Biology subjects

Steffan-Dewenter, I.

Publications and source records attributed to Steffan-Dewenter, I..

11 recordsLinked to original sources

bioRxiv2026

Nocturnal pollination services as an ecological safety net for papaya production in a tropical biodiversity hotspot

Pollination is of key importance for tropical agriculture, yet a bee-centred perspective often overlooks the critical role of nocturnal insects in pollination services. We evaluated the relative contributions of diurnal and nocturnal pollinators to papaya yields on subsistence farms in the Taita Hills, Kenya, a globally important biodiversity hotspot. We combined flower visitor observations with five experimental treatments: open pollination, wind-only (closed), hand pollination, and temporal exclusions for day-only and night-only services. Our results reveal complete temporal niche partitioning between diurnal bees and nocturnal hawkmoths (Sphingidae). We found that diurnal and nocturnal pollinators provide additive, rather than redundant, services, contributing to papaya fruit set and weight to a similar extent. Despite these contributions, supplementary hand-pollination experiments indicated a significant yield gap (36.9% lower fruit set), suggesting substantial pollinator limitation. While landscape-scale factors had no significant effects, nocturnal pollinators responded positively to organic management, whereas diurnal visitors did not. This indicates that local habitat quality and ecological intensification are more critical for sustaining specialised pollinators than landscape composition. Our study highlights the vital role of nocturnal insects as an ecological safety net and emphasises that their conservation through local organic practices is essential for securing yield quantity and quality in tropical papaya farming systems.

ecology↗

bioRxiv2026

Human landscape modification shapes foraging preferences and sucrose responsiveness of honey bees in Asia

Landscape composition is central in shaping how pollinators utilise floral resources, yet its influence on foraging behaviour of co-occurring Asian honey bees remains underexplored. Resolving this gap is crucial to understand how closely-related, native and introduced species maintain foraging efficiency in rapidly changing environments. We investigated nectar preferences, sucrose responsiveness, and foraging task partitioning in three co-occurring honey bee species in India: Apis florea (native open-nesting), Apis cerana (native cavity-nesting), and Apis mellifera (introduced cavity-nesting), across forest, agricultural, and urban landscapes. Landscape type strongly influenced crop sugar concentrations of honey bees. While all species collected high-concentration nectar in forests, A. mellifera and A. cerana collected lower concentrations than A. florea in urban habitats. A. florea showed consistent preference for high-concentration nectar across landscapes. Complementing this, sucrose responsiveness assays revealed a lower responsiveness of A. florea compared to cavity-nesting species. Foraging task partitioning differed among species, but interestingly, also among landscapes. While A. cerana predominantly collected nectar, A. mellifera foraged equally for pollen, nectar and water, and A. florea shifted task allocation across landscapes. In conclusion, we provide the first comparative evidence that landscape composition and species characteristics jointly shape foraging preferences and organisation of foraging labour in Asian honey bees.

ecology↗

bioRxiv2026

Host-specific and common core microbiota in adult butterflies across continents

1 Abstract The assembly of host-specific microbiota is critical for health and functioning of many insect pollinators. While social pollinators maintain core microbiota through social transmission, the factors driving microbiota assembly in solitary pollinators remain poorly understood. Lepidoptera are an important group of pollinators, but microbiome research has largely focused on their larval stage, while nectar-feeding adults have been widely ignored. Field-based studies of the adult butterfly microbiota are rare and geographically and taxonomically restricted. Here, we characterize the microbiota of adult butterflies from natural environments along elevational and seasonal gradients across two continents spanning the Neotropical and Palearctic realms. Microbiota diversity and composition were primarily explained by host taxonomic identity, whereas geographic location and temperature had little effect. We found high microbial titers and a common core microbiota across seven butterfly subfamilies from temperate and tropical regions. A comparison with sympatric wild bees revealed partial taxonomic overlap but marked distinctions in lactic acid bacteria between Lepidoptera and Hymenoptera. Together, our results demonstrate that host taxonomic identity, rather than environmental drivers, is the dominant force structuring the microbiota of adult butterflies. This highlights that the host-filtering capacity of solitary species has been largely underestimated, challenging previous assumptions that the microbiota of this important pollinator group is primarily environmentally driven and of limited functional significance.

ecology↗

bioRxiv2025

Experimental enhancement of structural heterogeneity in forest landscapes promotes multidimensional hoverfly diversity.

