Abundance Of Hoverflies Research Articles

Effect of Sinapis alba L. as an Insectary Plant on the Occurrence of Aphis fabae Scop., Coccinellidae and Syrphidae in Broad Bean

Introducing insectary plants along with principal crops is an effective way to increase the biological diversity of beneficial insects and improve the stability of ecological equilibrium in agrocenoses and could be an alternative to chemical plant protection, particularly in organic farming. The goal of this study was to determine the effect of white mustard as a companion plant in broad bean cultivation on the occurrence of Aphis fabae Scop., Syrphidae, and Coccinellidae. The study also aimed at finding the optimum row separation of broad bean plants. It also evaluated the effectiveness of the thinning of mustard in a specific time to eliminate excessive competition with the main crop. The results showed that white mustard contributed to visible suppression of A. fabae abundance on broad bean (to the level similar as with the use of chemical protection). S. alba contributed to an increased abundance of hoverflies and lady beetles on broad bean despite the relatively low abundance of their prey, i.e., aphids. Mustard thinning positively affected abundance of larvae and adults of lady beetles as well as improved predator-prey ratio for hoverfly larvae and adult lady beetles. The most appropriate distance between broad bean rows when white mustard was introduced was 65 cm, with the concomitant conduct of mustard thinning when the broad bean plants reached flower bud formation. White mustard can be recommended as an element increasing the role of natural enemies of aphids in mixed crops, however, its strong growth should be taken into account and the plant density should be properly adjusted to avoid excessive competition with main plant.

Time since establishment drives bee and hoverfly diversity, abundance of crop-pollinating bees and aphidophagous hoverflies in perennial wildflower strips

Wildflower strips (WFS) are amongst the most commonly applied measures to promote pollinators and natural enemies of crop pests in agroecosystems. Their potential to enhance these functionally important insect groups may vary substantially with time since establishment of WFS. However, knowledge on their temporal dynamics remains scarce, hampering recommendations for optimized design and management. We therefore examined temporal dynamics of taxonomic and functional groups of bees and hoverflies in perennial WFS ranging from one to ≥6 years since sowing with a standardized species-rich seed mixture of flowering plants in 18 agricultural landscapes in Switzerland. The abundance of wild bees, honeybees and hoverflies declined after the second year by 89%, 62% and 72%, respectively. Declines in bee abundance and hoverfly species richness were linear and those of aphidophagous hoverflies exponential, while wild bee species richness peaked in the third year. Declines over time generally paralleled decreases in flower abundance (-83%) and flowering species richness (-61%) and an increase in grass cover (+70%) in WFS. Flowering plant species richness showed strong positive relationships with dominant crop-visiting wild bees and aphidophagous hoverflies. Furthermore, dominant crop-visiting wild bees, but not aphidophagous hoverflies, were positively related to the proportion of (semi-)open semi-natural habitat in the surrounding landscape (500 m radius), but negatively with forest. We conclude that the effectiveness of perennial WFS to promote pollinator diversity, crop-pollinating bees and aphidophagous hoverflies through foraging resources decreases after the first two to three years, probably due to a decline of diverse and abundant floral resources. Although older perennial WFS may still provide valuable nesting and overwintering opportunities for pollinators and natural enemies, our findings indicate that regular re-sowing of perennial WFS may be necessary to maintain adequate floral resource provisioning for effective pollinator conservation and promotion of crop pollination and natural pest control services in agricultural landscapes.

Pollinator sampling methods influence community patterns assessments by capturing species with different traits and at different abundances

In order to synthesize changes in pollinating insect communities across space and time, it is necessary to understand whether, and how, sampling methods influence assessments of community patterns. We compared how two common sampling methods—yellow combined flight traps and net sampling—influence our understanding of the species richness, abundance and composition of wild bees and hoverflies, and addressed whether these patterns resulted from potentially biased sampling of individuals or species with different types of functional traits. We sampled bee and hoverfly communities in six sites over three seasons in Saxony-Anhalt, Germany. We captured more species and individuals of bees with traps and more species and individuals of hoverflies with net sampling. However, rarefied richness results were less dramatic between the sampling methods for bees and were not different between the sampling methods for hoverflies. Thus, differences in species richness across sampling methods were mostly due to differences in the number of individuals captured in the different methods. We captured more small-sized bees and hoverflies with traps. We tested if the different methods collected individuals and species with different functional traits, such as nesting preferences, sociality and flower specialization for bees and floral preference, migratory status and habitat preference for hoverflies. For most traits, we collected more individuals but not more species with a certain trait in the different methods. This was mainly due to a high abundance of one species being collected in the different methods. These results suggest that the best methodology depends on the aim of the survey, and that the methods cannot be easily combined into synthesis research. Our results have implications for the development of monitoring schemes for pollinators and for synthesis of trends that can identify threats to pollinators and inform research of pollinator conservation strategies.

