William P. Stephen

Oregon State University, Corvallis, Oregon, United States

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Publications (19)4.64 Total impact

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    ABSTRACT: Abstract Native bees are important ecologically and economically because their role as pollinators fulfills a vital ecosystem service. Pollinators are declining due to various factors, including habitat degradation and destruction. Grasslands, an important habitat for native bees, are particularly vulnerable. One highly imperiled and understudied grassland type in the United States is the Pacific Northwest Bunchgrass Prairie. No studies have examined native bee communities in this prairie type. To fill this gap, the bee fauna of the Zumwalt Prairie, a large, relatively intact remnant of the Pacific Northwest Bunchgrass Prairie, was examined. Native bees were sampled during the summers of 2007 and 2008 in sixteen 40-ha study pastures on a plateau in northeastern Oregon, using a sampling method not previously used in grassland studies-blue vane traps. This grassland habitat contained an abundant and diverse community of native bees that experienced marked seasonal and inter-annual variation, which appears to be related to weather and plant phenology. Temporal variability evident over the entire study area was also reflected at the individual trap level, indicating a consistent response across the spatial scale of the study. These results demonstrate that temporal variability in bee communities can have important implications for long-term monitoring protocols. In addition, the blue vane trap method appears to be well-suited for studies of native bees in large expanses of grasslands or other open habitats, and may be a useful tool for monitoring native bee communities in these systems.
    Journal of Insect Science 01/2012; 12:108. · 0.88 Impact Factor
  • Sujaya Rao, William P. Stephen
    Entomological Society of America Annual Meeting 2011; 11/2011
  • Kimberly Skyrm, Sujaya Rao, William Stephen
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    ABSTRACT: Bumble bees are important pollinators for both native and agricultural plants. However, their populations are currently in decline due to a reduction in the availability and abundance of food resources. Mass-flowering agricultural landscapes are considered to be important for bumble bees, but bloom time can be a limiting factor given the extended annual colony life cycle of bumble bees in temperate regions. The objective of this study was to examine the individual and colony-level pollen foraging behavior of bumble bees in a late season, mass-flowering agricultural crop. Fields were surveyed over two years to determine the abundance of foragers on flowers and the foraging activity of colonies placed adjacent to red clover. Of the six Bombus spp. observed foraging on red clover flowers, B. vosnesenskii workers predominated (P < 0.01). At the colony level, there were no significant differences in the average duration of pollen foraging trips (P=0.90; P=0.56), but there was a weekly increase in the percentage of trips made for pollen during both years (P=0.04; P=0.03). The amount of stored pollen in colonies increased each week and there was a positive linear relationship with colony size (P=0.01). Of the seven different plant pollens stored within colonies, overall a higher proportion of red clover pollen was collected, compared to the other plants (P < 0.01). Conservation and land management schemes used to enhance and sustain bumble bee populations should consider incorporating mass-flowering agricultural landscapes such as red clover.
    Entomological Society of America Annual Meeting 2011; 11/2011
  • Sujaya Rao, William P. Stephen, Chiho Kimoto
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    ABSTRACT: The western bumble bee, Bombus occidentalis, is included on the red list of bees by The Xerces Society. It was once a common bumble bee west of the Cascades but in the late 1990s it experienced a dramatic decline along coastal regions. The cause was speculated to be due to the introduction of pathogens from captive-bred bumble bees used for pollination of greenhouse crops. In extensive surveys conducted in western and southern Oregon, 10 individuals have been recorded since 2000. In this note, we report the collection of 49 individual B. occidentalis over two years in the Zumwalt Prairie Preserve of northeastern Oregon. This finding shows that B. occidentalis persists in northeastern regions of the Pacific Northwest, either because of geographic isolation from or potential resistance to the pathogens that decimated populations in the western part of the region. Further research is needed to determine its occurrence in other regions of its historical range to assess the extent of its decline. In addition, conservation efforts are critical for protection of this species in both agricultural ecosystems and in native habitats.
