Distance functions of carabids in crop fields depend on functional traits, crop type and adjacent habitat: a synthesis.

Natural pest and weed regulation are essential for agricultural production, but the spatial distribution of natural enemies within crop fields and its drivers are mostly unknown. Using 28 datasets comprising 1204 study sites across eight Western and Central European countries, we performed a quantitative synthesis of carabid richness, activity densities and functional traits in relation to field edges (i.e. distance functions). We show that distance functions of carabids strongly depend on carabid functional traits, crop type and, to a lesser extent, adjacent non-crop habitats. Richness of both carnivores and granivores, and activity densities of small and granivorous species decreased towards field interiors, whereas the densities of large species increased. We found strong distance decays in maize and vegetables whereas richness and densities remained more stable in cereals, oilseed crops and legumes. We conclude that carabid assemblages in agricultural landscapes are driven by the complex interplay of crop types, adjacent non-crop habitats and further landscape parameters with great potential for targeted agroecological management. In particular, our synthesis indicates that a higher edge-interior ratio can counter the distance decay of carabid richness per field and thus likely benefits natural pest and weed regulation, hence contributing to agricultural sustainability.

Revegetation of vineyard terrace embankments: A matter of seed mixture and seeding technique.

Maintaining traditional agricultural management to preserve agrobiodiversity remains one of the major challenges for biodiversity conservation in Europe. In Germany, viticulture on steep slopes has shaped cultural landscapes of high conservational value but has declined strongly in recent decades due to insufficient profitability. One promising approach to keep management economically viable is modern vineyard terracing. Here, vineyard rows run parallel to the hillside, thus facilitating management and lowering production costs. At the same time, terrace embankments offer large non-cropped areas between the vines that could make a significant contribution to biodiversity. However, to fully exploit that potential sustainable revegetation of terrace embankments is mandatory but barely studied. For three consecutive years, we evaluated the effects of different seed mixtures (hay threshing, regional and commercial mixture), seeding techniques (manual vs. hydro-seeding), and the effect of nurse plants, hay mulch, and fertilizer on the establishment and maintenance of vegetation on three terraced vineyards in the Upper Middle Rhine Valley, Germany. The regional mixture best met the demands of biodiversity conservation by providing high herb and flower cover. Hay threshing and the regional mixture provided sufficient vegetation cover to reduce the risk of erosion, whereas the commercial mixture performed poorly in terms of vegetation cover and plant diversity. For hydro-seeding, target species richness was higher and bare ground cover was significantly reduced compared to manual seeding. Nurse plants, hay mulch, and fertilizer application only marginally improved plant establishment. Together these results emphasize that hydro-seeding with regional seeds is the best approach for revegetation of vineyard terrace embankments by combining high biodiversity and sufficient vegetation cover to reduce erosion risks at the best cost-benefit ratio for winegrowers. Vineyard terracing contributes to maintaining economically viable viticulture on steep slopes and may concurrently act as a conservation tool for biodiversity in vineyard landscapes.

Crop pests and predators exhibit inconsistent responses to surrounding landscape composition.

The idea that noncrop habitat enhances pest control and represents a win-win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win-win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies.

The effectiveness of flower strips and hedgerows on pest control, pollination services and crop yield: a quantitative synthesis.

Floral plantings are promoted to foster ecological intensification of agriculture through provisioning of ecosystem services. However, a comprehensive assessment of the effectiveness of different floral plantings, their characteristics and consequences for crop yield is lacking. Here we quantified the impacts of flower strips and hedgerows on pest control (18 studies) and pollination services (17 studies) in adjacent crops in North America, Europe and New Zealand. Flower strips, but not hedgerows, enhanced pest control services in adjacent fields by 16% on average. However, effects on crop pollination and yield were more variable. Our synthesis identifies several important drivers of variability in effectiveness of plantings: pollination services declined exponentially with distance from plantings, and perennial and older flower strips with higher flowering plant diversity enhanced pollination more effectively. These findings provide promising pathways to optimise floral plantings to more effectively contribute to ecosystem service delivery and ecological intensification of agriculture in the future.

Non-consumptive effects between predators depend on the foraging mode of intraguild prey.

