Widespread Pollinators Research Articles

A Comparative Analysis of State Pollinator Protection Laws

Various states in the U.S. have passed laws to regulate pesticide use for agriculture and prohibit excessive harm to pollinators. However, current online public information on pollinator protection laws in America is largely lacking. This study establishes an inventory of the state legislation that has banned neonicotinoid pesticides and protected pollinators. The results of this review indicate that only sixteen states have enacted neonicotinoid bans, none of which are complete bans. Sixteen states had no portion of their agricultural website dedicated to pollinator conservation and did not address bees or pollinators at all except when referencing pest control. These same states had no legislation or ban on neonicotinoids. In sixteen states neonicotinoids are labeled as restricted use, however, finding information on neonicotinoid regulation and defining restricted use was difficult. Overall, there is a lack of clarity and consistency across state legislation. There are inconsistent policies across the U.S., but the states that have more progressive policies also are more conscious of the environment and conservation. The implementation of federal legislation would be most effective at unifying the states and creating widespread pollinator conservation.

Honeybee visitation to shared flowers increases Vairimorpha ceranae prevalence in bumblebees.

Vairimorpha (=Nosema) ceranae is a widespread pollinator parasite that commonly infects honeybees and wild pollinators, including bumblebees. Honeybees are highly competent V. ceranae hosts and previous work in experimental flight cages suggests V. ceranae can be transmitted during visitation to shared flowers. However, the relationship between floral visitation in the natural environment and the prevalence of V. ceranae among multiple bee species has not been explored. Here, we analyzed the number and duration of pollinator visits to particular components of squash flowers-including the petals, stamen, and nectary-at six farms in southeastern Michigan, USA. We also determined the prevalence of V. ceranae in honeybees and bumblebees at each site. Our results showed that more honeybee flower contacts and longer duration of contacts with pollen and nectar were linked with greater V. ceranae prevalence in bumblebees. Honeybee visitation patterns appear to have a disproportionately large impact on V. ceranae prevalence in bumblebees even though honeybees are not the most frequent flower visitors. Floral visitation by squash bees or other pollinators was not linked with V. ceranae prevalence in bumblebees. Further, V. ceranae prevalence in honeybees was unaffected by floral visitation behaviors by any pollinator species. These results suggest that honeybee visitation behaviors on shared floral resources may be an important contributor to increased V. ceranae spillover to bumblebees in the field. Understanding how V. ceranae prevalence is influenced by pollinator behavior in the shared floral landscape is critical for reducing parasite spillover into declining wild bee populations.

Recent and future declines of a historically widespread pollinator linked to climate, land cover, and pesticides

Recent and future declines of a historically widespread pollinator linked to climate, land cover, and pesticides

Recent and future declines of a historically widespread pollinator linked to climate, land cover, and pesticides

The acute decline in global biodiversity includes not only the loss of rare species, but also the rapid collapse of common species across many different taxa. The loss of pollinating insects is of particular concern because of the ecological and economic values these species provide. The western bumble bee (Bombus occidentalis) was once common in western North America, but this species has become increasingly rare through much of its range. To understand potential mechanisms driving these declines, we used Bayesian occupancy models to investigate the effects of climate and land cover from 1998 to 2020, pesticide use from 2008 to 2014, and projected expected occupancy under three future scenarios. Using 14,457 surveys across 2.8 million km2 in the western United States, we found strong negative relationships between increasing temperature and drought on occupancy and identified neonicotinoids as the pesticides of greatest negative influence across our study region. The mean predicted occupancy declined by 57% from 1998 to 2020, ranging from 15 to 83% declines across 16 ecoregions. Even under the most optimistic scenario, we found continued declines in nearly half of the ecoregions by the 2050s and mean declines of 93% under the most severe scenario across all ecoregions. This assessment underscores the tenuous future of B.occidentalis and demonstrates the scale of stressors likely contributing to rapid loss of related pollinator species throughout the globe. Scaled-up, international species-monitoring schemes and improved integration of data from formal surveys and community science will substantively improve the understanding of stressors and bumble bee population trends.