    Northwest Science 02/2011; · 0.51 Impact Factor
  • Sujaya Rao, James Strange, William P. Stephen
    Entomological Society of America Annual Meeting 2010; 12/2010
  • Kim Phillips, Sujaya Rao, William P. Stephen, Linda White
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    ABSTRACT: Cranberries (Ericaceae: Vaccinium macrocarpon), an important crop of cool, cloudy, and windy Southwestern Oregon, face the obstacle of pollination, the necessary precursor to fruit-set. Honey bees (Apis mellifera), well known as fair-weather foragers, are rented by farmers at two hives/acre to saturate the area with pollinators. Their increasing price, decreasing availability, and questionable pollinator efficacy are motivating Oregon cranberry farmers to seek alternative pollinators. Native bumblebees (Bombus sp.) forage on cranberries even under unfavorable weather conditions that keep honeybees indoors. However, their impact on cranberry pollination under Oregon conditions is not known. Our objective was to compare pollination by honey bees and bumble bees in Oregon cranberries. Colonies were connected to 1m x 1m cages and the following treatments were compared: 1) bumble bees; 2) honey bees; 3) control (no bees); and 4) open pollination (all bees). The experiment was set up in two separate cranberry beds with four replications. Pollination success was evaluated using the following parameters: berry yield (g/m2); number of berries/m2; size of berries; and number of seeds/berry. An analysis of variance indicated that for all parameters considered, honey bees and bumble bees did not differ significantly from each other (p values > 0.05). However, due to cage effect, yield in bee pollinated cages was lower than yield in open pollinated plots. Options for build-up of bumble bee populations for enhancing cranberry pollination will be discussed.
    Entomological Society of America Annual Meeting 2010; 12/2010
  • Jennifer Bergh, Sujaya Rao, William P Stephen
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    ABSTRACT: Native wetland ecosystems provide critical food resources and nesting habitats for native bees, which supply valuable pollination services. The West Eugene Wetlands in western Oregon is a 3,000-acre restoration and conservation project with a mosaic of fragmented savanna and ephemeral wet prairies. These wetlands are host to a number of rare plant and insect populations. The objective of this 3-year study was to examine the relationship between the presence of native bees and the availability of floral resources. A survey of bee diversity was conducted using visual attractant traps and timed observations; floral resources were characterized and scored by percentage in bloom. Native bee diversity was found to be correlated with forage plant diversity, most notably with ubiquitous weed plant species. Data on phenological relationships between diversity of bees, rare plant species, and invasive plant species will be presented along with the implications of these findings for restoration land management.
    Entomological Society of America Annual Meeting 2010; 12/2010
  • Kimberly Skyrm, Sujaya Rao, William P. Stephen
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    ABSTRACT: The European honey bee, Apis mellifera , provides pollination services for diverse crops, but parasites and diseases have reduced their availability and increased the cost of hive rentals. Thus, there is increased interest in evaluating the efficacy of wild bees, particularly bumble bees, as alternative pollinators. The objective of this study was to determine the effects of colony size on the pollen foraging behavior of the native bumble bee, Bombus vosnesenskii, in the presence of mass flowering resources. Lab-reared colonies, initiated by collection of wild queens, were partitioned into two size classes based on their larva to worker ratio, and placed adjacent to a flowering red clover field in western Oregon. To determine impacts of colony size on foraging behavior, individual bumble bee workers from large and small colonies were marked and observed during peak foraging periods. Data analyses suggest the duration of pollen foraging trips is greater in small colonies, when compared to large colonies. To examine resource utilization, pollen pot samples were extracted from colonies weekly, weighed, and analyzed for floral composition. A two-sample t-test indicated a significant difference in weights across size classes, during the final week of the study as large colonies had the greatest amount of stored pollen compared to small colonies (P=0.026). This data, along with data pertaining to floral composition will be presented. Relationships of colony size with the presence of an abundance of flowering resources, and implications for sustainability of pollination services in cropping systems and wild habitats will be discussed.