Distribution and pollination services of wild bees and hoverflies along an altitudinal gradient in mountain hay meadows.

Extensively managed and flower‐rich mountain hay meadows, hotspots of Europe's biodiversity, are subject to environmental and climatic gradients linked to altitude. While the shift of pollinators from bee‐ to fly‐dominated communities with increasing elevation across vegetation zones is well established, the effect of highland altitudinal gradients on the community structure of pollinators within a specific habitat is poorly understood. We assessed wild bee and hoverfly communities, and their pollination service to three plant species common in mountain hay meadows, in eighteen extensively managed yellow oat grasslands (Trisetum flavescens) with an altitudinal gradient spanning approx. 300 m. Species richness and abundance of pollinators increased with elevation, but no shift between hoverflies and wild bees (mainly bumblebees) occurred. Seedset of the woodland cranesbill (Geranium sylvaticum) increased with hoverfly abundance, and seedset of the marsh thistle (Cirsium palustre) increased with wild bee abundance. Black rampion (Phyteuma nigrum) showed no significant response. The assignment of specific pollinator communities, and their response to altitude in highlands, to different plant species underlines the importance of wild bees and hoverflies as pollinators in extensive grassland systems.

Insect biomass decline scaled to species diversity: General patterns derived from a hoverfly community

Reports of declines in biomass of flying insects have alarmed the world in recent years. However, how biomass declines reflect biodiversity loss is still an open question. Here, we analyze the abundance (19,604 individuals) of 162 hoverfly species (Diptera: Syrphidae), at six locations in German nature reserves in 1989 and 2014, and generalize the results with a model varying decline rates of common vs. rare species. We show isometric decline rates between total insect biomass and total hoverfly abundance and a scale-dependent decline in hoverfly species richness, ranging between -23% over the season to -82% at the daily level. We constructed a theoretical null model to explore how strong declines in total abundance translate to changing rank-abundance curves, species persistence, and diversity measures. Observed persistence rates were disproportionately lower than expected for species of intermediate abundance, while the rarest species showed decline and appearance rates consistent with random expectation. Our results suggest that large insect biomass declines are predictive of insect diversity declines. Under current threats, even the more common species are in peril, calling for a reevaluation of hazards and conservation strategies that traditionally target already rare and endangered species only.

Non-rotational set-aside fields improve reproductive success of cavity-nesting bees and wasps at the landscape scale, but have no effect on other wild bees and hoverflies in mid-summer

Wild bees, hoverflies and wasps are valuable ecosystem service providers in agricultural systems through pollination and biological control, and their species richness, abundance and reproductive success well indicate ecosystem health. However, they are often limited by foraging and nesting resources that are major drivers behind their steep decline. Although agri-environmental measurements improve resources for these groups, their wider landscape-scale impacts are basically unknown. Here, we questioned whether 2–3 years old, sown set-aside fields could have a potential in enhancing pollinator and predatory wasp communities at the landscape scale in a Central European agroecosystem. We measured reproductive success and parasitism of cavity-nesting bees and wasps by trapnests throughout the vegetation period, and sampled bee and hoverfly communities by colored pan traps in mid-summer, comparing landscapes with and without set-aside fields. We measured the effects of increasing distance from set-aside fields, the effects of share of different habitats and flower resources, and the effects of increasing set-aside field percentage area at landscape scale. The landscape scale effects of set-aside fields varied among taxa and/or at different time scales. Reproductive success of cavity-nesting bees and wasps was positively related to the presence of set-aside fields in the landscape and together with the number of cavity-nesting bee and wasp genera increased with the proportion of set-aside fields. Species richness or abundance of bees or hoverflies showed no difference between landscape plots with or without set-aside fields in the mid-summer period according to the pan trap samples, and flower abundance and distance from the set-aside fields had only a limited effect. Set-aside fields had no effect on either the most abundant wild bee species or on composition of species of intermediate abundance. Our results suggest that reproductive success of cavity-nesting bees and wasps can be enhanced by additional flower resources and nesting habitats through set-aside fields at the landscape scale. Other wild bees and hoverflies can be less sensitive to the presence of set-aside fields according to our results that might need different conservation approaches. But this might also suggest that such landscape-scale benefits of set-aside field management might be measureable only with samplings covering the whole vegetation period. We argue that well-defined measures specific to spatial scale and target groups are mandatory and should be adapted to the different histories and local contexts of agricultural landscapes in Europe to strengthen ecosystem service provider insects and have the highest benefit for agricultural production.