Predator non-consumptive effects (NCE) are a suite of phenotypic responses of prey to avoid predation that cascade down food webs and can have a stronger impact than predation itself. However, the role of NCE in intraguild interactions remains understudied. Thus, multi-species experiments based on species traits are needed to improve our understanding of the impact of NCE on community structure. We investigated NCE of ants on 17 spider species as intraguild prey (8 cursorial and 9 sedentary) to test the influence of spider hunting mode on the strength of NCE. Sedentary spiders select a habitat patch and wait for prey, whereas cursorial spiders roam around searching for prey. Because actively foraging organisms have higher encounter rates with predators, cursorial spiders should show stronger reactions to ant presence. We collected cues (footprint hydrocarbons) of the black garden ant Lasius niger on filter papers. Then, we placed spiders individually on the papers and filmed their behaviour once on a paper with cues and once on a cue-free one. We used the increase in walking activity in the presence of cues as an indicator of avoidance behaviour towards ants. Cursorial spiders spent a longer time moving and being mobile, and had a higher overall mean mobility when exposed to ant cues compared with blank filter papers, whereas sedentary spider species did not react to ant cues at all. The avoidance of ant cues by cursorial spiders corresponds to their higher risk of encountering ants compared with sedentary species, in accordance with the threat-sensitivity hypothesis. Our multi-species study shows the relevance of NCE for intraguild interactions and highlights the importance of experimental trait-based approaches to improve predictability of species interactions and the role of NCE in ecological communities.

The interplay of landscape composition and configuration: new pathways to manage functional biodiversity and agroecosystem services across Europe.

Managing agricultural landscapes to support biodiversity and ecosystem services is a key aim of a sustainable agriculture. However, how the spatial arrangement of crop fields and other habitats in landscapes impacts arthropods and their functions is poorly known. Synthesising data from 49 studies (1515 landscapes) across Europe, we examined effects of landscape composition (% habitats) and configuration (edge density) on arthropods in fields and their margins, pest control, pollination and yields. Configuration effects interacted with the proportions of crop and non-crop habitats, and species' dietary, dispersal and overwintering traits led to contrasting responses to landscape variables. Overall, however, in landscapes with high edge density, 70% of pollinator and 44% of natural enemy species reached highest abundances and pollination and pest control improved 1.7- and 1.4-fold respectively. Arable-dominated landscapes with high edge densities achieved high yields. This suggests that enhancing edge density in European agroecosystems can promote functional biodiversity and yield-enhancing ecosystem services.

An updated perspective on spiders as generalist predators in biological control.

The role of generalist predators in biological control remains controversial as they may not only reduce pest populations but also disrupt biocontrol exerted by other natural enemies. Here, we focus on spiders as a model group of generalist predators. They are among the most abundant and most diverse natural enemies in agroecosystems. We review their functional traits that influence food-web dynamics and pest suppression at organisational levels ranging from individuals to communities. At the individual and population levels, we focus on hunting strategy, body size, life stage, nutritional target, and personality (i.e., consistent inter-individual differences in behaviour). These functional traits determine the spider trophic niches. We also focus on the functional and numerical response to pest densities and on non-consumptive effects of spiders on pests. At the community level, we review multiple-predator effects and effect of alternative prey on pest suppression. Evidence for a key role of spiders in pest suppression is accumulating. Importantly, recent research has highlighted widespread non-consumptive effects and complex intraguild interactions of spiders. A better understanding of these effects is needed to optimize biocontrol services by spiders in agroecosystems.

Non-bee insects are important contributors to global crop pollination.

Wild and managed bees are well documented as effective pollinators of global crops of economic importance. However, the contributions by pollinators other than bees have been little explored despite their potential to contribute to crop production and stability in the face of environmental change. Non-bee pollinators include flies, beetles, moths, butterflies, wasps, ants, birds, and bats, among others. Here we focus on non-bee insects and synthesize 39 field studies from five continents that directly measured the crop pollination services provided by non-bees, honey bees, and other bees to compare the relative contributions of these taxa. Non-bees performed 25-50% of the total number of flower visits. Although non-bees were less effective pollinators than bees per flower visit, they made more visits; thus these two factors compensated for each other, resulting in pollination services rendered by non-bees that were similar to those provided by bees. In the subset of studies that measured fruit set, fruit set increased with non-bee insect visits independently of bee visitation rates, indicating that non-bee insects provide a unique benefit that is not provided by bees. We also show that non-bee insects are not as reliant as bees on the presence of remnant natural or seminatural habitat in the surrounding landscape. These results strongly suggest that non-bee insect pollinators play a significant role in global crop production and respond differently than bees to landscape structure, probably making their crop pollination services more robust to changes in land use. Non-bee insects provide a valuable service and provide potential insurance against bee population declines.