O_LIThe homogenization of temperate forests due to intensive management has led to biodiversity loss at local and landscape scales, threatening species persistence and ecosystem functions. However, experimental evidence on how structural heterogeneity among forest patches influences diversity at the landscape scale is lacking. Here, we test whether enhancing structural heterogeneity, via diverse deadwood enrichment and canopy gap creation treatments (Enhancement of Structural Beta Complexity, ESBC), can increase hoverfly diversity within landscapes, and elucidate the contributions of local (-) diversity enrichment and turnover ({beta}-diversity) to this effect. C_LIO_LIWe conducted a large-scale forest experiment in 11 regions across Germany. Each region included two districts, representing small forest landscapes. In one district, we implemented patches with ESBC treatments, while in the other, serving as the control, we established patches without ESBC. Hoverflies were sampled in three seasonal intervals and across, in total, 234 forest patches (50 x 50 m) using pan traps. We applied a new integrative meta-analytic framework that incorporates sample completeness to quantify taxonomic, functional, and phylogenetic diversity (TD, FD, PD) using Hill numbers at , {beta}, and {gamma} scales. C_LIO_LIAll three {gamma}-diversity dimensions - TD, FD, and PD - were significantly higher in structurally heterogeneous forest landscapes than in homogeneous ones. The strongest effects were observed for TD, indicating functional and phylogenetic redundancy among species. Effect sizes declined with increasing order of Hill numbers, suggesting that rare species benefit most from structural heterogeneity. C_LIO_LIIn most regions, {gamma}-diversity gains were driven by increases in -diversity rather than {beta}-diversity, highlighting the importance of interventions to increase local structural complexity. However, several regions also showed elevated {beta}-diversity, indicating context-dependent effects of spatial heterogeneity. C_LIO_LIOur results provide the first experimental evidence that enhancing structural heterogeneity at the landscape scale can restore multi-dimensional insect diversity in temperate forests. They underscore the management value of ESBC as a scalable tool to restore biodiversity, increase ecological resilience, and counteract biotic homogenization in production forests. C_LI

ecology↗

bioRxiv2025

A short cut to sample coverage standardization in meta-barcoding data provides new insights into land use effects on insect diversity

The use of metabarcoding for insect species identification has grown rapidly, but the absence of abundance data hinders meaningful diversity metrics like sample coverage-standardized species richness. Additionally, the vast number of taxa often lacks a unified phylogeny or trait database. We present a framework for constructing a phylogenetic tree encompassing the majority of insect families, standardisation of sample coverage (an objective measure of sample completeness) and assessment of both taxonomic and phylogenetic diversity using the Hill series for metabarcoding data. Applied to central Europe, our framework analysed insect diversity from 400 families along a land-use gradient. Results revealed land-use intensity significantly affects sample coverage, emphasizing the need for biodiversity standardization. After standardization, taxonomic diversity declined by 27-44%, and phylogenetic diversity by 13-29% across 39,000 Operational Taxonomic Units, from forests to agricultural areas. Rare species exhibited greater phylogenetic diversity loss than taxonomic, while dominant species showed smaller phylogenetic losses but stronger declines in taxonomic diversity. Our findings underscore agricultures detrimental effects on specific insect taxa, even after adjusting for sample coverage, and provide new insights into the loss of functional diversity, as represented by phylogeny.

ecology↗

bioRxiv2024

Swarming rate and timing of unmanaged honeybee colonies (Apis mellifera carnica) in a forest environment

Investigating the life history of social insect colonies and the demography of their populations are important for their conservation, but data collection is challenging. There is a growing interest in understanding the population status of wild-living honeybee colonies across Europe, for which it is critical to collect data on survival and natality rates. Although survival rates can be investigated through regular inspections of wild nests, the accurate quantification of natality rates (i.e., the number of swarms produced per colony per year) remains a significant challenge. Using digital weight scales, we remotely monitored the natural swarming behavior of ten unmanaged Apis mellifera carnica colonies housed in static-volume hives (45L) in a forest region of southern Germany. During the 2019 season, between mid-May and late June, we recorded 17 swarming events, averaging 1.7 swarms per colony. Our observations offer a reference point for the timing, frequency, and size of honeybee swarms that helps us understand the natural reproductive patterns of wild-living honeybees in a temperate forest environment.

