Date on Senior Honors Thesis
Senior Honors Thesis
University of Louisville
College of Arts and Sciences
Ecology; urban ecology; insects; urban insects
Insect populations, especially those of pollinators, have been steadily declining across the globe in recent decades, a trend that is intensified in cities. Since the conservation of pollinators is crucial for maintaining ecosystems and ecological processes, new approaches are being promoted beyond those of conserving large natural areas. Urban native plant gardens could potentially offset some of these losses locally. This research attempts to set a local baseline for the insect diversity in urban gardens in Louisville and determine whether differences exist in garden insects in cities versus suburbs in Jefferson County, Kentucky. To address the land-use question we established 23 collection sites across the county ranging in degree of “urbanness”, with four being established in local parks to serve as natural reference sites. We also addressed a methodological question concerning the abundance and types of insects caught using different colored bowls set at two different heights. Each collection site consisted of 6 bowls filled with detergent-water. Three were 100-cm above the ground and three were 15-cm above the ground. At each height we set up a blue, white and yellow bowl filled with detergent-water to capture insects. We collected insects caught over a 24-hour period at the end of June and again at the end of July in 2017. Identification was performed to taxonomic order, with additional subcategories below order for certain groupings. The impact of bowl color, bowl height, time period of capture, and degree of “urbanness” (measured by % Impervious Surface) on abundance and diversity of insects captured were assessed. We found little difference in insect abundance at the taxonomic order level among the native plant gardens and between gardens and the meadow reference sites. However, we did find evidence in July that bee abundance was lower in urban vs. suburban and meadow locations. We also found that yellow bowls captured the most insects, while height also played a significant role, with the high bowls capturing more than low bowls. More insects were captured in July than June. Our findings suggest that the creation of more native plant gardens in cities and suburbs may well be a viable conservation strategy for supporting insects, including pollinators.
Lawson, Jacob T., "Insect populations across an urban-to-suburban land use gradient." (2019). College of Arts & Sciences Senior Honors Theses. Paper 189.
Retrieved from https://ir.library.louisville.edu/honors/189
Over the past few decades, insect populations have been steadily decreasing, with such trends being worse in cities. This is grounds for alarm as insects are vitally important for their numerous biological roles in food webs and as pollinators. To stop these declining populations, native plant gardens may help provide shelter, reproductive habitat, and food for these insects. This research seeks to determine the impact of these gardens along the level of “urbanness” of a city, ranging from urban to suburban. Gardens were selected across Jefferson County and bowls of three colors and two heights were used to capture insects. These insects were then counted and identified to Taxonomic Order and some (bees, chalcid wasps) to the Family level. Overall, there was no clear relationship between the degree of urbanness surrounding gardens and the number of insects collected and their relative proportions at the Order level. However, our data suggest that bee abundance may be lower in the most urban gardens. We did find that more insects were captured in July as compared to June and that the color and height of placement of bowls used to capture insects differed, with yellow bowls placed 1-meter above the ground capturing the most insects. We conclude from this initial study that native plant gardens may be useful in supporting insects, including pollinators, in cities such as Louisville, Kentucky.