Contrasting effects of aquatic subsidies on a terrestrial trophic cascade.

Subsidies from adjacent ecosystems can alter recipient food webs and ecosystem functions, such as herbivory. Emerging aquatic insects from streams can be an important prey in the riparian zone. Such aquatic subsidies can enhance predator abundances or cause predators to switch prey, depending on the herbivores. This can lead to an increase or decrease of in situ herbivores and herbivory. We examined the effects of aquatic subsidies on a simplified terrestrial food web consisting of two types of herbivores, plants and predators (spiders). In our six-week experiment, we focused on the prey choice of the spiders by excluding predator immigration and reproduction. In accordance with predator switching, survival of leafhoppers increased in the presence of aquatic subsidies. By contrast, the presence of aquatic subsidies indirectly reduced weevils and herbivory. Our study shows that effects of aquatic subsidies on terrestrial predators can propagate through the food web in contrasting ways. Thereby, the outcome of the trophic cascade is determined by the prey choice of predators.

Impacts of invasive plants on resident animals across ecosystems, taxa, and feeding types: a global assessment.

As drivers of global change, biological invasions have fundamental ecological consequences. However, it remains unclear how invasive plant effects on resident animals vary across ecosystems, animal classes, and functional groups. We performed a comprehensive meta-analysis covering 198 field and laboratory studies reporting a total of 3624 observations of invasive plant effects on animals. Invasive plants had reducing (56%) or neutral (44%) effects on animal abundance, diversity, fitness, and ecosystem function across different ecosystems, animal classes, and feeding types while we could not find any increasing effect. Most importantly, we found that invasive plants reduced overall animal abundance, diversity and fitness. However, this significant overall effect was contingent on ecosystems, taxa, and feeding types of animals. Decreasing effects of invasive plants were most evident in riparian ecosystems, possibly because frequent disturbance facilitates more intense plant invasions compared to other ecosystem types. In accordance with their immediate reliance on plants for food, invasive plant effects were strongest on herbivores. Regarding taxonomic groups, birds and insects were most strongly affected. In insects, this may be explained by their high frequency of herbivory, while birds demonstrate that invasive plant effects can also cascade up to secondary consumers. Since data on impacts of invasive plants are rather limited for many animal groups in most ecosystems, we argue for overcoming gaps in knowledge and for a more differentiated discussion on effects of invasive plant on native fauna.

High effectiveness of tailored flower strips in reducing pests and crop plant damage.

Providing key resources to animals may enhance both their biodiversity and the ecosystem services they provide. We examined the performance of annual flower strips targeted at the promotion of natural pest control in winter wheat. Flower strips were experimentally sown along 10 winter wheat fields across a gradient of landscape complexity (i.e. proportion non-crop area within 750 m around focal fields) and compared with 15 fields with wheat control strips. We found strong reductions in cereal leaf beetle(CLB) density (larvae: 40%; adults of the second generation: 53%) and plant damage caused by CLB (61%) in fields with flower strips compared with control fields. Natural enemies of CLB were strongly increased in flower strips and in part also in adjacent wheat fields. Flower strip effects on natural enemies, pests and crop damage were largely independent of landscape complexity(8-75% non-crop area). Our study demonstrates a high effectiveness of annual flower strips in promoting pest control, reducing CLB pest levels below the economic threshold. Hence, the studied flower strip offers a viable alternative to insecticides. This highlights the high potential of tailored agri-environment schemes to contribute to ecological intensification and may encourage more farmers to adopt such schemes.

Risk of spider predation alters food web structure and reduces local herbivory in the field.