ecology↗

bioRxiv2022

Reduced parasite burden in feral honeybee colonies

Bee parasites are the main threat to apiculture, and since many parasite taxa can spill over from honeybees (Apis mellifera) to other bee species, honeybee disease management is important for pollinator conservation in general. It is unknown whether honeybees that escaped from apiaries (i.e., feral colonies) benefit from natural parasite-reducing mechanisms like swarming or suffer from high parasite pressure due to the lack of medical treatment. In the latter case, they could function as parasite reservoirs and pose a risk to the health of managed honeybees (spillback) and wild bees (spillover). We compared the occurrence of 18 microparasites among managed (N=74) and feral (N=64) honeybee colony samples from four regions in Germany using qPCR. We distinguished five colony types representing differences in colony age and management histories, two variables potentially modulating parasite prevalence. Besides strong regional variation in parasite communities, parasite burden was consistently lower in feral than in managed colonies. The overall number of detected parasite taxa per colony was lower, and Trypanosomatidae, chronic bee paralysis virus, and deformed wing viruses A and B were less prevalent and abundant in feral colonies than in managed colonies. Parasite burden was lowest in newly founded feral colonies, intermediate in overwintered feral colonies and managed nucleus colonies, and highest in overwintered managed colonies and hived swarms. Our study confirms the hypothesis that the natural mode of colony reproduction and dispersal by swarming temporally reduces parasite pressure in honeybees. We conclude that feral colonies are unlikely to contribute significantly to the spread of bee diseases.

ecology↗

bioRxiv2022

Landscape diversity and local temperature, but not climate, affect arthropod predation among habitat types

Arthropod predators are important for ecosystem functioning by providing top-down regulation of insect herbivores. As predator communities and activity are influenced by biotic and abiotic factors on different spatial scales, the strength of top-down regulation ( arthropod predation) is also likely to vary. Understanding the combined effects of potential drivers on arthropod predation is urgently needed with regard to anthropogenic climate and land-use change. In a large-scale study, we recorded arthropod predation rates using artificial caterpillars on 113 plots of open herbaceous vegetation embedded in contrasting habitat types (forest, grassland, arable field, settlement) along climate and land-use gradients in Bavaria, Germany. As potential drivers we included habitat characteristics (habitat type, plant species richness, local mean temperature and mean relative humidity during artificial caterpillar exposure), landscape diversity (0.5-3.0-km, six scales), climate (multi-annual mean temperature, MAT) and interactive effects of habitat type with other drivers. We observed no substantial differences in arthropod predation rates between the studied habitat types, related to plant species richness and across the Bavarian-wide climatic gradient, but predation was limited when local mean temperatures were low and tended to decrease towards higher relative humidity. Arthropod predation rates increased towards more diverse landscapes at a 2-km scale. Interactive effects of habitat type with local weather conditions, plant species richness, landscape diversity and MAT were not observed. We conclude that landscape diversity favours high arthropod predation rates in open herbaceous vegetation independent of the dominant habitat in the vicinity. This finding may be harnessed to improve top-down control of herbivores, e.g. agricultural pests, but further research is needed for more specific recommendations on landscape management. The absence of MAT effects suggests that high predation rates may occur independent of moderate increases of MAT in the near future.

ecology↗

bioRxiv2021

Disentangling effects of climate and land use on biodiversity and ecosystem services - a multi-scale experimental design

