develop long-term soil management plans that benefit pollinators and pollination.

Invasive earthworms modulate native plant trait expression and competition

Biological invasions have major impacts on a variety of ecosystems and threaten native biodiversity. Earthworms have been absent from northern parts of North America since the last ice age, but non‐native earthworms were recently introduced there and are now being spread by human activities. While past work has shown that plant communities in earthworm‐invaded areas change towards a lower diversity mainly dominated by grasses, the underlying mechanisms related to changes in the biotic interactions of the plants are not well understood. Here, we used a trait‐based approach to study the effect of earthworms on interspecific plant competition and aboveground herbivory. We conducted a microcosm experiment in a growth chamber with a full‐factorial design using three plant species native to northern North American deciduous forests, Poa palustris (grass), Symphyotrichum laeve (herb) and Vicia americana (legume), either growing in monoculture or in a mixture of three. These plant community treatments were crossed with earthworm (presence or absence) and herbivore (presence or absence) treatments. Eight out of the fourteen above‐ and belowground plant functional traits studied were significantly affected by earthworms, either by a general effect or in interaction with plant species identity, plant diversity level and/or herbivore presence. Earthworms increased the aboveground productivity and the number of inflorescences of the grass P. palustris. Further, earthworms and herbivores together affected root tissue density of P. palustris and the specific leaf area of V. americana. In this study, earthworm presence gave a competitive advantage to the grass species P. palustris by inducing changes in plant functional traits. Our results suggest that invasive earthworms can alter competitive and multitrophic interactions of plants, shedding light on some of the mechanisms behind invasive earthworm‐induced plant community changes in northern North America forests.

Hypoxia and salinity constrain the sediment microbiota-mediated N removal potential in an estuary: A multi-trophic interrelationship perspective

Reactive nitrogen (N) enrichment is a common environmental problem in estuarine ecosystems, while the microbial-mediated N removal process is complicated for other multi-environmental factors. Therefore, A systematic investigation is necessary to understand the multi-trophic microbiota-mediated N removal characteristics under various environmental factors in estuaries. Here, we studied how multiple factors affect the multi-trophic microbiota-mediated N removal potential (denitrification and anammox) and N2O emission along a river-estuary-bay continuum in southeastern China using the environmental DNA (eDNA) approach. Results suggested that hypoxia and salinity were the dominant environmental factors affecting multi-trophic microbiota-mediated N removal in the estuary. The synergistic effect of hypoxia and salinity contributed to the loss of taxonomic (MultiTaxa) and phylogenetic (MultiPhyl) diversity across multi-trophic microbiota and enhanced the interdependence among multi-trophic microbiota in the estuary. The N removal potential calculated as the activities of key N removal enzymes was also significantly constrained in the estuary (0.011), compared with the river (0.257) and bay (0.461). Structural equation modeling illustrated that metazoans were central to all sediment N removal potential regulatory pathways. The top-down forces (predation by metazoans) restrained the growth of heterotrophic bacteria, which may affect microbial N removal processes in the sediment. Furthermore, we found that the hypoxia and salinity exacerbated the N2O emission in the estuary. This study clarifies that hypoxia and salinity constrain estuarine multi-trophic microbiota-mediated N removal potential and highlights the important role of multi-trophic interactions in estuarine N removal, providing a new perspective on mitigating estuarine N accumulation.

Linking Anthropogenic Landscape Perturbation to Herbivory and Pathogen Leaf Damage in Tropical Tree Communities.