Habitat loss and degradation due to farming intensification modify the floral visitor assemblages of a semiarid keystone shrub

The expansion of intensive agriculture has severely altered landscapes, a process that has been aggravated by the increase of greenhouse agriculture. However, few studies have considered the combined effects of habitat loss/degradation and greenhouse farming on insect visitors to native plants. We analysed how habitat loss/degradation and greenhouse farming are related to the composition, abundance, and richness of the insect assemblages visiting flowers in a semiarid keystone shrub (Ziziphus lotus) in southeast Spain, home to Europe's largest area of greenhouses. We studied 21 populations distributed across a gradient of greenhouse intensification and habitat loss. The composition, abundance, and richness of the Ziziphus insect assemblage substantially varied between populations and were differently affected by natural habitat‐remnant and landscape degradation and population isolation. Insect abundance was negatively affected by habitat loss at population level but positively affected at individual Ziziphus scale. Honey‐bee relative abundance increased in highly degraded landscapes and isolated populations, being positively associated with hoverflies and negatively with ants and bee‐flies. Wild bees, carrion flies, and wasps remain neutral along the degradation axes. Insect visitor abundance per plant affected positively the flower visitation rate, which was also favoured by the relative abundance of honey bees, wild bees, and hoverflies. Species richness was not influenced by anthropogenic degradation, and did not affect flower visitation rate. Our results highlight the fragility of wild pollinator communities to landscape and habitat degradation, and the need to regulate intensive farming practices to preserve wild insect pollinator assemblages in semiarid habitats.

The relative importance of green infrastructure as refuge habitat for pollinators increases with local land‐use intensity

Abstract Agricultural expansion and intensification have resulted in strong declines in farmland biodiversity across Europe. In many intensively farmed landscapes, linear landscape elements such as field boundaries, road verges and ditch banks are the main remaining green infrastructures providing refuge for biodiversity, and as such play a pivotal role in agri‐environmental policies aiming at mitigating biodiversity loss. Yet, while we have a fairly good understanding of how agricultural intensification influences biodiversity on farmland, little is known about whether and how local land‐use intensity affects biodiversity in nearby linear landscape elements and how this affects their role as biodiversity refuge. Focussing on pollinating insects, we examined the effects of local land‐use intensity on biodiversity in agricultural fields and adjacent green infrastructures. In an intensively farmed area in south‐western France, we selected 23 agricultural grasslands and nearby field boundaries along a gradient in grassland cutting frequency which acted as a proxy for land‐use intensity. We analysed how grassland cutting frequency affects species richness, abundance and community composition of wild bees and hoverflies in the grasslands and neighbouring field boundaries, and whether these effects differ across habitat types and species groups. Grassland cutting frequency negatively affected pollinator species richness and abundance in the grasslands, whereas pollinators in the neighbouring field boundaries were unaffected. These responses reflected the effects of cutting frequency on floral resources, with flower cover and richness decreasing in grasslands but not in field boundaries. As a result, the proportion of the local pollinator community supported by field boundaries increased with the increasing cutting frequency of the adjacent grassland. Common and rare pollinator species generally showed similar responses. Furthermore, communities of plants and pollinators in field boundaries next to intensively farmed grasslands were fairly similar to those next to extensively farmed ones. Synthesis and applications. Our results suggest that, as nearby land use intensifies, flower‐rich field boundaries become increasingly important as pollinator refuge habitats. Conserving field boundaries and other green infrastructures, and maintaining or enhancing their quality, therefore constitute important tools to conserve and promote pollinators in intensively farmed landscapes.