Land cover and climate drive shifts in Bombus assemblage composition

Pollinators play pivotal roles in maintaining agricultural and natural plant communities, yet some bee populations are declining. Loss of pollinator habitats as a result of agricultural intensification and urbanization have reduced bee abundance and diversity. Additionally, climate change has affected bee distributions and led to disruption of plant-pollinator synchrony, impacting ecosystem processes. However, how these factors concurrently influence bee assemblages is poorly understood. Therefore, we evaluated bumble bee (Bombus) assemblages in relation to the proportion of agricultural, semi-natural, and urban land cover and interannual variation in temperature, precipitation, and relative humidity in Utah agroecosystems using Bombus captured as bycatch in pest monitoring traps from 2014 to 2018. Bombus assemblage composition was highest in agricultural sites with increased agricultural land cover in the surrounding area, low temperatures, and high relative humidity during the growing season; and lowest in sites with increased urban land cover, high temperatures, and low relative humidity. Functional dispersion did not differ among these groups indicating a range of tongue lengths, body sizes, hair lengths, and hair types were present within all agricultural sites. Further, high beta-diversity, as indicated by unique Bombus assemblages among sites, suggests that all agricultural sites in this study have potential conservation value for maintaining Bombus communities. Therefore, it is important that diverse habitats for pollinators are maintained through targeted management techniques. Additionally, our collection of Bombus from mid-May to mid-September identified phenological overlap within Bombus assemblages, which helps ensure pollination services are provided even if a particular species is lost due to environmental disturbances. However, while there is overlap in functional traits and phenology, considerations should be given due to widespread pollinator declines. Overall, evaluating landscape and climate variables together may yield more realistic results and better inform effective management and land-use planning strategies to prevent ecological homogenization and to foster future resiliency of Bombus populations.

Environmental differences explain subtle yet detectable genetic structure in a widespread pollinator

BackgroundThe environment is a strong driver of genetic structure in many natural populations, yet often neglected in population genetic studies. This may be a particular problem in vagile species, where subtle structure cannot be explained by limitations to dispersal. Consequently, these species might falsely be considered quasi-panmictic and hence potentially mismanaged. A species this might apply to, is the buff-tailed bumble bee (Bombus terrestris), an economically important and widespread pollinator, which is considered to be quasi-panmictic at mainland continental scales. Here we aimed to (i) quantify genetic structure in 21+ populations of the buff-tailed bumble bee, sampled throughout two Eastern European countries, and (ii) analyse the degree to which structure is explained by environmental differences, habitat permeability and geographic distance. Using 12 microsatellite loci, we characterised populations of this species with Fst analyses, complemented by discriminant analysis of principal components and Bayesian clustering approaches. We then applied generalized dissimilarity modelling to simultaneously assess the informativeness of geographic distance, habitat permeability and environmental differences among populations in explaining divergence.ResultsGenetic structure of the buff-tailed bumble bee quantified by means of Fst was subtle and not detected by Bayesian clustering. Discriminant analysis of principal components suggested insignificant but still noticeable structure that slightly exceeded estimates obtained through Fst analyses. As expected, geographic distance and habitat permeability were not informative in explaining the spatial pattern of genetic divergence. Yet, environmental variables related to temperature, vegetation and topography were highly informative, explaining between 33 and 39% of the genetic variation observed.ConclusionsIn contrast to previous studies reporting quasi-panmixia in continental populations of this species, we demonstrated the presence of subtle population structure related to environmental heterogeneity. Environmental data proved to be highly useful in unravelling the drivers of genetic structure in this vagile and opportunistic species. We highlight the potential of including these data to obtain a better understanding of population structure and the processes driving it in species considered to be quasi-panmictic.