Predators can indirectly enhance plant performance via herbivore suppression, with both prey consumption and changes in prey traits (e.g. changes in foraging behaviour) contributing to the reduction in herbivory. We performed a field experiment to determine the extent of such non-consumptive effects which consisted of repeatedly placing spiders (Pisaura mirabilis) on enclosed plants (Urtica dioica) for cue deposition. Control plants were enclosed in the same way but without spiders. After cue deposition, the enclosures were removed to allow arthropods to colonize the plants and feed on them. Arthropods were removed from the plants before the subsequent spider deposition or control enclosure. During six cycles of enclosure, we quantified leaf damage on the plants. After a seventh cycle, the colonizing arthropods were sampled to determine community composition in relation to the presence/absence of spider cues. We found that the presence of chemotactile spider cues reduced leaf damage by 50 %. In addition, spider cues led to changes in the arthropod community: smaller spiders avoided plants with spider cues. In contrast, the aphid-tending ant Myrmica rubra showed higher recruitment of workers on cue-bearing plants, possibly to protect aphids. Our results show that the risk of spider predation can reduce herbivory on wild plants and also demonstrate that non-consumptive effects can be particularly strong within the predator guild.

Disentangling multiple drivers of pollination in a landscape-scale experiment.

Animal pollination is essential for the reproductive success of many wild and crop plants. Loss and isolation of (semi-)natural habitats in agricultural landscapes can cause declines of plants and pollinators and endanger pollination services. We investigated the independent effects of these drivers on pollination of young cherry trees in a landscape-scale experiment. We included (i) isolation of study trees from other cherry trees (up to 350 m), (ii) the amount of cherry trees in the landscape, (iii) the isolation from other woody habitats (up to 200 m) and (iv) the amount of woody habitats providing nesting and floral resources for pollinators. At the local scale, we considered effects of (v) cherry flower density and (vi) heterospecific flower density. Pollinators visited flowers more often in landscapes with high amount of woody habitat and at sites with lower isolation from the next cherry tree. Fruit set was reduced by isolation from the next cherry tree and by a high local density of heterospecific flowers but did not directly depend on pollinator visitation. These results reveal the importance of considering the plant's need for conspecific pollen and its pollen competition with co-flowering species rather than focusing only on pollinators' habitat requirements and flower visitation. It proved to be important to disentangle habitat isolation from habitat loss, local from landscape-scale effects, and direct effects of pollen availability on fruit set from indirect effects via pollinator visitation to understand the delivery of an agriculturally important ecosystem service.

Sensitivity of spiders from different ecosystems to lambda-cyhalothrin: effects of phylogeny and climate.

BACKGROUND: In spite of their importance as arthropod predators, spiders have received little attention in the risk assessment of pesticides. In addition, research has mainly focused on a few species commonly found in agricultural habitats. Spiders living in more natural ecosystems may also be exposed to and affected by pesticides, including insecticides. However, their sensitivity and factors driving possible variations in sensitivity between spider taxa are largely unknown. To fill this gap, we quantified the sensitivity of 28 spider species from a wide range of European ecosystems to lambda-cyhalothrin in an acute exposure scenario. RESULTS: Sensitivity varied among the tested populations by a factor of 30. Strong differences in sensitivity were observed between families, but also between genera within the Lycosidae. Apart from the variation explained by the phylogeny, spiders from boreal and polar climates were more sensitive than spiders from warmer areas. Overall, the median lethal concentration (LC50 ) of 85% of species was below the recommended application rate of lambda-cyhalothrin (75 ng a.i. cm-2 ). CONCLUSION: Our study underlines the high sensitivity of spiders to lambda-cyhalothrin, which can lead to unintended negative effects on pest suppression in areas treated with this insecticide. The strong differences observed between families and genera indicate that the functional composition of spider communities would change in affected areas. Overall, the variation in spider sensitivity suggests that multispecies investigations should be more widely considered in pesticide risk assessment. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Variation in the Chemical Sensitivity of Earthworms from Field Populations to Imidacloprid and Copper.