Mass Seasonal Migrations of Hoverflies Provide Extensive Pollination and Crop Protection Services

Despite the fact that migratory insects dominate aerial bioflows in terms of diversity, abundance, and biomass [1-6], the migration patterns of most species, and the effects of their annual fluxes between high- and low-latitude regions, are poorly known. One important group of long-range migrants that remain understudied is a suite of highly beneficial species of hoverfly in the tribe Syrphini, which we collectively term "migrant hoverflies." Adults are key pollinators [7-10] and larvae are significant biocontrol agents of aphid crop pests [11], and thus, it is important to quantify the scale of their migrations and the crucial ecosystem services they provide with respect to energy, nutrient, and biomass transport; regulation of crop pests; and pollen transfer. Such assessments cannot be made by sporadic observations of mass arrivals at ground level, because hoverflies largely migrate unnoticed high above ground. We used insect-monitoring radars [12] to show that up to 4 billion hoverflies (80tons of biomass) travel high above southern Britain each year in seasonally adaptive directions. The long-range migrations redistribute tons of essential nutrients (nitrogen [N] and phosphorus [P]) and transport billions of pollen grains between Britain and Europe, and locally produced populations consume 6 trillion aphids and make billions of flower visits. Migrant hoverfly abundance fluctuated greatly between years, but there was no evidence of a population trend during the 10-year study period. Considering that many beneficial insects are seriously declining [7, 10, 13-19], our results demonstrate that migrant hoverflies arekey to maintaining essential ecosystem services.

Entomofauna associated with Avena sativa in southern Mato Grosso do Sul, Brazil

ABSTRACT This study was aimed at examining the composition of insects and fluctuations in their populations in Avena sativa in southern Mato Grosso do Sul. The study was carried out at the experimental farm of the Federal University of Grande Dourados (FAECA) in Dourados, Mato Grosso do Sul, in 2014 and 2015, in an area of three hectares divided into 80 plots of 169 m2 each. The assessments were carried out weekly by sampling the area within a 0.25-m2 metal frame, totaling ten evaluations. Within the frame, ten plants were examined for aphids and all plants were inspected for other insects. Based on the faunistic analysis (abundance, constancy, frequency, and dominance), eight species were observed during the two years of study. The most frequent, abundant, dominant, and recurring species were Rhopalosiphum padi, Spodoptera frugiperda and dipterans of the family Syrphidae (hoverfly). The population of R. padi increased until approximately the 40th day after emergence (DAE), when the highest abundance of hoverflies was also observed. After that, the population of R. padi decreased. The aphid R. padi was the main insect observed in A. sativa during the two years of study but were naturally controlled by hoverflies; therefore, chemical intervention was not needed.

Linear and non-linear effects of goldenrod invasions on native pollinator and plant populations

The increased introduction of non-native species to habitats is a characteristic of globalisation. The impact of invading species on communities may be either linearly or non-linearly related to the invaders’ abundance in a habitat. However, non-linear relationships with a threshold point at which the community can no longer tolerate the invasive species without loss of ecosystem functions remains poorly studied. We selected 31 wet meadow sites that encompassed the entire coverage spectrum of invasive goldenrods, and surveyed the abundance and diversity of pollinating insects (bees, butterflies and hover flies) and native plants. The species richness of native plants decreased linearly with goldenrod cover, whereas the abundance and species richness of bees and butterflies decreased non-linearly with increasing goldenrod cover. However, no statistically significant changes across goldenrod cover were noted for the abundance and species richness of hover flies. Because of the non-linear response, goldenrod had no visible impact on bees and butterflies until it reached cover in a habitat of about 50% and 30–40%, respectively. Moreover, changes driven by goldenrod in the plant and pollinator communities were related to species loss rather than species replacement. We demonstrated that the impact of goldenrod cover on a habitat is not instantaneous. Habit management aimed at preventing the invasion process and alleviating its impact should take into account that, for the non-linear relationships, the negative impact can appear rapidly after crossing the threshold point.

Flower Strips in Wheat Intercropping System: Effect on Pollinator Abundance and Diversity in Belgium.

