Native Bee Nesting Abundance and Diversity at the Lillian Anderson Arboretum
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Wild bees play a crucial role as primary pollinators of flowering plants in the United States and around the world. In the last few decades bee numbers have been declining rapidly due to the increased use of pesticides, habitat loss and fragmentation, pollution, pathogens, parasitism and climate change. This has been documented in Michigan with the decline in many bee species across the state and the recent extirpation of a species of bumble bee (Bombus affinis) from the state. Bees require resources such as food, protection from pesticides, and nesting resources in order to thrive. Kalamazoo College recently obtained the rights to improve and maintain the strip of powerline that runs through the college's Lillian Anderson Arboretum. The Pollinator Enhancement Project is scheduled to take place in the spring and summer of 2020 and will include the removal of invasive plants, planting of native forage plants, and provision of nesting habitat for wild bees on the powerline. The purpose of this study was to catalog the diversity and abundance of bee genera along the powerline, and assess the diversity and abundance of bees utilizing above ground nesting resources we provided in the form of artificial stem and cavity nests. To accomplish this, bees were sampled throughout the summer of 2019 using two different types of traps (blue vane traps and bee bowls) and nesting bees were studied using three types of artificial stem nests (drilled blocks, large PVC, and small PVC nests) and one nest type of cavity nest for social bees (bumble bee box). Nests were monitored for occupancy over the course of the summer. A total of 786 bees belonging to 21 genera were captured at the powerline representing 48% of genera diversity of bees found in Michigan and 60% of the diversity found in Kalamazoo county. We found that the drilled block nest design was significantly more attractive to native stem nesting bees compared to large PVC nests (p=0.0002), and more bees occupied 6 mm tubes than 8 mm or 4 mm. There was also a significant difference when considering both nest type and tube size as indicated by a two-way ANOVA test (f=3.34; p=0.043). Using small PVC nests, we determined that the orientation of stem nests did not significantly affect occupancy rate (p=0.287). X-ray imaging revealed that artificial stem nest tubes were occupied predominantly by bees and wasps, with size of tube being a significant predictor of occupant type. No bumble bees colonized the cavity nests we provided. This study utilized proven techniques to provide insight into bee diversity and abundance at the Lillian Anderson Arboretum and compared the effectiveness of several different artificial stem nest designs. The results of this study provides information valuable to improving both local habitats and international approaches to studying stem nesting bees.