Joshua Botti-Anderson - May 2018

In the public eye, bees are typically seen as faithful servants of humans, producing honey and pollinating crops, their home a carefully managed box in which the population of collaborating workers numbers in the tens of thousands. On the other hand, wasps have gained a largely negative reputation; the very word conjures up images of angry, stinging swarms of yellow-jackets, ready to wreak havoc on the next suburban barbeque. These common perceptions, however, disregard a group of insects that are in fact very beneficial and peaceful towards humans: the solitary bees and wasps. Instead of congregating in colonies and socializing with one another, solitary species act alone; females construct nests independently, collecting nesting materials and food for a handful of their own offspring. An important group of solitary species are known as the cavity-nesters, which construct nests in naturally-occurring narrow channels. Throughout the summer, solitary cavity-nesting bees collect pollen, while cavity-nesting wasps collect insect prey, building a sequence of brood cells up to the opening of a channel, which is then capped with mud or debris. Despite a general lack of public awareness, the benefits provided by these animals have important implications for humans: solitary bees are essential pollinators of both crops and native plants, while solitary wasps prey upon pests. The Montana landscape hosts a wide array native cavity-nesters and, given the benefits they provide, population health within altered landscapes is of special concern. Human activities have created extensive habitat modification in urban areas, and understanding how this affects solitary bees and wasps would be essential to any conservation efforts directed towards these species. While working as a lab assistant, under the enlightening influence of Dr. Casey Delphia and Dr. Kevin O’Neill, I became enamored with the notion of investigating this fascinating topic.

In light of the significance of cavity-nesting solitary bees and wasps, the objective of our project is to assess the diversity and abundance of cavity-nesting wasps and bees, comparing urban environments in Bozeman to adjacent semi-natural and agricultural landscapes. By gaining insights into the species present in urban environments, the beneficial services provided by cavity-nesters can be pinpointed to species that thrive, and the effects of natural enemies and introduced species more readily understood. A useful tool for biodiversity assessments of cavity-nesters are trap-nests, which mimic the natural channels colonized by these species and allow for easy harvesting of capped-off, or completed nests. The trap-nests we are using for this study (which are of the design used by Drs. O’Neill and Delphia in past research) consist of an aggregate of wooden blocks zip-tied together, each drilled with holes that accommodate cardboard tubes of seven different diameters. The cavity-nesters construct their brood cells within these carboard tubes and, when brandishing an end cap, can be harvested and returned to the lab.

In early May, we prepared and pieced together the components of each trap nest. With my immense gratefulness, Dr. O’Neill cut and drilled all the wooden block pieces that were needed or required augmentation. We then patched these up with aluminum tape, treated them with linseed oil, and pieced them together to create 16 trap-nests, each designated for a single field site (eight agriculture/semi-natural, eight urban). The purpose of including seven diameters of nesting tubes is to account for a broad range of cavity-nesting bees and wasps, which differ in body size and nesting strategy.

Trap-nest construction; photos taken by Joshua Botti-Anderson

While many of the agricultural and semi-natural sites could be located on MSU’s research farms (e.g. Post Farm, Lutz Farm, etc.), access to urban sites required us to communicate with homeowners who were willing to host a trap-nest in their yards. As such, a substantial portion of the preparation for this project involved us reaching out to individuals and organizations. Starting in mid-April, we began emailing potential hosts. My mentors’ contacts and friends in the sciences, horticulture, and science-supporting public proved to be a valuable resource, as many individuals responded with great willingness to support our project. As potential trap-nest sites were obtained, we began compiling a list and constructed an aerial map, placing our options in the criteria of urban environments (of which we needed eight locations) and agricultural or semi-natural areas (also eight). Other criteria guiding the selection process were security (from tampering) of the trap-nests, accessibility, adequate distance separation, and the general absence of other confounding variables. Once we had narrowed down our list of 16 locations, we emailed the individuals whose sites we had chosen and inquired about days and times to meet and place trap-nests.

On May 14th, Dr. Casey Delphia and I loaded up the field vehicle and set out from Marsh Labs, on a mission to place at least ten trap-nests. On our list for this day were several of MSU’s research farms, as well as a handful of urban sites, since many of the site hosts had already responded and scheduled times for placement on Monday. Among the supplies we brought were the trap-nests (obviously), metal fence posts (to which the trap-nests are fixed), a post-pounder, a compass, and the cardboard tubes for filling the holes of the trap-nest. When visiting urban locations, Casey and I met with homeowners, who showed us the appropriate places to place trap-nests in their yards. Everyone we visited was curious about the project, and we were happy to answer any questions, which ranged from direct inquiries into the study, to more general questions about the biology of cavity-nesting bees and wasps. In addition, the flow of compliments lifted my spirits and helped me become more attuned with the importance of this project. Before placing the trap-nests, we selected an appropriate spot, which had to be backed by a line of trees or shrubs (for shade from the late afternoon sun), and open to the southeast (for warmth from the early to midday sun). We then pounded a fence post in place, aligned (using the compass) so that once the trap-nest was secured, it was facing southeast. After securing the trap-nest to the fence post with zip-ties, we filled each hole with its corresponding carboard tube size. Monday proved to be hugely successful, as we were able to place out 11 of the 16 trap-nests. Beautiful weather followed us into Tuesday, and we placed three more trap-nests in their locations, leaving just two at the time of writing.

Left: field vehicle with supplies. Right: trap-nest in the Pollinator Garden in Langohr Park; photos taken by Joshua Botti-Anderson

Left: Joshua loading cardboard tubes. Right: Joshua and Dr. Delphia triumphing over the completed trap-nest; photos courtesy of Dr. Casey Delphia

Future work on this project will include placing the remaining trap-nests and weekly monitoring (which will last the entire summer). Traveling from nest-to-nest via bicycle, I will harvest completed carboard tubes, which are characterized by an end cap of mud or plant debris, and replace them with empty ones. An advantage to using removable carboard tubes is that it enables us to sample populations throughout their active season, and ensures continual use of the trap-nests by cavity-nesters. Throughout the summer, I will determine the identity of cavity-nesters by analyzing the composition of the end cap. In addition, the completed nests will be overwintered and reared next spring, which will enable me to conduct genus-level identification. By conducting this project, I hope to gain a deep understanding of the health of populations of cavity-nesting bees and wasps in urban environments, including the overall species composition and abundance, as well the effects of natural enemies. Knowing which species thrive in disturbed conditions, and which landscape factors play a significant role in population health, would be essential to management changes aiming to enhance cavity-nester populations.

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