The decline of pollinators in agricultural areas has been observed for some decades, this being partly due to landscape simplification in intensive agrosystems. Diversifying agricultural landscapes by sowing flower strips within fields could reduce these adverse effects on biodiversity. In this context, the study presented here aimed at assessing and comparing the abundance and diversity of bees (Hymenoptera: Anthophila) and hoverflies (Diptera: Syrphidae) found and visiting flowers in three types of flower strips in Belgium: (i) a mixture of 11 wild flowers, (ii) a monofloral strip of Dimorphoteca pluvialis (Asteraceae) and (iii) a monofloral strip of Camelina sativa (Brassicaceae), where the last two are considered to be intercrops since they are valuable on the market, all sown within a field of winter wheat (Triticum aestivum L.). Pollinators were captured with pan traps and by netting in standardised transects from May to July 2017. One-thousand one-hundred and eighty-four individuals belonging to 43 bee species and 18 hoverfly species were collected. Significant differences in hoverfly diversity were found between the different flower strips. The multifloral treatment supported a greater diversity of syrphid species. Various pollinator species visited the different flowers composing the mixture and also D. pluvialis. The pollinator community proved to be predominantly generalist, with the exception of an oligolectic species in Belgium, Andrena nitidiuscula. Moreover, the three tested flower strips were effective in attracting hoverflies, among them natural enemies of insect pests. This study opens new perspectives in the design of intercropping systems with flower strips towards the design of sustainable agro-ecosystems. Improving economic profitability of sowing flower strips could encourage farmers to diversify their agricultural systems and foster conservation biology strategies.

Intensification of Ethiopian coffee agroforestry drives impoverishment of the Arabica coffee flower visiting bee and fly communities

Intensively managed shade coffee plantations are expanding in SW Ethiopia, at the cost of the more natural coffee agroforestry systems. Here, we investigated consequences for the potential pollinator community of Arabica coffee (Coffea arabica L.) in its natural range. We surveyed coffee flower visitors at six different sites in the Jimma region in SW Ethiopia, and compared species richness and abundance between semi-natural coffee forests and shaded coffee plantations. Overall, we found six bee (Hymenoptera: Anthophila) and twenty fly species (Diptera: Brachycera) visiting C. arabica flowers. Species richness and overall abundance of flower visitors was significantly higher in the semi-natural forests compared to the plantations. A significantly higher abundance of non-Apis bees and hoverflies (Syrphidae) visiting C. arabica flowers was observed in the semi-natural forest plots, but numbers for other Diptera and honeybees (Apis mellifera L.) did not differ significantly between the agroforestry systems. Our results show an impoverishment of the coffee flower visiting insect community in response to agricultural intensification. This suggests a functional shift of the coffee pollinator community and, hence, may influence the stability of the provided pollination ecosystem services and coffee yield in the long term. We did, however, not quantify pollination services in this study.

Associations between plant and pollinator communities under grassland restoration respond mainly to landscape connectivity

Abstract Land‐use change can disrupt associations between different trophic groups, but it is unclear if habitat restoration can recover these associations. In Sweden, restoration efforts have been applied to increase areas of semi‐natural grassland previously remaining as small fragments due to abandonment. We assessed how the associations between plant and pollinator communities can be modified by grassland abandonment and restoration, together with landscape connectivity. We surveyed plant, hoverfly and bee communities in 10 abandoned, 18 restored and 10 intact grasslands in south‐central Sweden, distributed along a gradient of isolation from other species‐rich grasslands. We assessed the effects of management history and connectivity on the relationships between several measures of the composition of plant and pollinator communities as well as between plant community composition and pollinator guilds. The composition of the local flowering plant community was an important determinant of both hoverfly and bee communities. However, plant‐pollinator associations were modulated by landscape connectivity and, to some extent, by grassland management history. Abundance, species richness and functional richness of bees and species richness of hoverflies were positively associated with local plant communities in isolated grasslands, but these associations weakened in well‐connected grasslands. In contrast, hoverfly abundance correlated positively with plant communities in well‐connected grasslands. The response of pollinator feeding guilds was consistent with overall pollinator communities. However, abundance of bees adapted to foraging on particular plants (long‐tongued and short‐tongued) responded positively to specific host plant species abundance. Synthesis and applications. Our results show how land use and landscape context can significantly affect interactions between different trophic levels. Land use and landscape context should therefore be recognised in grassland restoration guidelines. Enhancement of both functional‐rich and species‐rich plant communities, as well as increasing abundance and species and functional richness of host plants for specialist pollinators will amend pollinator diversity. Restoration actions should consider the spatial configuration of the landscape to improve its outcome. Efforts in more isolated grasslands should focus on promoting local habitat quality while, in more connected grasslands, the priority should be maintaining connectivity to well‐preserved grasslands.