Quantifying nectar production by flowering plants in urban and rural landscapes

Abstract Floral resources (nectar and pollen) provide food for insect pollinators but have declined in the countryside due to land use change. Given widespread pollinator loss, it is important that we quantify their food supply to help develop conservation actions. While nectar resources have been measured in rural landscapes, equivalent data are lacking for urban areas, an important knowledge gap as towns and cities often host diverse pollinator populations. We quantified the nectar supply of urban areas, farmland and nature reserves in the UK by combining floral abundance and nectar sugar production data for 536 flowering plant taxa, allowing us to compare landscape types and assess the spatial distribution of nectar sugar among land uses within cities. The magnitude of nectar sugar production did not differ significantly among the three landscapes. In urban areas the nectar supply was more diverse in origin and predominantly delivered by non‐native flowering plants. Within cities, urban land uses varied greatly in nectar sugar production. Gardens provided the most nectar sugar per unit area and 85% of all nectar at a city scale, while gardens and allotments produced the most diverse supplies of nectar sugar. Floral abundance, commonly used as a proxy for pollinators’ food supply, correlated strongly with nectar resources, but left a substantial proportion of the variation in nectar supply unexplained. Synthesis. We show that urban areas are hotspots of floral resource diversity rather than quantity and their nectar supply is underpinned by the contribution of residential gardens. Individual gardeners have an important role to play in pollinator conservation as ornamental plants, usually non‐native in origin, are a key source of nectar in towns and cities.

Biotic and abiotic drivers of plant–pollinator community assembly across wildfire gradients

Abstract Understanding how abiotic disturbance and biotic interactions determine pollinator and flowering‐plant diversity is critically important given global climate change and widespread pollinator declines. To predict responses of pollinators and flowering‐plant communities to changes in wildfire disturbance, a mechanistic understanding of how these two trophic levels respond to wildfire severity is needed. We compared site‐to‐site variation in community composition (β‐diversity), species richness and abundances of pollinators and flowering plants among landscapes with no recent wildfire (unburned), mixed‐severity wildfire and high‐severity wildfire in three sites across the Northern Rockies Ecoregion, USA. We used variation partitioning to assess the relative contributions of wildfire, other abiotic variables (climate, soils and topography) and biotic associations among plant and pollinator composition to community assembly of both trophic levels. Wildfire disturbance generally increased species richness and total abundance, but decreased β‐diversity, of both pollinators and flowering plants. However, reductions in β‐diversity from wildfire appeared to result from increased abundances following fires, resulting in higher local species richness of pollinators and flowers in burned than unburned landscapes. After accounting for differences in abundance, standardized effect sizes of β‐diversity were higher in burned than unburned landscapes, suggesting that wildfire enhances non‐random assortment of pollinator and flowering‐plant species among local communities. Wildfire disturbance mediated the relative importance of mutualistic associations to β‐diversity of pollinators and flowering plants. The influence of pollinator β‐diversity on flowering‐plant β‐diversity increased with wildfire severity, whereas the influence of flowering‐plant β‐diversity on pollinator β‐diversity was greater in mixed‐severity than high‐severity wildfire or unburned landscapes. Moreover, biotic associations among pollinator and plant species explained substantial variation in β‐diversity of both trophic levels beyond what could be explained by wildfire and all other abiotic and spatial factors combined. Synthesis. Wildfire disturbance and plant–pollinator interactions both strongly influenced the assembly of pollinator and flowering‐plant communities at local and regional scales. However, biotic interactions were generally more important drivers of community assembly in disturbed than undisturbed landscapes. As wildfire regimes continue to change globally, predicting its effects on biodiversity will require a deeper understanding of the ecological processes that mediate biotic interactions among linked trophic levels.