Anthropogenic disturbance of tropical humid forests leads to habitat loss, biodiversity decline, landscape fragmentation, altered nutrient cycling and carbon sequestration, soil erosion, pest/pathogen outbreaks, among others. Nevertheless, the impact of these alterations in multitrophic interactions, including host-pathogen and vector-pathogen dynamics, is still not well understood in wild plants. This study aimed to provide insights into the main drivers for the incidence of herbivory and plant pathogen damage, specifically, into how vegetation traits at the local and landscape scale modulate such interactions. For this purpose, in the tropical forest of Calakmul (Campeche, Mexico), we characterised the foliar damage caused by herbivores and pathogens in woody vegetation of 13 sampling sites representing a gradient of forest disturbance and fragmentation in an anthropogenic landscape from well preserved to highly disturbed and fragmented areas. We also evaluated how the incidence of such damage was modulated by the vegetation and landscape attributes. We found that the incidence of damage caused by larger, mobile, generalist herbivores, was more sensitive to changes in landscape configuration, while the incidence of damage caused by small and specialised herbivores with low dispersal capacity was more influenced by vegetation and landscape composition. In relation to pathogen symptoms, the herbivore-induced foliar damage seems to be the main factor related to their incidence, indicating the enormous importance of herbivorous insects in the modulation of disease dynamics across tropical vegetation, as they could be acting as vectors and/or facilitating the entry of pathogens by breaking the foliar tissue and the plant defensive barriers. The incidence of pathogen damage also responded to vegetation structure and landscape configuration; the incidence of anthracnose, black spot, and chlorosis, for example, were favoured in sites surrounded by smaller patches and a higher edge density, as well as those with a greater aggregation of semi-evergreen forest patches. Fungal pathogens were shown to be an important cause of foliar damage for many woody species. Our results indicate that an increasing transformation and fragmentation of the tropical forest of southern Mexico could reduce the degree of specialisation in plant-herbivore interactions and enhance the proliferation of generalist herbivores (chewers and scrapers) and of mobile leaf suckers, and consequently, the proliferation of some symptoms associated with fungal pathogens such as fungus black spots and anthracnose. The symptoms associated with viral and bacterial diseases and to nutrient deficiency, such as chlorosis, could also increase in the vegetation in fragmented landscapes with important consequences in the health and productivity of wild and cultivated plant species. This is a pioneering study evaluating the effect of disturbances on multitrophic interactions, offering key insights on the main drivers of the changes in herbivory interactions and incidence of plant pathogens in tropical forests.

An improved method for extraction of soil fungal mycelium

Fungal mycelium is a major component of the soil microbiome. The soil hyphosphere represents a complex and dynamic niche for specific microorganisms, where multitrophic interactions occur, affecting ecosystem processes. However, extracting fungal mycelium from the soil to enable its taxonomical, chemical, and structural characterisation is challenging in the absence of a fast, efficient, and low-cost procedure. In this study, an old method (Bingle and Paul 1985), based on successive soil wet filtrations and density gradient centrifugation, was improved and tested in three different soil types (silty clay, silty clay loam, and loamy sand). The improved method reduced the number of filtrations by about five times and the centrifugation time from 40 min to 1 min. It avoided using any chemical substance which may impair further chemical analyses or DNA isolation and amplification. The method efficiency was about 50 % in the clay and 23 % in the sandy soils. However, a pre-step consisting of removing the fine-root fragments and other debris under the stereomicroscope may increase the method efficiency to more than 65 %, independent of the soil type.•A simple, efficient, and low-cost method suitable for extracting soil mycelium from a large number of samples.•The protocol includes successive soil wet filtrations and sucrose gradient centrifugation.•The method efficiency increases if the fine-root fragments and other debris are previously removed from the soil.

Water stress decreases the biocontrol efficacy of a nucleopolyhedrovirus against the fall armyworm on maize

Drought events are expected to limit crop productivity in the context of current climate change. Drought is also likely to affect multitrophic interactions such as those involving plants, phytophagous insects and their natural enemies. We designed a two-phase experiment to test the effect of water availability and fertilizer treatment on the interaction between maize, the fall armyworm and its nucleopolyhedrovirus pathogen. Plants grown in soil with high irrigation and mineral fertilization had the highest shoot and root dry weight. Furthermore, plant nitrogen levels were higher in plants with fertilization and a low irrigation scheme compared to other treatments. Low irrigation of maize plants reduced virus-induced mortality of armyworm larvae. Insects did not feed on plants with high irrigation and without fertilization. We conclude that water stress and plant nutrition can affect virus performance and thereby affect the efficiency of biological control and pest management, especially as water and nutrient limitation will likely increase under climate change.

Habitat fragmentation increases specialization of multi-trophic interactions by high species turnover.

Habitat fragmentation is altering species interactions worldwide. However, the mechanisms underlying the response of network specialization to habitat fragmentation remain unknown, especially for multi-trophic interactions. We here collected a large dataset consisting of 2670 observations of tri-trophic interactions among plants, sap-sucking aphids and honeydew-collecting ants on 18 forested islands in the Thousand Island Lake, China. For each island, we constructed an antagonistic plant-aphid and a mutualistic aphid-ant network, and tested how network specialization varied with island area and isolation. We found that both networks exhibited higher specialization on smaller islands, while only aphid-ant networks had increased specialization on more isolated islands. Variations in network specialization among islands was primarily driven by species turnover, which was interlinked across trophic levels as fragmentation increased the specialization of both antagonistic and mutualistic networks through bottom-up effects via plant and aphid communities. These findings reveal that species on small and isolated islands display higher specialization mainly due to effects of fragmentation on species turnover, with behavioural changes causing interaction rewiring playing only a minor role. Our study highlights the significance of adopting a multi-trophic perspective when exploring patterns and processes in structuring ecological networks in fragmented landscapes.

