Small Bee Species Research Articles

Transect walks and malaise traps differ in temperature sensitivity but reveal consistent drivers of pollinator richness

Abstract While transect walks have long been the preferred monitoring method for many flying insect taxa, malaise traps combined with DNA metabarcoding have gained growing prominence. However, it remains unclear whether both methods reveal comparable species richness and the same ecological drivers along environmental gradients. We selected three groups of pollinators (wild bees, hoverflies and butterflies) and one group of herbivores (grasshoppers) as functionally important and conservation‐relevant model groups, comparing results of both methods along an elevational gradient in the German Alps. Across the study region, both methods detected a similarly high species richness of pollinators with ~50% overlap of species pools, but transect walks revealed more species per site, especially in higher elevations and under low temperatures. Body size spectra differed between methods, with on average more large butterfly and more small bee species in transect walks. Nevertheless, temperature and flower richness were consistent drivers of pollinator richness, independent of the sampling method. Grasshopper richness from transect walks was considerably higher than from malaise traps. Both methods identified temperature and only malaise traps also identified management as drivers of grasshopper richness. We conclude that malaise traps are principally suitable substitutes for the more time‐consuming pollinator transect walks. However, the effectiveness of these passive traps is more susceptible to changes in sampling temperature, and in some pollinator groups, body size classes are presented differently, which is important to consider during analyses. For grasshoppers, transect walks appear to be more suitable to assess species richness, as considerably more species can be monitored.

Decline in wild bee species richness associated with honey bee (Apis mellifera L.) abundance in an urban ecosystem.

The spatial heterogeneity of urban landscapes, relatively low agrochemical use, and species-rich floral communities often support a surprising diversity of wild pollinators in cities. However, the management of Western honey bees (Apis mellifera L.) in urban areas may represent a new threat to wild bee communities. Urban beekeeping is commonly perceived as an environmentally friendly practice or a way to combat pollinator declines, when high-density beekeeping operations may actually have a negative influence on native and wild bee populations through floral resource competition and pathogen transmission. On the Island of Montréal, Canada there has been a particularly large increase in beekeeping across the city. Over the years following a large bee diversity survey ending in 2013, there was an influx of almost three thousand honey bee colonies to the city. In this study, we examined the wild bee communities and floral resources across a gradient of honey bee abundances in urban greenspaces in 2020, and compared the bee communities at the same sites before and after the large influx of honey bees. Overall, we found a negative relationship between urban beekeeping, pollen availability, and wild bee species richness. We also found that honey bee abundance had the strongest negative effect on small (inter-tegular span <2.25 mm) wild bee species richness. Small bee species may be at higher risk in areas with abundant honey bee populations as their limited foraging range may reduce their access to floral resources in times of increased competition. Further research on the influence of urban beekeeping on native and wild pollinators, coupled with evidence-based beekeeping regulations, is essential to ensure cities contain sufficient resources to support wild bee diversity alongside managed honey bees.

Andrena semirugosa brassicae (Hymenoptera: Andrenidae) as a major small bee species in apple orchards in Japan

Andrena semirugosa brassicae (Hymenoptera: Andrenidae) as a major small bee species in apple orchards in Japan

Variation of Small and Large Wild Bee Communities Under Honeybee Pressure in Highly Diverse Natural Habitats

During the study, the honeybee effects on wild bees were tested and hypothesized that smaller distances from beehives will increase competitions between honeybees and wild bees, while greater distances will have a deleterious effect on competition. The impact on species richness and diversity was tested with distances from beehives, considering that this may differ when large and small wild bee species are considered separately. Altogether 158 species and 13,164 individuals were collected, from which 72% (9,542 individuals) were Apis mellifera. High variation in abundances was detected from one year to another, and the species turnover by sites was 67% in site A, 66% in site V, and 63% in site F. This last one was the site with the previous contact with honeybees. Considering distances from beehives, significant decreases in small bee species diversity were detected from one year to another at each distance except site F, 250 m from hives. The changes in species diversity and community structure of small bee species are detected from one year to another.

