In cranberry (Vaccinium macrocarpon Aiton) cultivation, farmers typically rent colonies of honey bee (Apis mellifera) for pollination. However, the efficiency of this bee at pollinating cranberries in Oregon, as in other regions, is questionable. Bumble bees (Bombus sp.) are reportedly effective in other regions, but their impact in Oregon is unknown. My objectives were to: (i) Compare bumble bee and honey bee pollination efficiencies under caged conditions; (ii) Estimate the abundance of bumble bees, honey bees, and other pollinators on an Oregon cranberry farm; and iii) Analyze and compare sources of pollen collected by bumble bees and honey bees in Oregon cranberries. In comparing pollination efficiencies of bumble bees and honey bees under caged conditions, the analysis of variance of data from the cage study indicated that bumble bee and honey bee pollinated plants yielded statistically equivalent average numbers of cranberries (1421 ± 302.5 and 1405 ± 347.6 berries/m², respectively) and weight of berries (11.5 ± 2.42 and 11.5 ± 2.77g/m²). However, bumble bees may have increased fruit set in honey bee treatments. On one occasion, bumble bees were found in the honey bee treatment, and may have contributed to the pollination of flowers in these plots. To estimate the abundance of pollinators, visual observations and were blue vane traps were utilized. Thirty-four timed visual observations in transects of cranberry beds were performed over on four dates during cranberry bloom. Blue vane traps were set-up on five occasions during bloom for two day periods. In the visual observations, honey bees (3.5 ± 0.58/min) were observed more frequently than bumble bees (1.2 ± 0.20/min). Bumble bees of four species made up 69.1% of trapped bees while honey bees made up 16.6% of bees caught in blue vane traps. On an Oregon cranberry farm during bloom periods in 2009, 2010 and 2011, pollen was collected from honey bee colonies using pollen traps. In 2010 and 2011, pollen was hand collected from reared bumble bee (B. vosnesenkii) colonies at the same farm. A total of 2937 honey bee pollen loads and 171 bumble bee pollen samples (137 scopal pollen loads, and 34 samples from with the colony) were individually acetolyzed and compared to a reference collection using light microscopy. Each pollen load was homogenized and 100 pollen grains were identified and counted to determine the percentage of each pollen type. Pollen collected by honey bees consisted of 29.1 ± 1.4% (2009), 18.3 ± 2.4% (2010), and 23.0 ± 1.1% (2011) cranberry pollen. Cranberry pollen contributed a higher percentage (56.0 ± 6.1%, and 70.4 ± 4.3% in 2010, and 2011, respectively) in bumble bee collected pollen. Both bee species collected pollen from non-target plants including those in the following families: Asteraceae, Fabaceae, Ranunculaceae, and Roseaceae. Native bumble bees (B. vosnesenskii) collected more cranberry pollen than pollen from non-target plants, and consistently collected a higher proportion of cranberry pollen than honey bees. The results of these studies suggest that native bumble bees may be adequate for cranberry pollination in Curry County, Oregon. However, the size of bumble bee populations may vary from year to year due to climactic conditions, availability of nesting sites, and forage before and after cranberry bloom. Thus the dependability and consistency pollination services rendered to cranberry crops by bumble bees needs to be further investigated in relation to population fluxuations. / Graduation date: 2012

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