Center Update: Pollinator Communities in Turfgrass Systems
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Research and Outreach to Support Pollinators in North Carolina: A Comparison of Pollinator Communities in Managed Turfgrass Systems in the Piedmont and Sandhills of North Carolina
PIs: Terri Billeisen and Danesha Seth Carley
Insect pollination of flowering plants provides an important ecosystem service and is essential for field, fruit and horticultural crop production (Free, 1993). Pollination not only helps promote a diverse plant community in commercial production but can also improve aesthetics in the urban landscape by encouraging growth in native flowering plant stands. As worldwide urbanization continues to increase, transformations in the current landscape have led to decreased habitat and food supply for insect pollinators such as bees, wasps, butterflies, moths, flies and beetles. One way to offset habitat loss is to incorporate native wildflower plantings in or adjacent to currently managed green spaces in urban environments. Even in small spaces, wildflower presence has been shown to increase insect pollinator abundance and diversity (Blackmore and Goulson, 2014). The objectives of this study were to examine pollinator communities initially in established turfgrass systems, establish pollinator-friendly habitat at these sites and observe how these communities changed in abundance and diversity post-establishment.
Five managed green spaces (golf courses and home lawns) were selected based on location, site suitability for establishment and management intensity in the summer of 2018. Each site was walked at a moderate pace for 20 minutes using a modified sweep or zip net to collect flying insects. An aerial net and kill jars were used to collect butterflies and to protect specimens. In each sample location, three transects 15 m long were established 1.5 m apart. Blue, white, and yellow pan traps were placed along each transect for a total of 15 pan traps (5 blue, 5 white, and 5 yellow) per sampling location. Pan traps were filled with unscented soapy water and collected after 5 hours between 8:15 and 16:45. Ambient temperature and general weather conditions were recorded at the beginning and end of sampling periods. Sampling did not occur on cool (below 60 degrees F) or overcast days. Sites were sampled once each month for insect pollinators from Jun 1 to Oct 9 to get a baseline for pollinator activity prior to habitat establishment. Insects collected from sweep netting were stored in a freezer until specimens were washed and pinned. Insects collected from pan traps remained in Whirl-Paks with ethyl alcohol (95% denatured with methyl and IPA; Fisher Science Education) until washed and pinned, but were not stored for more than 24 hours prior to washing. Specimens will be identified as follows: bees and butterflies to species, flies categorized as syrphid (flower flies) and non-syrphid groups.
Insect abundance and richness was analyzed using PROC MIXED of the Statistical Analysis System. Insect sampling frequency was increased from once a month in 2018 to once every two weeks in 2019. To account for this, insect count data was pooled into three main sampling periods: early to mid-summer, late summer/early fall and mid-fall. Bee species richness and evenness was determined using the Shannon-Weiner index to give us an indication of relative biodiversity. The Shannon-Weiner measure H’ value indicates the diversity by incorporating both species richness and relative species abundance within a site. H’ will increase with the number of bee species found and their equitability. Equitability assumes a value between 0 and 1, with 1 representing complete evenness (all equal).
Results and Discussion
Insect pollinator abundance increased substantially from 2018 (129 total specimens; 63 bees, 15 syrphid flies, 51 lepdiopterans) to 2019 (675 total specimens; 395 bees, 124 syrphid flies, 156 lepidopterans). This increase is likely due in part to the increased number of samples taken in 2019 but can also be attributed to the establishment of wildflower areas providing additional food sources and refuge in managed green spaces. This finding echoes those of previous studies that indicated increased floral diversity increases both abundance and diversity in pollinator communities, however, site selection (golf course vs home lawn) was also significant in terms of insect abundance. Some significance could be attributed to size differential of wildflower areas in home lawns (4.71 m²- 9.29 m²) compared to golf courses (9.29 m²-1,484.77 m²). However, the home lawn with the smallest wildflower coverage (HL2), had the largest abundance of bees collected (112 spp.) in 2019 and was also one of the most diverse sites with 21 different species represented (Table 1). While golf course GCH6 had the largest wildflower area (1,484.77 m²) and also had 21 different bee species, only 88 total bee specimens were collected. Likely these differences could be attributed to the landscape surrounding the study sites. A typical 18-hole golf course is 150 acres with managed turfgrass covering 67% of the total acreage, and only 16% of dedicated landscapes not containing turfgrass (Lyman et. al., 2007). Because home lawns are situated in residential neighborhoods that are often landscaped with an assemblage of plant material, they have the potential to appeal to broader pollinator communities than a homogeneous landscape.
Wildflower establishment and site selection were both significant in terms of insect diversity. Twenty four species of bees collected in 2019 were not found in 2018: Bombus griseocollis, Epeolus lectoides, Holcopasites calliopsidis, Melissodes comtoides, Melitoma taurea, Eucera pruinosa, Ptilothrix bombiformis, Svastra obliqua, Svastra petulca, Xylocopa virginica, Agapostemon splendens, Augochlora pura, Lasioglossum cockerelli, Lasioglossum coreopsis, Lasioglossum floridanum, Lasioglossum hitchensi, Lasioglossum illinoense, Lasioglossum zephyrus, Megachile exills, Megachile mendica, Megachile petulains, Megachile roturdata, Megachile texana, and Stelis lateralis. Apis mellifera L., the honey bee, was only represented by a total of four specimens collected both years and was the only bee species collected not native to North Carolina. In 2018, GCH6 was the most diverse site, containing 10 different species of bees with the highest H’ value of 2.11 and equitability value of 0.92 (Table 1). In contrast, GHC5 had the lowest H’ value of 0.69, yet was completely even with an equitability value of 1,meaning there were equal numbers of each species present. In 2019, the most diverse sites were HL2 and GCH6, having 21 species of bee present. HL2 had an H’ value of 2.36 and equitability value of 0.74. GCH6 had both a higher H’ value of 2.55 and equitability value of 0.81.
Results from this study confirm that pollinator refuge establishment in managed green spaces increase both abundance and diversity of insect pollinators. Native pollinator species locations and ID tips from this work are currently being assembled for publication as a complete field guide as part of an outreach component to this research.
Table 1. Results for the 2018 and 2019 Shannon-Wiener Diversity Index for each site, number of species, total number of bees collected, Shannon-Wiener calculation (H’), and equitability.
|Site||Species #||Total bees||H’||Equitability||Species #||Total bees||H’||Equitability|
Blackmore, L.M. and Goulson, D., 2014. Evaluating the effectiveness of wildflower seed mixes for boosting floral diversity and bumblebee and hoverfly abundance in urban areas. Insect Conservation and Diversity, 7(5), pp.480-484.
Free J.B. 1993. Insect pollination of crops. Academic Press, London.
Lyman, G.T., Throssell, C.S., Johnson, M.E., Stacey, G.A. and Brown, C.D., 2007. Golf course profile describes turfgrass, landscape, and environmental stewardship features. Applied turfgrass science, 4(1), pp.0-0.