Turnover in bee species composition and functional trait distributions between seasons in a tropical agricultural landscape

A comprehensive understanding of how spatial variation across landscapes regulates local abundances and species richness also needs to consider possible temporal changes in such relationships. In many tropical areas, the contrast between dry and rainy season is pronounced and the types and distributions of the main floral resources differ (herbs vs trees). This shift in resources could result in different pollinator abundances, species richness and trait compositions between seasons, as well as in how these components are spatially distributed. We compared the bee species composition between dry and rainy season in an agricultural mosaic landscape in southwestern Ethiopia, and analyzed it in relation to forest cover. We sampled bees for 67 days in the dry season and 86 days in the rainy season with pan and vane traps in 28 homegardens covering a gradient from low to high tree cover in the surrounding area. We found a clear shift in species composition between seasons, with more small bee species and more below-ground nesting bees in the rainy season compared to the dry season. The distribution of height at which the bees were foraging shifted between seasons with a higher proportion of the bees foraging at tree level in the dry season. Bee abundance and richness were generally positively affected by higher forest cover surrounding the homegardens, but there were no clear interaction effects between seasons, in contrast to our hypothesis. The clear turnover in species composition between seasons and the positive effect of forest cover show that mechanisms acting both at spatial and temporal scales are important in regulating local bee communities.

Evidence of forage distance limitations for small bees (Hymenoptera: Apidae)

The distribution of ground-nesting bees was investigated using transects of water traps in a mosaic of nesting and forage habitats at Shotover Hill in Oxfordshire, UK. The site includes a large area of ground-nesting bee activity and is adjoined on three sides by floristic hay meadows. This study showed that the females of small bee species (< 1.5 mm intertegular span) that were foraging in the hay meadows demonstrated a functional limitation to their homing range. The abundance of small bees declined rapidly with increasing distance from areas of high density nesting; declining more rapidly than might be expected from uniform dispersal into the surrounding landscape. By modelling the occurrence of bees along each transect it was found that the probability of observing a small bee in the hay meadows was reduced to 10% at a distance of 250-370 m from the nesting habitat. The result emphasises the scale on which habitat fragmentation will begin to impact upon bee diversity, and the relative contribution of managed pollen and nectar strips to areas of nesting habitat.

Roles of scale, matrix, and native habitat in supporting a diverse suburban pollinator assemblage

Wild pollinators provide important services to both wild and human-dominated ecosystems, yet this group may be threatened by widespread anthropogenic landscape change. Suburban sprawl is one of the fastest growing types of land use change in North America, and it has certain characteristics, such as abundant floral resources, that may be beneficial for many pollinators. We examined the effects of sprawl on the wild bee assemblage of the shortgrass steppe on the Front Range of Colorado, USA. Diversity, abundance, and community composition of bees in remnant grassland fragments surrounded by suburban residential land use were compared with those in extensive, continuous grassland. No overall effect of suburbanization on bee abundance was observed, and abundance was extremely variable even within study sites. Bee species richness was positively but nonlinearly related to grassland habitat area. Bee species density was higher and more variable in suburban sites. Suburban sites and smaller habitat area were both related to relative increases in the proportions of small bee species, social bees, and solitary cavity-nesting bees in the assemblage; small suburban habitat areas also favored species of the family Halictidae over Apidae, and individuals of the genus Halictus over those of the genus Lasioglossum. In this landscape, large native habitat areas surrounded by suburban sprawl may actually increase species richness and species density over that of continuous grassland, probably by means of habitat complementation or supplementation between grassland remnants and the surrounding suburban matrix. However, at habitat areas < 20 ha, species richness became quite variable; sites < 8 ha contained less than half the species of controls.