    Entomological Society of America Annual Meeting 2010; 12/2010
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    Rao Sujaya, W. P. Stephen
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    ABSTRACT: There are widespread concerns about declining populations of bumble bees due to conversion of native habitats to agroecosystems. Certain cropping systems, however, provide enormous foraging resources, and are beneficial for population build up of native bees, especially eusocial bees such as bumble bees. In this review, we present evidence of a flourishing bumble bee fauna in the Willamette Valley in western Oregon which we believe is sustained by cultivation of bee-pollinated crops which bloom in sequence, and in synchrony with foraging by queens and workers of a complex of bumble bee species. In support of our perspective, we describe the Oregon landscape and ascribe the large bumble bee populations to the presence of a pollen source in spring (cultivated blueberries) followed by one in summer (red clover seed crops). Based on our studies, we recommend integration into conservation approaches of multiple agroecosystems that bloom in sequence for sustaining and building bumble bee populations.
    Psyche A Journal of Entomology 01/2010;
  • Sujaya Rao, Oksana Ostroverkhova, William P. Stephen
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    ABSTRACT: Worldwide, concerns about declines in populations of native bees have generated interest in bee census studies. For continued assessment of native bee status there is urgent need for an effective sampling technique. At Oregon State University, during a monitoring study on an unrelated insect, we serendipitously discovered that a particular blue vane trap served as a 'supernormal stimulus' for native bees. In subsequent studies the traps captured over 70 native bee species in 23 genera in 4 families. The objective of this study was to determine the basis of the attraction of the traps to native bees. We compared bee captures in blue traps with captures in a diversity of colored and fluorescent traps. Transmission, reflection, absorption, and UV-induced fluorescence of vanes were measured using various light sources including AM1.5G solar simulator and spectrometers. Data analysis indicated that sunlight-induced fluorescence rather than blue maybe the key factor that serves as the 'supernormal stimulus'. Potential applications of the blue fluorescent vanes for manipulation of bee behavior will be presented.
    Entomological Society of America Annual Meeting 2009; 12/2009
  • Kimberly Skyrm, Sujaya Rao, William Stephen
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    ABSTRACT: Bumble bees are social insects that are key native pollinators in the US. Their colonies require a continuous supply of high quality pollen and nectar to fulfill the dietary needs of developing larvae. When food resources are scarce, workers are known to eject larvae, though qualitative and quantitative information about larval ejection behavior are lacking. The objective of this study was to determine the impact of food resources, both pollen and nectar, and their abundance, on the larval ejection behavior in colonies of the native bumble bee, Bombus vosnesenskii. Lab-reared colonies, initiated by the collection of wild queens, were assigned in separate experiments to four pollen and nectar treatments (none, low, standard, high) using a randomized block design with five replications. Larval ejection occurred in all pollen and nectar treatments. An analysis of variance test indicated that there was no significant difference in larval ejection across all treatments in both pollen (P=0.69) and nectar (P=0.85) experiments. However, overall larval mortality (larval ejection and dead larvae within the colony) was found to be significantly higher in colonies exposed to no pollen (P < 0.01) and no nectar (P < 0.01) compared to the other treatments. Implications of the responses of bumble bee colonies to limited food resources, and the critical need for adequate and continuous pollen and nectar resources for sustainability of pollination services in cropping systems and wild habitats will be discussed.
    Entomological Society of America Annual Meeting 2009; 12/2009
  • Melissa McKenney, Sujaya Rao, William P. Stephen
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    ABSTRACT: Pollination is critical in cranberries for good fruit size, conformation and yield. Honey bees, Apis mellifera, are presently used to service cranberries, but their performance may be limited due to their tendency not to forage during adverse weather and lack of loyalty to the crop. The objective of this study was to examine native bee fauna and compare foraging by native bees and honey bees in cranberries. Blue vane traps were used to estimate native bee diversity and abundance in four cranberry farms on the southern Oregon coast. At the site with the harshest weather, two minute counts were taken; temperature and wind speed were noted along with any bees foraging on bloom. At the same site, honey bees and bumble bees were captured and their pollen loads removed for composition analysis. Of over five-hundred bees trapped during cranberry bloom in 2008; 4 families, 13 genera and over 26 species were represented. The genera that were most abundant were: Agapostemon (35%), Bombus (15%), Evylaeus (14%), and Synhalonia (10%). While 5 Bombus species were collected, the two closely related species B. vosnesenskii and B. caliginosus comprised >70% of the bumble bees. The two-minute count data revealed a strong correlation between high wind speed and foraging by Bombus but not by A. mellifera. The pollen data has yet to be analyzed. Implications of this study will be discussed.