Pollinator Communities of Restored Sandhills: a Comparison of Insect Visitation Rates to Generalist and Specialist Flowering Plants in Sandhill Ecosystems of Central Florida

Globally, urbanization and other forms of land use change have been implicated in widespread pollinator declines and disruptions to plant–pollinator interactions. A growing body of literature, however, suggests that urban habitat fragments can provide oases for both plant and insect diversity. A micro-ecosystem on our college campus was created to represent the longleaf pine savannas (sandhills) that once dominated upland ridges throughout the Southeast. To assess the ability of this site to support wild insect pollinators, from May through August for three years (2016–2018) we compared visitation to two abundant flowering plant species, Bidens alba (a generalist-pollinated composite) and Chamaecrista fasciculata (a specialist-pollinated legume), between the campus micro-ecosystem and a nearby site within a large conservation area containing sandhill habitat undergoing restoration. We found that, for both plant species, total insect visitation rates did not differ between years or sites, suggesting that the small urban fragment is capable of maintaining abundant pollinators. The identity of generalist visitors to Bidens alba, however, differed dramatically between sites. Wild hymenopterans constituted more than two-thirds of all insect visits in the campus site but less than half in the conservation area, where butterflies, flies, and beetles were also common visitors. The high density of flowers in the campus site is likely at least partially responsible for the high abundance of hymenopterans, a result consistent with that of many other studies showing that hymenopterans are less sensitive to urbanization than are other insect groups.

First mitochondrial genomes of five hoverfly species of the genus Eristalinus (Diptera: Syrphidae).

The hoverfly genus Eristalinus (Diptera, Syrphidae) contains many widespread pollinators. The majority of the species of Eristalinus occur in the Afrotropics and their molecular systematics still needs to be investigated. This study presents the first complete and annotated mitochondrial genomes for five species of Eristalinus. They were obtained by high-throughput sequencing of total genomic DNA. The total length of the mitogenomes varied between 15 757 and 16 245 base pairs. Gene composition, positions, and orientation were shared across species, and were identical to those observed for other Diptera. Phylogenetic analyses (maximum likelihood and Bayesian inference) based on the 13 protein coding and both rRNA genes suggested that the subgenus Eristalinus was paraphyletic with respect to the subgenus Eristalodes. An analysis of the phylogenetic informativeness of all protein coding and rRNA genes suggested that NADH dehydrogenase subunit 5 (nad5), cytochrome c oxidase subunit 1, nad4, nad2, cytochrome b, and 16S rRNA genes are the most promising mitochondrial molecular markers to result in supported phylogenetic hypotheses of the genus. In addition to the five complete mitogenomes currently available for hoverflies, the five mitogenomes published here will be useful for broader molecular phylogenetic analyses among hoverflies.

Taxonomic and functional trait diversity of wild bees in different urban settings.

Urbanization is one of the major anthropogenic processes contributing to local habitat loss and extirpation of numerous species, including wild bees, the most widespread pollinators. Little is known about the mechanisms through which urbanization impacts wild bee communities, or the types of urban green spaces that best promote their conservation in cities. The main objective of this study was to describe and compare wild bee community diversity, structure, and dynamics in two Canadian cities, Montreal and Quebec City. A second objective was to compare functional trait diversity among three habitat types (cemeteries, community gardens and urban parks) within each city. Bees were collected using pan traps and netting on the same 46 sites, multiple times, over the active season in 2012 and 2013. A total of 32,237 specimens were identified, representing 200 species and 6 families, including two new continental records, Hylaeus communis Nylander (1852) and Anthidium florentinum (Fabricius, 1775). Despite high community evenness, we found significant abundance of diverse species, including exotic ones. Spatio-temporal analysis showed higher stability in the most urbanized city (Montreal) but low nestedness of species assemblages among the three urban habitats in both cities. Our study demonstrates that cities are home to diverse communities of wild bees, but in turn affect bee community structure and dynamics. We also found that community gardens harbour high levels of functional trait diversity. Urban agriculture therefore contributes substantially to the provision of functionally diverse bee communities and possibly to urban pollination services.