The chemical risk of pesticides for nontarget soil macroorganisms has mainly been assessed using the compost earthworm Eisenia fetida. However, E. fetida does not occur in agroecosystems, and it is generally less sensitive than other earthworm species. Thus, the extrapolation of its response to pesticides to other earthworm species may lead to uncertainties in risk assessment. Because toxicity data for other earthworms are scarce, we assessed the chemical sensitivity of five species (Allolobophora chlorotica, Aporrectodea caliginosa, Aporrectodea longa, Aporrectodea rosea, and Lumbricus rubellus) from different habitats (forests, wetlands, and grasslands), as well as E. fetida, to imidacloprid and copper in single-species acute toxicity tests. In addition, we examined the relationship between earthworm traits (ecotype and weight), habitat characteristics (ecosystem type and soil pH), and chemical sensitivity. The lower limits of the hazardous concentration affecting 5% (HC5) of species were 178.99 and 0.32 mg active ingredient/kg dry weight for copper and imidacloprid, respectively. Some concentrations that have been measured in European agroecosystems for both pesticides were above the HC5s, indicating toxic risks for these organisms. Furthermore, soil pH from the sampling habitat played a significant role, with earthworms sampled from extremely acidic soils being less sensitive to copper than earthworms from neutral soils. In addition, endogeic earthworms were more sensitive to imidacloprid than epigeic earthworms. This may translate to changes in soil functions such as bioturbation, which is mainly carried out by endogeic earthworms. Our results suggest that risk assessment should include a wider range of earthworms covering different habitats and ecosystem functions to achieve a better protection of the biological functions carried out by these key soil organisms. Environ Toxicol Chem 2023;42:939-947. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Increase in breeding bird abundance and diversity with semi-natural habitat in vineyard landscapes.

Agricultural expansion and intensification are major threats to biodiversity, and even some once common farmland bird species are now endangered. Wine-growing landscapes are intensively managed but can still be an attractive habitat for a wide range of species. However, only few bird species breed within vineyards and thus, semi-natural habitat types like hedges, woodland patches and grasslands are crucial for bird populations. We investigated how birds breeding in wine-growing areas are influenced by the surrounding landscape at three spatial scales: territories, sampling transects and landscapes. In the German wine growing region Palatinate, sixteen landscapes with a radius of 500 m were chosen spanning a gradient in the cover of semi-natural habitat. Bird territories were mapped along three transects of 500 m length in each landscape. We found 300 territories of 33 bird species. Positive effects of semi-natural habitat cover on birds were strongest at the transect scale, with almost proportional increase of species and territory numbers with the cover of semi-natural habitat. Most bird species selected territories that contained more semi-natural habitat than the landscape-wide average of 13.5%, but e.g. woodlark and linnet showed an opposite preference. In addition, the birds' community composition was influenced by the composition of the surrounding landscape. Most species were associated with semi-natural habitat types or built-up areas while vineyards had hardly any species associated with them. Our results suggest that in wine-growing landscapes, the decline in farmland birds can be reversed by the re-establishment of hedges, trees, woodland patches, traditional orchards and grassland areas. However, as preferences at the territory scale were species-specific, there is no uniform best solution for bird conservation in viticultural landscapes. Thus, landscape development should always be accompanied by experts that take the demands of existing and potential breeding birds into account.

Aquatic-terrestrial transfer of neonicotinoid insecticides in riparian food webs.

Current-use pesticides are ubiquitous in freshwaters globally, often at very low concentrations. Emerging aquatic insects can accumulate pesticides during their aquatic development, which can be retained through their metamorphosis into terrestrial adults. Emerging insects thus provide a potential, yet largely understudied linkage for exposure of terrestrial insectivores to waterborne pesticides. We measured 82 low to moderately lipophilic organic pesticides (logKow: -2.87 to 6.9) in the aquatic environment, emerging insects and web-building riparian spiders from stream sites impacted by agricultural land use. Insecticides, mainly neuro-active neonicotinoids were ubiquitous and had the highest concentrations in emerging insects and spiders (∑ insecticides: 0.1-33 and 1-240 ng/g, respectively), although their concentrations in water were low, even when compared to global levels. Furthermore, neonicotinoids, although not considered to be bioaccumulative, were biomagnified in riparian spiders. In contrast, concentrations of fungicides and most herbicides decreased from the aquatic environment to the spiders. Our results provide evidence for the transfer and accumulation of neonicotinoids across the aquatic-terrestrial ecosystem boundary. This could threaten food webs in ecologically sensitive riparian areas worldwide.

Arthropods on grapes benefit more from fungicide reduction than from organic farming.

