Biology subjects

Sponsler, D. B.

Publications and source records attributed to Sponsler, D. B..

3 recordsLinked to original sources

bioRxiv2019

Characterizing the floral resources of a North American metropolis using a honey bee foraging assay

Roughly a third of described insect species visit flowers, making the flower-insect interface one of the chief pillars of global biodiversity. Studying flower-insect relationships at the scale of communities and landscapes has been hindered, however, by the methodological challenges of quantifying landscape-scale floral resources. This challenge is especially acute in urban landscapes, where traditional floral surveying techniques are ill-suited to the unique constraints of built environments. To surmount these challenges, we devised a \"honey bee foraging assay\" approach to floral resource surveying, wherein continuous colony weight tracking and DNA metabarcoding of pollen samples are used to capture both the overall availability and taxonomic composition of floral resources. We deploy this methodology in the complex urban ecosystem of Philadelphia, PA, U.S. Our results reveal distinct seasonality of floral resource availability, with pulses of high availability in May, June, and September, and a period of prolonged scarcity in August. Pollen genus richness mirrored this pattern, with peak richness in May and June. The taxonomic composition of pollen samples varied seasonally, reflecting underlying floral phenology, with especially strong turnover between May and June samples and between August and September samples delineating well-defined spring, summer, and fall floral resource communities. Trait analysis also revealed marked seasonal structure, with spring samples characterized by trees and shrubs, summer samples including a stronger presence of herbaceous \"weeds\", and fall samples dominated by woody vines. Native flora predominated in spring, giving way to a preponderance of exotic flora in summer and fall. Our study provides a detailed portrait of floral resources in a complex urban environment. At a basic level, this yields insight into the assembly of novel urban floral resource communities, showcasing, for example, the emergence of a woody-vine-dominated fall flora. At an applied level, our data can inform urban land management, such as the design of ecologically functional ornamental plantings, while also providing practical guidance to beekeepers seeking to adapt their management activities to floral resource seasonality. Methodologically, our study demonstrates the potential of the honey bee foraging assay as an efficient and standardizable technique for landscape-scale floral resource surveying.

ecology↗

bioRxiv2019

Honey bee pollen foraging ecology across an urbanization gradient

Understanding animal foraging ecology requires large samples sizes spanning broad environmental and temporal gradients. For pollinators, this has been hampered by the laborious nature of morphologically identifying pollen. Metagenetic pollen analysis is a solution to this issue, but the field has struggled with poor quantitative performance. Building upon prior laboratory and bioinformatic methods, we applied quantitative multi-locus metabarcoding to characterize the foraging ecology of honey bee colonies situated along an urban-agricultural gradient in central Ohio, USA. In cross-validating a subset of our metabarcoding results using microscopic palynology, we find strong concordance between the molecular and microscopic methods. Our results show that, relative to the agricultural environment, urban and suburban environments were associated with higher taxonomic diversity and temporal turnover of honey bee pollen forage. This is likely reflective of the fine-grain heterogeneity and high beta diversity of urban floral landscapes at the scale of honey bee foraging. Our work also demonstrates the power of honey bees as environmental samplers of floral community composition at large spatial scales, aiding in the distinction of taxa characteristically associated with urban or agricultural land use from those distributed ubiquitously across our landscape gradient.

ecology↗

bioRxiv2019

Rising insecticide potency outweighs falling application rate to make US farmland increasingly hazardous to insects

Each year, millions of kilograms of insecticides are applied to crops in the US. While insecticide use supports food, fuel, and fiber production, it can also threaten non-target organisms, a concern underscored by mounting evidence of widespread insect decline. Nevertheless, answers to basic questions about the spatiotemporal patterns of insecticide use remain elusive, due in part to the inherent complexity of insecticide use, and exacerbated by the dispersed nature of the relevant data, divided between several government repositories. Here, we integrate these public datasets to generate county-level annual estimates of total insect toxic load (honey bee lethal doses) for insecticides applied in the US between 1997-2012, calculated separately for oral and contact toxicity. To explore the underlying drivers of the observed changes, we divide insect toxic load into the components of extent (area treated) and intensity (application rate x potency). We show that while contact-based insect toxic load remained relatively steady over the period of our analysis, oral-based insect toxic load increased roughly 9-fold, with reductions in application rate outweighed by disproportionate increases in potency (toxicity/kg) and increases in extent. This pattern varied markedly by region, with the greatest increases seen in Heartland and Northern Great Plains regions, likely driven by use of neonicotinoid seed treatments in corn and soybean. In this \"potency paradox,\" US farmland has become more hazardous to insects despite lower volumes of insecticides applied, raising serious concerns about insect conservation and highlighting the importance of integrative approaches to pesticide use monitoring.\n\nSignificance statementPrevious analyses disagree about whether US insecticide use is increasing or decreasing, a question of significant importance given the putative role of insecticides in recent insect declines. We integrated information from multiple national databases to estimate insect toxic load (represented as honey bee lethal doses) of the agricultural insecticides applied in each US county from 1997 to 2012, and factors responsible for its change. Across the US, insect toxic load - calculated on the basis of oral toxicity - increased 9-fold. This increase was due to increases in the potency (toxicity/kg) of insecticides applied and in the area treated; the volume of insecticides applied declined. Toxic load increased most dramatically in regions where neonicotinoid seed treatments for field crops are commonly used.

ecology↗