Multitrophic interactions between coccinellids and their parasitoids in natural and managed plant systems: host plant and aphid prey species matter

Multitrophic interactions between coccinellids and their parasitoids in natural and managed plant systems: host plant and aphid prey species matter

Global change in above-belowground multitrophic grassland communities

Global change is transforming Earth’s ecological communities with severe consequences for the functions and services they provide. In temperate grasslands, home to a mesmerising diversity of invertebrates controlling multiple ecosystem processes and services, land-use intensification and climate change are two of the most important global-change drivers. While we know a lot about their independent effects on grassland biodiversity and ecosystem functioning, little is known about how these stressors interact. Moreover, most research on biodiversity change focuses on decreasing biomass or species richness, while a major aspect is commonly ignored – altered ecological interactions. This is problematic because these interactions represent and control many important ecosystem processes, such as predation, herbivory or decomposition. Networks of trophic interactions, so-called food webs, link the structure and functioning of ecological communities and unravel mechanistic relationships between environmental change, ecological communities and ecosystem multifunctionality – the ability of a system to simultaneously support multiple processes. Consequently, we need to study how ecological interactions and the food webs they comprise respond to environmental change and to multiple interacting global-change drivers. Fortunately, novel tools offer unprecedented opportunities in studying trophic interactions and their impact on ecosystem processes. In addition, we know far more about how global change impacts the aboveground world than its belowground counterpart. However, belowground communities are just as important for the overall functioning of terrestrial ecosystems. Thus, to comprehensively understand global-change impacts on temperate grasslands, we need to study above- and belowground multitrophic interactions and ecosystem processes together, also accounting for their interdependencies. Here, we propose to use the Global Change Experimental Facility (GCEF, Bad Lauchstädt, Germany) to study joint impacts of land-use intensity and climate change on above-belowground multitrophic interactions and ecosystem multifunctionality in a temperate grassland global-change experiment. We will combine novel approaches to assessing trophic interactions and basal-resource dependency with an innovative method to quantify energy flux through ecological interaction networks. We will disentangle separate and interactive effects of land use and climate change and unravel how global-change driven modifications in multitrophic interactions mechanistically translate into altered ecosystem processes and multifunctionality – above and below the ground. Combining a field-experimental approach with novel molecular and quantitative techniques will allow for a leap forward in our understanding of global-change impacts on temperate grasslands, which will be crucial to manage and conserve these important ecosystems.

Supervised machine learning improves general applicability of eDNA metabarcoding for reservoir health monitoring

Effective and standardized monitoring methodologies are vital for successful reservoir restoration and management. Environmental DNA (eDNA) metabarcoding sequencing offers a promising alternative for biomonitoring and can overcome many limitations of traditional morphological bioassessment. Recent attempts have even shown that supervised machine learning (SML) can directly infer biotic indices (BI) from eDNA metabarcoding data, bypassing the cumbersome calculation process of BI regardless of the taxonomic assignment of eDNA sequences. However, questions surrounding the general applicability of this taxonomy-free approach to monitoring reservoir health remain unclear, including model stability, feature selection, algorithm choice, and multi-season biomonitoring. Here, we firstly developed a novel biological integrity index (Me-IBI) that integrates multitrophic interactions and environmental information, based on taxonomy-assigned eDNA metabarcoding data. The Me-IBI can better distinguish the actual health status of the Three Gorges Reservoir (TGR) than physicochemical assessments and have a clear response to human activity. Then, taking this reliable Me-IBI as a supervised label, we compared the impact of selecting different numbers of features and SML algorithms on the stability and predictive performance of the model for predicting ecological conditions in multiple seasons using taxonomy-free eDNA metabarcoding data. We discovered that even with a small number of features, different SML algorithms can establish a stable model and obtain excellent predictive performance. Finally, we proposed a four-step strategy for standardized routine biomonitoring using SML tools. Our study firstly explores the general applicability problem of the taxonomy-free eDNA-SML approach and establishes a solid foundation for the large-scale and standardized biomonitoring application.

