"Many insects provide valuable ecosystem services, including those that support our food supply. Beneficial insects such as pollinators fulfill part of this role by contributing to approximately one third of the global food crop production. Over the past few decades, pollinators have faced declining populations due to a variety of factors such as agricultural intensification, lack of floral and nesting resources, and disease. One method used in agricultural settings to help sustain pollinator populations is designating unfarmed habitat such as ditches and field margins for habitat enhancement in the form of hedgerows and wildflower strips. These floristically rich areas can be tailored to bloom both before and after crop bloom to help sustain pollinators during the time when crops are not in bloom. In turn, bee populations can benefit from the consistent availability of resources in these areas of habitat enhancement. This dissertation explores how habitat enhancement affects nesting density of a common wild pollinator, Bombus impatiens. Further, this research also aims to determine how foraging preferences change and how bumble bee disease transmission and prevalence respond to habitat enhancement. Research was conducted at 15 commercial highbush blueberry (Vaccinium corymbosum) fields in southwest Michigan containing either no restoration, a newly planted restoration, or a mature (5-8 year old) restoration in the field margin from 2015 to 2017. I found that sites with new and mature restorations significantly boosted B. impatiens population abundance in the surrounding landscape. Sites with new restorations also had significant increases in B. impatiens colonies within one year of establishment and a tripling in density over the course of the three-year study. In my second study, at sites without restorations bumble bees foraged on a variety of flowers, whereas in sites with new and mature restorations, greater numbers of highly attractive flowers allowed bumble bees to retain floral constancy. Further, this study reveals the sensitivity of plant-pollinator networks to variation in habitat management in similar environments, highlighting the need for greater replication in studies that monitor changes in plant-pollinator networks over time. Finally, I found that the prevalence of Crithidia bombi, a common pathogen of bumble bees, in bumble bee gut tissue and on flower surfaces is significantly increased at sites with habitat enhancement. Flowers that were considered highly attractive were more likely to screen positive for a pathogen, highlighting the important role that flowers play in the horizontal transmission of pathogens. The results of this work shed new light on the underlying complexity of bee restoration in agricultural settings and will help inform best management practices for bee conservation in the future."--Pages ii-iii.
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