BACKGROUND: Pesticides are considered main contributors to global arthropod declines and therefore may decrease the provision of ecosystem services such as natural pest control. Organic farming and cultivating pest- and disease-resistant varieties can allow pesticide applications and their impacts on nontarget organisms and the environment to be reduced. We investigated the effects of organic versus conventional management and fungus-resistant versus susceptible wine grape varieties on arthropod biodiversity and pest control of grape berry moths in 32 vineyards in the Palatinate region, Germany. Hazard quotients of applied pesticides were calculated for each vineyard. RESULTS: The cultivation of fungus-resistant varieties led to significantly reduced hazard quotients and in turn enhanced abundances of natural enemies, particularly theridiid and philodromid spiders. Unexpectedly, organic management resulted in higher hazard quotients than conventional management and reduced numbers of natural enemies, particularly earwigs. Pest predation rates showed no significant differences between grape varieties or management types. CONCLUSION: Widespread benefits of organic management on arthropod biodiversity found in other crops were absent in our viticultural study region. This is likely due to the dominant role of fungal diseases in viticulture, which requires high numbers of fungicide treatments under both conventional and organic viticulture. Thus, fungicide reduction through the cultivation of fungus-resistant grape varieties is one key element to fostering the abundance of arthropods in general and beneficial arthropods in particular. Beyond vineyards, this is potentially relevant in numerous other crop types. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Impact across ecosystem boundaries - Does Bti application change quality and composition of the diet of riparian spiders?

Emerging aquatic insects link aquatic and adjacent terrestrial food webs by subsidizing terrestrial predators with high-quality prey. One of the main constituents of aquatic subsidy, the non-biting midges (Chironomidae), showed altered emergence dynamics in response to the mosquito control agent Bacillus thuringiensis var. israelensis (Bti). As riparian spiders depend on aquatic subsidy, they may be affected by such changes in prey availability. Thus, we conducted a field study in twelve floodplain pond mesocosms (FPMs), six were treated with Bti (2.88 × 109 ITU/ha, VectoBac WDG) three times, to investigate if the Bti-induced shift in chironomid emergence dynamics is reflected in their nutritional value and in the diet of riparian spiders. We measured the content of proteins, lipids, glycogen, and carbohydrates in emerged Chironomidae, and determined the stable isotope ratios of female Tetragnatha extensa, a web-building spider living in the riparian vegetation of the FPMs. We analysed the proportion of aquatic prey in spiders' diet, niche size, and trophic position. While the content of nutrients and thus the prey quality was not significantly altered by Bti, effects on the spiders' diet were observed. The trophic position of T. extensa from Bti-treated FPMs was lower compared to the control while the aquatic proportion was only minimally reduced. We assume that spiders fed more on terrestrial prey but also on other aquatic organisms such as Baetidae, whose emergence was unaffected by Bti. In contrast to the partly predaceous Chironomidae, consumption of aquatic and terrestrial primary consumers potentially explains the observed lower trophic position of spiders from Bti-treated FPMs. As prey organisms vary in their quality the suggested dietary shift could transfer previously observed effects of Bti to riparian spiders conceivably affecting their populations. Our results further support that anthropogenic stressors in aquatic ecosystems may translate to terrestrial predators through aquatic subsidy.

Benthic macroinvertebrate community shifts based on Bti-induced chironomid reduction also decrease Odonata emergence.

Chironomid larvae (Diptera: Chironomidae) often dominate aquatic macroinvertebrate communities and are a key food source for many aquatic predators, such as dragonfly and damselfly larvae (Odonata). Changes in aquatic macroinvertebrate communities may propagate through terrestrial food webs via altered insect emergence. Bacillus thuringiensis israelensis (Bti)-based larvicides are widely used in mosquito control but can also reduce the abundance of non-biting chironomid larvae. We applied the maximum field rate of Bti used in mosquito control three times to six mesocosms in a replicated floodplain pond mesocosm (FPM) system in spring for two consecutive years, while the remaining six FPMs were untreated. Three weeks after the third Bti application in the first year, we recorded on average a 41% reduction of chironomid larvae in Bti-treated FPMs compared to untreated FPMs and a shift in benthic macroinvertebrate community composition driven by the reduced number of chironomid, Libellulidae and Coenagrionidae larvae (Odonata). Additionally, the number of emerging Libellulidae (estimated by sampling of exuviae in the second year) was reduced by 54% in Bti-treated FPMs. Since Odonata larvae are not directly susceptible to Bti, our results suggest indirect effects due to reduced prey availability (i.e., chironomid larvae) or increased intraguild predation. As Libellulidae include species of conservation concern, the necessity of Bti applications to their habitats, e.g. floodplains, should be carefully evaluated.