Floral integration and pollinator diversity in the generalized plant-pollinator system of Alstroemeria ligtu (Alstroemeriaceae)

Floral integration may result from the combined effects of pollinator-mediated selection, genetic correlations and abiotic factors. Thus, by sampling a set of populations in the field and examining their variation of floral correlations in relation to pollinators and abiotic factors, we intended to shed light on the ecological factors underlying the evolution of floral integration. In this study, floral integration patterns and the composition of pollinator assemblage were characterized across ten populations of Alstroemeria ligtu to test the following: (1) Whether the patterns of floral integration estimated at population level covary with the composition of local pollinator assemblage, climate and/or geographic distance. (2) Whether the magnitude of floral integration decreases with the number or the morphological variability of pollinators. (3) Whether the behavior of the three most widespread pollinators is affected by floral integration. Our results indicated that populations with similar patterns of integration showed greater similitude in pollinator assemblages, but that this was not related to climate or geographic distance. We also found that the most widespread pollinator, Centris nigerrima, invested lower handling time in populations with higher levels of floral integration. The magnitude of floral integration was not related to taxonomical diversity, yet, unexpectedly, correlated positively with the variability of pollinator proboscis length. We suggest that variation in the magnitude and pattern of floral integration across the species range was related to the composition of pollinator assemblage, and not to pollinator diversity per se, nor to climatic variables. A. ligtu was visited by numerous pollinators, but floral integration patterns are likely shaped by only a subset of them, such as C. nigerrima, which is sensitive to variations in floral architecture.

Does Cry1Ac Bt-toxin impair development of worker larvae of Africanized honey bee?

The western honey bee (Apis mellifera L.) is a widespread pollinator species. The present study aimed to test if Africanized honey bee larvae are negatively affected by the ingestion of diet contaminated with the Bacillus thunringiensis toxin Cry1Ac, which is expressed in GM cotton plants. The toxin activity was confirmed in bioassays with the velvetbean caterpillar (Anticarsia gemmatalis), a soybean pest species susceptible to Cry1Ac. The honey bee larvae were subjected to ingestion of either pure larval diet (control), diluted larval diet (diluted control) or larval diet diluted in a Cry1Ac solution at a concentration compatible with the maximum possible field exposure. Although diluted diet slightly increased larval mortality, Cry1Ac ingestion did not affect survival, developmental time, and neither adult body mass nor size, indicating that GM plants are unlikely to significantly impair the development of honey bee larvae. The larval-rearing system reported here was suitable to assess the lethal and sub-lethal effects of GM expressed toxins against honey bee larvae.

Patterns of Speciation in the Yucca Moths: Parallel Species Radiations within the Tegeticula yuccasella Species Complex

The interaction between yuccas and yucca moths has been central to understanding the origin and loss of obligate mutualism and mutualism reversal. Previous systematic research using mtDNA sequence data and characters associated with genitalic morphology revealed that a widespread pollinator species in the genus Tegeticula was in fact a complex of pollinator species that differed in host use and the placement of eggs into yucca flowers. Within this mutualistic clade two nonpollinating "cheater" species evolved. Cheaters feed on yucca seeds but lack the tentacular mouthparts necessary for yucca pollination. Previous work suggested that the species complex formed via a rapid radiation within the last several million years. In this study, we use an expanded mtDNA sequence data set and AFLP markers to examine the phylogenetic relationships among this rapidly diverging clade of moths and compare these relationships to patterns in genitalic morphology. Topologies obtained from analyses of the mtDNA and AFLP data differed significantly. Both data sets, however, corroborated the hypothesis of a rapid species radiation and suggested that there were likely two independent species radiations. Morphological analyses based on oviposition habit produced species groupings more similar to the AFLP topology than the mtDNA topology and suggested the two radiations coincided with differences in oviposition habit. The evolution of cheating was reaffirmed to have evolved twice and the closest pollinating relative for one cheater species was identified by both mtDNA and AFLP markers. For the other cheater species, however, the closest pollinating relative remains ambiguous, and mtDNA, AFLP, and morphological data suggest this cheater species may be diverged based on host use. Much of the divergence in the species complex can be explained by geographic isolation associated with the evolution of two oviposition habits.