Local and landscape effects on bee communities of Hungarian winter cereal fields

1 Pollination is a key ecosystem service. Although bees are the most important pollinators, they are endangered by intensive agricultural practices. The present study investigated the effects of farmland management and environmental factors at local and landscape scales on bees in Central Hungary. 2 Bees were sampled in winter cereal fields that varied in the amount of applied fertilizer and insecticide use. Measurements included total, small and large bee species richness and abundance; stability of total species richness and abundance (coefficient of variation, CV); the nitrogen content of fertilizers; the number of insecticide applications; within-field location; species richness and abundance of insect-pollinated plants; and the percentage of semi-natural areas in a 500-m radius circle around the fields under study. 3 Increasing the amount of fertilizer decreased total and small bee abundance and increased the CV of total bee abundance. Insecticide use had a significant negative effect on total and small bee species richness and on large bee abundance. The percentage of semi-natural habitats in a 500-m radius did not influence bee species richness and abundance. 4 The results obtained confirms that the intensification of farmland management poses a threat to bee diversity, and thus may reduce pollination services. Recently-introduced agri-environment schemes are one potential approach for managing agricultural land use: reduced amounts of fertilizer and a cessation of insecticide application might lead to high bee species richness and abundance and ensure the pollination of wild plants and flowering crops.

Maximum foraging ranges in solitary bees: only few individuals have the capability to cover long foraging distances

Abstract To preserve populations of endangered bee species, sound knowledge of their maximum foraging distance between nest and host plants is crucial. Previous investigations predicted maximum foraging distances of 100–200 m for small bee species and up to 1100 m for very large species based on mainly indirect methods. The present study applied a new and direct approach to experimentally investigate maximum foraging distances in solitary bees. One endangered and two common species of different body sizes, all of which restrict pollen foraging to a single plant genus, were established in a landscape lacking their specific host plants. Females were forced to collect pollen on potted host plants that were successively placed in increasing distance from fixed nesting stands. The maximum foraging distance recorded for the small Hylaeus punctulatissimus was 1100 m, for the medium sized Chelostoma rapunculi 1275 m and for the large Hoplitis adunca 1400 m, indicating that maximum foraging distances at species level have been underestimated. However, the capability to use resources on such a large spatial scale applied only to a small percentage of individuals as 50% of the females of H. punctulatissimus and H. adunca did not forage at distances longer than 100–225 m and 300 m, respectively. This finding suggests that a close neighbourhood of nesting and foraging habitat within few hundred meters is crucial to maintain populations of these species, and that threshold distances at which half of the population discontinues foraging are a more meaningful parameter for conservation practice than the species specific maximum foraging distances.

Diversity and abundance of bees (Hymenoptera: Apiformes) in native and ruderal grasslands of agriculturally dominated landscapes

This study examined bee communities by sweep-net and pan-trap sampling and quantified the number of ramets of floral resources in native tallgrass prairie fragments and nearby ruderal areas (within 2.1 km) in Iowa, USA in the summer of 2004. Bee communities in ruderal areas were significantly less diverse than those in native tallgrass prairie remnants, with about half as many species and approximately a third as many bees. Diversity, abundance, and richness of floral resources were also significantly less in ruderal grasslands than in native prairies, indicating that poor floral resource levels may substantially depauperate their bee communities. Common bees dominated the composition of the ruderal grasslands; only one rare species in this study was found at a ruderal site, indicating that high-quality prairie remnants are important reservoirs of bee diversity. Abundance of flowering ramets of a plant species was a significant predictor of the abundance of bees found on that plant. There was also a preference for human-yellow flowers after adjusting for ramet abundance and there were significantly more bees caught in yellow pan traps than blue or white ones. The abundance, but not the richness, of small bee species (length ≤ 7.5 mm) was less than expected at ruderal sites when compared to prairies, implying the presence of local nesting opportunities in ruderal grasslands for small bees but insufficient resources to support large populations.