Changes in longevity, parasitization rate and development time of the whitefly parasitoid Encarsia formosa under future climate conditions

Biological control by augmentative release of parasitoids is an established practice for controlling an economically very important insect pest group, whiteflies (Aleyrodidae), in protected cropping systems worldwide. One of the two most used parasitoids is Encarsia formosa. Anthropogenic climate change will modify multitrophic interactions between organisms, and sensitive biocontrol systems are not an exception. At the same time, there is a knowledge gap in our understanding of the performance of E. formosa as a biocontrol agent in mid-future climate. In the present study, we evaluate the parasitization rate, development time, and longevity of this important biocontrol agent by performing climatic chamber simulation driven by physically consistent, regionally downscaled, numerical future climate projections. The parasitoid shows 8.6 days accelerated development, 15-fold higher parasitization rate, and 38% shorter longevity under the tested future climate conditions. Challenges in conclusively assessing life parameters of this parasitoid, and the implications on whitefly biocontrol in the future are discussed.

Endophytic Beauveria bassiana of Tomato Resisted the Damage from Whitefly Bemisia tabaci by Mediating the Accumulation of Plant-Specialized Metabolites.

Beauveria bassiana acts as an endophytic fungus that controls herbivorous pests by stimulating plant defenses and inducing systemic resistance. Through multiomics analysis, 325 differential metabolites and 1739 differential expressed genes were observed in tomatoes treated with B. bassiana by root irrigation; meanwhile, 152 differential metabolites and 1002 differential genes were observed in tomatoes treated by local leaf spraying. Among the upregulated metabolites were α-solanine, 5-O-caffeoylshikimic acid, clerodendrin A, and peucedanin, which demonstrated anti-insect activity. These differential metabolites were primarily associated with alkaloid biosynthesis, flavonoid biosynthesis, and tryptophan metabolism pathways. Furthermore, the gene silencing of UDP-glucose:sterol glucosyltransferase, a gene involved in α-solanine synthesis, indicated that B. bassiana could inhibit the reproduction of whiteflies by regulating α-solanine. This study highlighted the ability of B. bassiana to modulate plant secondary metabolites and emphasized the significance of understanding and harnessing multitrophic interactions of endophytic B. bassiana for sustainable agriculture.

Aphid biological control in arable crops via flower strips: The predominant role of food resources over diversity effects

Abstract Plant taxonomic and functional diversity promotes interactions at higher trophic levels, but the contribution of functional diversity effects to multitrophic interactions and ecosystem functioning remains unclear. In agroecosystems, flower strips can be sown to promote biodiversity and associated services, but their plant composition is poorly considered from a functional diversity perspective so as to promote multitrophic interactions. In a field experiment, aphid biological control was compared across contrasting flower strip mixtures, over a 4‐year arable crop rotation. The effects of plants providing food resources, that is nectar and legumes supporting alternative hosts and prey, and the effects of plant species richness and functional dispersion were investigated on the biological control of aphid populations. In general, increases in the percentage of plant cover providing nectar and alternative prey (Fabaceae) to natural enemies increased predator–prey ratios and aphid parasitism and decreased aphid population growth rates. These effects however depended on the crop species. Species richness and the functional dispersion of traits involved in plant–arthropod interactions were of lesser importance, and the directions of their effects were crop‐specific. Synthesis and applications. These findings provide useful insight for designing perennial plant mixtures for creating or restoring habitats supporting aphid regulation. It is not adequate to sow any mixture containing simply flowering plants. Plant mixtures should comprise a large proportion of plant species supporting alternative prey, like legumes, and species producing nectar being easily accessible to natural enemies (corollas with nondeep nectar). To be efficient over a crop rotation, with aphids being present at different seasons, these nectar resources should be provided throughout the year thanks to a diversity of plant flowering periods.

Influence of biochar-triggered bottom-up effects on soil enzymes, soybean defenses, and the fitness of Spodoptera litura and its parasitoid

Bottom-up effects are major ecological forces in plant–herbivore–parasitoid multitrophic interactions. Biochar amendment in the field alters the bottom-up effects, as it can directly affect the soil environment and plant nutrient uptake, which in turn, indirectly affects herbivores and their natural enemies. However, such effects are poorly documented. We examined the influence of biochar on soil enzyme activity, soybean defense chemicals, and fitness of Spodoptera litura and its parasitoid Meteorus pulchricornis. As the biochar application rate increased, soil urease and sucrase activities, soybean trypsin protease inhibitor content, and polyphenol oxidase activity gradually increased. However, S. litura survival rate and adult body weight showed an initial increase, followed by a decrease, and then remained steady. Soil phosphatase activity initially increased and then stabilized, while M. pulchricornis cocoon emergence rate and fecundity showed an initial increase, followed by a decrease. Spodoptera litura adults preferred to oviposit on soybean at the 10 g/kg biochar level, whereas the parasitoids preferred the hosts at the 20 g/kg biochar level. Our results indicate that the biochar amendment of soils increased soil enzymes activity and soybean defenses, which had a positive effect on S. litura and M. pulchricornis at low levels, but became detrimental at high levels. The bottom-up effects triggered by biochar seemingly affected the second and third trophic levels, resulting in increased defense potential against herbivorous insects. Thus, biochar showed potential to enhance direct plant defenses against pests and indirectly influenced defenses mediated by natural enemies.

