Final report for GS18-186
The research was conducted at the research farm of the USDA-ARS Dale Bumpers Small Farms Research Center in Booneville, AR, where research sites with different seed-mixes were established. Six, 0.40-acre conventional plots were used for the study. Out of six plots, three plots were planted with mixture of native flowering plants and remaining three were planted with native warm season grasses. The main objective of this study was to examine the impact of grazing on seed mixes of native forb/legume/grass (FLG; www.hamiltonnativeoutpost.com) and warm season grasses (WSG; equal seed mix of equal mix of Andropogon gerardi, Tripsacum dactyloides, and Sorghastrum nutans) on bees and other non-bee insects in livestock pasture in Southeastern USA. Each pasture was divided into two halves (in a split-plot design) using an electric fence in which one plot was grazed and the other plot was non-grazed. Blue vane traps and a pair of yellow and blue pan traps were used for sampling bees and other insects. Plant species composition in two types of seed mixes (FLG and WSG) was also recorded. The abundance, diversity, and evenness of bee communities and other insects were greater in non-grazed plots as compared to grazed plots. However, species richness, as measured by rates of species accumulation relative to sampling effort, was not different among treatments. Establishment of pastures using seed mixes of native forb/legume/grass and warm season grasses, respectively, was variable, with undesirable species often exceeding 50% of the plant community in both pasture types. Results show that a diverse array of bees and other insects may be found in livestock pasture systems, but that reduction in bee and insect diversity in grazed areas highlight the importance of rotational grazing regimes to allow for sufficient floral resources for pollinators at relevant scales.
- To examine impacts of grazing native forb and grasses on insect pollinators and beneficial arthropod community in pasture system.
- To determine to impact of native floral enhancement on insect pollinators and beneficial arthropods in pasture ecosystems
This study was conducted during the summer of 2018 and 2019 at the USDA-ARS Dale Bumpers Small Farms Research Center in Booneville, Arkansas (35.09 °N, 93.95 °W). Conventionally managed plots (n =6 each of 0.4 ha size) established as a livestock pasture were used for the study. Prior to establishment of pasture, the field was sprayed with herbicides, viz: Roundup® (41% glyphosate, 4.67 l ha-1) in June, July, September, and October of 2016 and January of 2017, and with Outrider (Monsanto, St. Louis, MO; 0.096 l ha-1) on September 2016 using a Continental Belton cluster nozzle sprayer (Continental Belton McAlester, SR: A44117, Oklahoma City, OK). Each plot was further divided into two halves (0.2 ha each) using electric fence in which half of the plot was grazed by sheep and remaining half was left un-grazed. Sheep (n = 15) were allowed to graze for 4 days per week (Monday through Thursday) and traps for sampling bees were set up on Friday to collect samples on Sunday (after 48 hours). Blue vane traps and pan traps were used to sample visiting insects in each plot to compare abundance and species richness of pollinators and other insects between the grazing management treatments (grazing vs non-grazing). Samples were collected weekly from first week of July to mid-August. Samples were kept in vials containing 70% ethyl alcohol, transported to the lab, air dried, sorted, pinned and later identified up to the species level using dichotomous keys and and online taxonomic resources such as Discover Life (www.discoverlife.org). Species identification were further confirmed by taxonomic expert working with bee species identification. Plant species composition (botanical composition) in grazing and non-grazing plots was surveyed on a weekly basis during June and July months to capture the number and percentage of vegetation cover and floral resources during the sampling period.
A diverse community of bee and non-bee insect communities were found in grazing and non-grazing pastures in Arkansas. During the sampling period both years, we collected a total 1570 bees, including 678 bees in grazed plots and 892 bees in non-grazed plots. Lasioglossum imitatum (21.3%), Melissodes communis (8.7%), Bombus pensylvanicus (13.0%), Ceratina strenua (8.2%), and Augochlorella aurata (6.0%) were the most common bee species, whereas non-bee species belonging to families Dolichopodidae, Buprestidae, Meloidae, Milichiidae, and Mordellidae were the most abundant non-bee insects found in this study. Although capture rates of insects varied among trap types, we still found that bee and non-bee insect communities were generally more abundant and diverse in non-grazed pasture plots relative to grazed plots, even when situated in close proximity to one another. In this study, large number of diverse insect species were present in all the pasture plots irrespective of flowering forbs or native grass possibly due to habitat structure and ability to adapt in these types of ecosystems. Percentage of desirable (seeded forage) and undesirable (not seeded) both were between 40 – 60% and varied between plots in seed mix plot with forb/legume/grass. About 8.6% of the ground was bare (no forage species). Likewise, the percentage of desirable plants in warm season grass plots were as low as 20-30% (Andropogon gerardi, Tripsacum dactyloides, Sorghastrum nutans). Among the three major grass species all three plots majorly contained weeds (around 60-70%). Overall, sheep grazing within the study pasture systems had an effect on insect abundance, diversity, and community assemblages, and differences in such species assemblage patterns may provide insight on how the insect community structure is influenced by grazing practices in pasture systems.
Educational & Outreach Activities
Sharma Acharya. R. 2021. Dissertation. “Establishment of Pollinator Habitat within a Livestock Pasture Ecosystem” was submitted for the partial fulfillment of Doctoral research at University of Arkansas, Fayetteville, AR
Roshani Sharma Acharya, Timothy Leslie, Joan Burke, Kelly Loftin, and Neelendra Joshi. 2021. “Grazing influences the diversity and community composition of bees and other insects in livestock pastures”. Manuscript in preparation for submission.
There is widespread farmers adoption of establishment of pollinator diversity by maintaining native flowers plants and grazing system. Other studies are carried out to find ways to establish bees and non-bee pollinator diversity in livestock pasture. Findings of this study will be helpful to growers and land owners in developing strategies to manage their pasture land to support pollinators and insect biodiversity.