Floral preferences of hoverflies (Diptera: Syrphidae) in response to the abundance and species richness of flowering plants

For understanding the relationship between floral resources and the abundance of hoverflies, five meadows were selected at different elevations in a forested region. At each site the number of flowering herbaceous plants was assessed along a transect at 10-m intervals. To measure floral density, we counted the number of open flowers per species in each plot. Hoverflies visiting flowering plants were captured in each plot during 10 minutes. Path analysis showed that there was a negative correlation between plant species richness and syrphid abundance. Flower abundance had a strong positive direct effect on syrphid abundance but had indirect effects on the number of syrphid species. Only altitude had a strong positive direct effect on the number of syrphid species and this may be explained by the different climatic conditions. Some plant species attracted more syrphids than others. There were significantly fewer species of hoverfly per plot with increasing numbers of flowers. We interpret this to mean that plant species with a high density of flowers attracted more syrphids of the same species. Analysis of pollen grains extracted from two species of hoverflies showed that flower constancy occurred in three examined sites.

Influence of urbanisation and plants on the diversity and abundance of aphids and their ladybird and hoverfly predators in domestic gardens

Urban gardens can harbour a high diversity of insects, which are critically important components of urban ecosystems. In this work, we investigate the richness and diversity of a major taxon of economic and ecological importance, the aphids (Homoptera: Aphididae), and their main insect predators, the hoverflies (Diptera: Syrphidae) and ladybirds (Coleoptera: Coccinellidae), in urban gardens. We examined how variation in environmental factors associated with urbanisation (garden host plant abundance, garden plant richness, garden size, proportion of impervious surfaces in the surrounding area) directly and indirectly (via prey and predator abundance) influence the local diversity and abundance of aphids, ladybirds, and hoverflies. Sixty-seven domestic gardens located in southern England were surveyed during the peak period of aphid abundance, and the numbers and identity of aphids and their predators were recorded. We observed 45 aphid species (179917 individuals in total), 15 hoverfly species (494 individuals) and 8 ladybird species (173 individuals). We found that aphid species richness and abundance were positively associated with utilised host plant abundance and garden plant species richness. Hoverfly abundance was positively correlated with garden plant richness. The abundance of ladybirds was positively correlated with aphid abundance and garden plant species richness, and negatively associated to the proportion of impervious surfaces in the surrounding environment. The difference in responses between the two major taxa of aphid predators may reflect differences in their behaviour and natural history. Our results indicate that overall increases in urban land cover are not favourable for ladybirds as a group, and that fine scale habitat variables that are determined by garden owners have the potential to greatly affect the general diversity of aphids and their main predators.

Contrasting responses in community structure and phenology of migratory and non‐migratory pollinators to urbanization

AbstractAimAnthropogenic landscape change, such as urbanization, can affect community structure and ecological interactions. Furthermore, changes in ambient temperature and resource availability due to urbanization may affect migratory and non‐migratory species differently. However, the response of migratory species to urbanization is poorly investigated, and knowledge for invertebrates in particular is lacking. Our aim was to investigate whether there was a shift in community structure and phenology of hoverflies in urban landscapes, depending on migratory status.LocationSwitzerland.MethodsUsing a paired design, we compared urban and rural landscapes to investigate the impact of urbanization on the abundance, diversity and phenology of hoverflies. Furthermore, we tested whether migratory and non‐migratory species responded differently to urbanization.ResultsWe observed a difference in the response of migratory and non‐migratory hoverfly communities. Although the abundance of hoverflies was higher in the rural ecosystem, driven by a high abundance of migratory species, there was no difference in species richness between the land use types. However, the community structure of non‐migratory species was significantly different between urban and rural ecosystems. The phenology of hoverflies differed between the two ecosystems, with an earlier appearance in the year of migratory species in urban landscapes.Main conclusionsTo our knowledge, this is the first study to investigate the response of migratory insect communities to urbanization. We demonstrated that migratory and non‐migratory hoverflies respond differently to urbanization. This highlights the importance of differentiating between trait and mobility groups to understand community assemblage patterns in anthropogenic landscapes. The differences in phenology supports the growing evidence that urbanization not only affects the phenology of vegetation, but also affects the higher trophic levels. Changes in the phenology and community composition of species as a result of anthropogenic landscape change may have important implications for the maintenance of key ecosystem functions, such as pollination.