Conservation agriculture affects multitrophic interactions driving the efficacy of weed biological control

Abstract Biological control is a key ecosystem service in arable lands, but its effectiveness varies according to environmental and biotic contexts. Cascading interactions between several trophic levels can affect natural enemies and their efficacy. Here, we analysed how multitrophic interactions drive weed seed control under contrasting farming systems and landscapes. In particular, we analyse how the presence of higher‐order predators and alternative prey affects the weed seed consumption by seed predators. We monitored 30 cereal fields organised into 15 pairs, each comprising one conventional and one conservation agriculture field, sampled along a gradient of proportion of conservation agriculture in the landscape. We found that local and landscape management under conservation agriculture favours the presence of seed predators like carabids and rodents, higher‐order predators like shrews and alternative animal prey. Weed seed predation is promoted by conservation agriculture through an increase in the number of seed predators. However, alternative animal prey reduces the efficacy of carabids to consume seeds, probably due to a prey‐switching behaviour. Similarly, shrews negatively affect the activity‐density of carabids, resulting in an indirect negative effect on seed predation. Synthesis and applications: Our study highlights that the implementation of conservation agriculture can improve the provision of biological control but the resulting effect may be partially limited by the increased complexity of trophic interactions. The different trophic levels respond to local management and/or the surrounding landscape with cascading effects on the delivery of weed control. Our study highlights the importance of considering not only the direct effects of seed predators, but also the indirect effects of higher‐order predators and alternative prey when predicting the level of weed biological control.

Alterations in bee-plant-soil multitrophic interactions after fungicide soil application

Soil microorganisms play a key role in plant growth and health, and honey bees depend on plant pollen and nectar for their nutrition. Despite this clear above- and belowground connection, our knowledge about bee-plant-soil interactions is yet limited. Also, how these multitrophic interactions are affected by agricultural practices like pesticide applications is not well understood. Here we investigated possible non-target effects of soil application of the fungicide Benomyl on bee-plant-soil interactions in a greenhouse experiment with vetch (Vicia sativa L.). When plants were flowering honey bees were confined to their respective experimental soil treatments (untreated control, Benomyl and soil disinfection) in tents made from anti-insect mesh and micro-hives for foraging. At harvest, results showed that Benomyl and soil disinfection strongly affected key root and soil microorganisms essential for plant nutrition, such as mycorrhiza and rhizobia, and Gram-positive and Gram-negative bacteria, which coincided with phenotypic alterations in plant development and subsequently significant effects on honey bee nutrition and health, and finally honey production. In conclusion, our results show that soil application of the fungicide Benomyl strongly impact on bee-plant-soil multitrophic interactions, calling for further investigation on non-target effect of pesticides including multitrophic studies when evaluating environmental impacts of pesticides.

DNA barcoding resolves quantitative multi‐trophic interaction networks and reveals pest species in trap nests

Abstract Insects, as one of the most species‐rich taxa with enormous taxonomic, behavioural and functional diversity, are in decline. Bees and wasps are especially crucial for ecosystems as pollinators or to control populations of other insects. To understand population drivers, comprehensive knowledge about top‐down and bottom‐up interactions, including all interaction partners, is needed. Nests of trap‐nesting bees and wasps include multi‐trophic interactions between bees, wasps, their food resources and natural enemies, simultaneously, however, up to today, all trophic interactions are not yet included in trap nest research because of challenges to identify the food used by nesting bees and wasps. Here, we reconstructed quantitative three‐ and four‐trophic interaction networks of species in three apoid wasp families using DNA barcoding. The obtained tripartite and quadripartite networks encompassed natural enemy‐wasp‐spider and natural enemy‐wasp‐herbivore‐plant interactions. Moreover, we identified so far undescribed Hymenoptera‐prey interactions, including prey species known as agricultural and forest pests. More extensive research on bee and wasp multitrophic interaction networks will provide valuable insights to better understand responses to environmental and biodiversity change, to investigate ecological theory and to reveal so far unknown feeding links.