O_LIClimate and land-use change are key drivers of environmental degradation in the Anthropocene, but too little is known about their interactive effects on biodiversity and ecosystem services. Long-term data on biodiversity trends are currently lacking. Furthermore, previous ecological studies have rarely considered climate and land use in a joint design, did not achieve variable independence or lost statistical power by not covering the full range of environmental gradients. C_LIO_LIHere, we introduce a multi-scale space-for-time study design to disentangle effects of climate and land use on biodiversity and ecosystem services. The site selection approach coupled extensive GIS-based exploration and correlation heatmaps with a crossed and nested design covering regional, landscape and local scales. Its implementation in Bavaria (Germany) resulted in a set of study plots that maximizes the potential range and independence of environmental variables at different spatial scales. C_LIO_LIStratifying the state of Bavaria into five climate zones and three prevailing land-use types, i.e. near-natural, agriculture and urban, resulted in 60 study regions covering a mean annual temperature gradient of 5.6-9.8 {degrees}C and a spatial extent of 380x360 km. Within these regions, we nested 180 study plots located in contrasting local land-use types, i.e. forests, grasslands, arable land or settlement (local climate gradient 4.5-10 {degrees}C). This approach achieved low correlations between climate and land-use (proportional cover) at the regional and landscape scale with |r [≤]0.33| and |r [≤]0.29|, respectively. Furthermore, using correlation heatmaps for local plot selection reduced potentially confounding relationships between landscape composition and configuration for plots located in forests, arable land and settlements. C_LIO_LIThe suggested design expands upon previous research in covering a significant range of environmental gradients and including a diversity of dominant land-use types at different scales within different climatic contexts. It allows independent assessment of the relative contribution of multi-scale climate and land use on biodiversity and ecosystem services. Understanding potential interdependencies among global change drivers is essential to develop effective restoration and mitigation strategies against biodiversity decline, especially in expectation of future climatic changes. Importantly, this study also provides a baseline for long-term ecological monitoring programs. C_LI

ecology↗

bioRxiv2021

Climate, latitude, and land cover predict flying insect biomass across a German malaise trap network

O_LIAmong the many concerns for biodiversity in the Anthropocene, recent reports of flying insect loss are particularly alarming, given their importance as pollinators and as a food source for many predators. Few insect monitoring programs cover large spatial scales required to provide more generalizable estimates of insect responses to global change drivers. C_LIO_LIWe ask how climate and surrounding habitat affect flying insect biomass and day of peak biomass using data from the first year of a new standardized distributed monitoring network at 84 locations across Germany comprising spatial gradient of land-cover types from protected to urban areas. C_LIO_LIFlying insect biomass increased linearly with monthly temperature across Germany. However, the effect of temperature on flying insect biomass flipped to negative in the hot months of June and July when local temperatures most exceeded long-term averages. C_LIO_LILand-cover explained little variation in insect biomass, but biomass was lowest in forested sites. Grasslands, pastures and orchards harbored the highest insect biomass. The date of peak biomass was primarily driven by surrounding land-cover type, with grasslands especially having earlier insect biomass phenologies. C_LIO_LIStandardized, large-scale monitoring is pivotal to uncover underlying processes of insect decline and to develop climate-adapted strategies to promote insect diversity. In a temperate climate region, we find that the benefits of temperature on flying insect biomass diminish in a German summer at locations where temperatures most exceeded long-term averages. These results highlighting the importance of local adaptation in climate change-driven impacts on insect communities. C_LI

ecology↗

bioRxiv2020

CRISPR/Cas9 mediated mutations as a new tool for studying taste in honeybees

BackgroundHoneybees rely on nectar as their main source of carbohydrates [1]. Sucrose, glucose and fructose are the main components of plant nectars [2] [3]. Intriguingly, honeybees express only three putative sugar receptors (AmGr1, AmGr2 and AmGr3) [4], which is in stark contrast to many other insects and vertebrates. The sugar receptors are only partially characterized [5] [6]. AmGr1 detects different sugars including sucrose and glucose. AmGr2 is assumed to act as a co-receptor only, while AmGr3 is assumedly a fructose receptor. ResultsWe show that honeybee gustatory receptor AmGr3 is highly specialized for fructose perception when expressed in Xenopus oocytes. When we introduced nonsense mutations to the respective AmGr3 gene using CRISPR/Cas9 in eggs of female workers, the resulting mutants displayed almost a complete loss of responsiveness to fructose. In contrast, responses to sucrose were normal. Nonsense mutations introduced by CRISPR/Cas9 in honeybees can thus induce a measurable behavioural change and serve to characterize the function of taste receptors in vivo. ConclusionCRISPR/Cas9 is an excellent novel tool for characterizing honeybee taste receptors in vivo. Biophysical receptor characterisation in Xenopus oocytes and nonsense mutation of AmGr3 in honeybees unequivocally demonstrate that this receptor is highly specific for fructose. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=166 HEIGHT=200 SRC="FIGDIR/small/009696v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@1100f07org.highwire.dtl.DTLVardef@14ac138org.highwire.dtl.DTLVardef@d37468org.highwire.dtl.DTLVardef@7f6abb_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 0C_FLOATNO C_FIG

genetics↗