Bumble bees provide vital pollination services in both native and agricultural landscapes. However, in recent years, bumble bee populations have experienced global population declines. The primary causes of these declines have been attributed to the environmental impacts of pathogens, pesticide use and habitat fragmentation. While research has examined the impacts of pathogens, there is limited information on the effects of pesticides and habitat fragmentation on native bumble bees. Hence, the objectives of my dissertation research were to: 1) assess the toxicological impacts of pesticides used in two important bee-pollinated crops on queens and workers; 2) determine the impacts of forage resource availability on bumble bee colonies; 3) examine pollen foraging behavior of bumble bees in a late season mass-flowering agricultural landscape; and 4) document observations on trends towards bivoltinism in three western North American bumble bees. This research was conducted in the lab using wild and lab reared colonies, and in an agricultural landscape in the Willamette Valley of Western Oregon. In pesticide bioassays the impacts of residual toxicity of five classes of pesticides used in highbush blueberry and red clover cropping systems, were tested on queen and worker bumble bees, respectively. The results indicated variation in responses to the same insecticide by queens and workers, and to the same class of compounds by workers. Also, toxic effects were documented for both queens and workers to pesticides considered to be "safe" for bees. The impacts of forage resource availability were evaluated by exposing bumble bee colonies to four quantities of pollen, four quantities of nectar and three feeding frequencies of pollen. The study documented an inverse relationship between larvae and workers to resource type and availability. In addition, the type of larval mortality displayed by colonies, larval ejection or within clump mortality, was dependent on worker mortality. The individual and colony-level pollen foraging behavior of bumble bees was examined by placing colonies in red clover. Observations in the field on forager abundance, and at the colony-level on the duration and number of pollen trips and weight of stored pollen documented that red clover is an important resource for bumble bees. Pollen analysis revealed that in addition to red clover, Himalayan blackberry was also a key forage resource for bumble bees. Red clover resources at the end of the season may also benefit bumble bees by allowing for the creation of a second generation. Observations on both field and lab-reared queens document a trend towards bivoltinism in three species of western North American bumble bees. Agricultural habitats are vital for sustaining bumble bee populations. However, given the potential for pesticide impacts and temporal availability of flowering plants, these landscapes must be managed to provide maximum benefit to bumble bees. Results from this research should assist growers and researchers in developing landscape management and production practices geared toward the conservation and enhancement of native Bombus spp. populations in western Oregon. / Graduation date: 2011