Contrasting impacts of highly invasive plant species on flower-visiting insect communities

Invasive alien plants threaten biodiversity, ecosystems and service provision worldwide. They can have positive and negative direct and indirect effects on herbivorous insects, including those that provide pollination services. Here, we quantify how three highly invasive plant species (Heracleum mantegazzianum, Impatiens glandulifera and Fallopia japonica) influence the availability of floral resources and flower-visiting insect communities. We compared invaded with comparable uninvaded areas to assess floral resources and used pan-trapping to quantify insect communities. Only F. japonica influenced floral resource availability: sites invaded by this species had a higher flowering plant species richness and abundance of open floral units than uninvaded sites, probably due to its late flowering and the paucity of other flowering species at this time of year. Fallopia japonica was also associated with higher abundances of bumblebees, higher overall insect diversity and higher hoverfly diversity than uninvaded areas. Differences in pollinator communities were also associated with I. glandulifera and H. mantegazzianum, despite there being no detectable differences in floral resources at these sites. Specifically, there were more bumblebees and solitary bees in I. glandulifera sites, and a higher overall diversity of insects, particularly hoverflies. By contrast, H. mantegazzianum sites had a lower abundance of solitary bees and hoverflies. These findings confirm that invasive plant species have a range of species-specific effects on ecological communities. This supports the emerging view that control of invasive species, as required under international obligations, is not simple and that potential losses and gains for biodiversity must be carefully evaluated on a case-by-case basis.

Landscape complexity promotes hoverflies across different types of semi‐natural habitats in farmland

Abstract Semi‐natural habitats (SNH) provide essential resources for many organisms in agricultural landscapes and can increase biodiversity at the local and landscape scale. For the management of ecosystem services, it is crucial to understand how local characteristics of SNH and the surrounding landscape complexity affect beneficial species. We investigated this for hoverflies (Diptera: Syrphidae)—an important functional group providing both pest control and pollination services—in a total of 138 SNH within 35 agricultural landscapes in Switzerland and Germany. SNH differed in type (woody, herbaceous), shape (areal, linear) and availability of food resources (floral resources and aphids). They were located along a gradient of landscape complexity (1%–75% SNH in a 1 km radius). In total, 9,030 hoverflies belonging to 89 species were collected. In both countries, hoverfly community composition was mainly driven by SNH type and SNH shape, in addition to landscape complexity in Switzerland. Species richness of hoverflies increased with additional SNH at the landscape scale. However, the ubiquitous and dominant aphidophagous species Episyrphus balteatus was indifferent to landscape composition. Species richness of total and aphidophagous hoverflies was higher in woody than in herbaceous SNH. Hoverfly species richness was similar in linear and areal SNH, but non‐aphidophagous hoverflies were more vulnerable to landscape simplification in linear than areal SNH. Effects of the SNH type partly differed between the two countries. In Germany, the dominant aphidophagous species E. balteatus preferred woody over herbaceous SNH, while no such difference was found in Switzerland. Overall, local richness and abundance of floral resources were poor predictors for hoverfly abundance, richness or community composition. Synthesis and applications. Hoverfly species richness and community composition in semi‐natural habitats (SNH) were mainly driven by the SNH type and landscape complexity. Conservation and restoration of complex agricultural landscapes with a high proportion of different SNH types is therefore key for the conservation of hoverfly diversity, and thus likely to promote pest control and pollination services provided by them. Thereby, local improvement of SNH to promote hoverflies has to consider regional differences in habitat characteristics.

Composition and Seasonal Abundance of Hover Flies (Diptera: Syrphidae) at a Midelevation Site in Central Utah

Abstract Dipteran pollinators are important in the successful reproduction of many plants, yet are less studied than other groups. We know that these insects affect the biodiversity of natural landscapes, yet much remains unknown about the extent of their influence in pollination systems and flight seasons. In this study, we collected hover flies (Diptera: Syrphidae) with 3 Malaise traps at a midelevation site in central Utah throughout the flies' flight season of 2015. We collected 27 genera and 48 species in our traps. We determined seasonal flight times by collecting at weekly intervals throughout the frost-free year. Abundance of all hover flies peaked twice, in June and September, showing a bimodal distribution. We noted a drop in overall abundance during the hottest months of July and August. Species diversity and richness also peaked in June and September. We calculated species richness estimators, which suggest that more than 60 species make up the total assemblage at the study site. Local museum ...