    Entomological Society of America Annual Meeting 2009; 12/2009
  • William P. Stephen
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    ABSTRACT: Asian ladybug (semitransparent blue) and Japanese beetle (semitransparent yellow) insect traps (Springstar™) were tested for their utility in studies on bee diversity. The unscented traps were placed at four diverse ecological sites in Oregon in 2004 for approximately 48 hr and catches identified. Trap vanes were highly UV-A and UV-B reflective. The bee catch was diverse with a total of 369 bees, in 17 genera in five families. Bee captures were consistent with bee fauna at each site during the test periods. The semitransparent blue yielded an average of 17.3 bees/trap/day and the yellow 5.75 bees/trap/day. Bombus spp. made up 62.1% of all the bees captured, followed by the halictines (23.8%). It was surprising that Apis was virtually absent from all traps in all zones even though they were abundant in the immediate proximity of each trap. The current study is the first one in which colored traps captured sizeable numbers of bees: 1) in the absence of a pheromone or other attractant; 2) over a short time period of time (48 hr); and, 3) in a selective manner. These studies suggest that a modified SpringStar™ semitransparent blue trap may be a valuable tool in future studies on bee diversity, distribution, seasonal abundance, and bee foraging behavior.
    Journal of the Kansas Entomological Society 09/2009; · 0.55 Impact Factor
  • William P. Stephen
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    ABSTRACT: The efficacy of sweeping and vacuuming as methods of sampling native bees were compared to those of passive blue and yellow translucent-vane traps located adjacent to a highly attractive forage source, Helianthus spp. (Asteraceae). A total of 35 species of native bees belonging to 12 genera were caught during September, 94% in the passive blue-vane traps, 63% by sweeping, and 54% by vacuuming and yellow-vane traps. Overall, 55.7 % of all the native bees trapped in the study across the four treatments were collected in the blue vane traps. There were almost double the number of species, and over five times more individuals in blue vane traps than in the yellow. Agapostemon virescens (Fabr.) was the predominant species collected across all methods (400 of 1208). The majority of females (> 99%) captured in the blue vane traps lacked pollen suggesting that the bees may have been diverted by the reflected light from the trap during their flight to the floral sources rather than on their return flight to the nest. Very few Apis mellifera (L.) were taken in the traps, whereas they dominated in sweeping and vacuuming samples. These studies suggest that the blue vane traps can serve as an effective sampling tool for bee diversity studies in proximity to stands of intense floral competition.
    Journal of the Kansas Entomological Society 01/2009; · 0.55 Impact Factor
  • Sujaya Rao, William P. Stephen
    Crop Science - CROP SCI. 01/2009; 49(6).
  • Kimberly Skyrm, Sujaya Rao, William Stephen
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    ABSTRACT: While honey bees have provided pollination services for a diversity of crops, two mite species and the recent colony collapse have reduced their availability. This has increased dependence on native bee pollinators but limited information is available regarding their foraging efficiencies. This study was conducted to examine the foraging behavior of native bumble bees in red clover seed production fields in Oregon, where producers typically stock honey bee hives for pollination. The study addressed the following: 1) Are native bumble bee and managed honey bee pollen-collecting foragers equal in number? 2) Does the foraging behavior of native bumble bees vary with colony size? The bumble bee species used in this study was Bombus vosnesenskii. For comparing bumble bees with honey bees, counts of bee foragers were made during two-minute visual observations through red clover bloom. The results indicated temporal differences as honey bees were greater in abundance early in the season (p=0.01), while bumble bees were more abundant late in the season (p=0.004) with a larger proportion observed carrying pollen (p=0.04). To determine the impact of colony size, individual bumble bee workers from large and small colonies were marked and observed during peak foraging periods. Data analyses suggest considerable variation in frequency and duration of foraging trips. Observations of marked workers in adjacent red clover fields provided additional insights on distances traveled from the nest. These data will be presented, and the potential use of B. vosnesenskii for pollination of red clover for seed will be discussed.
    Entomological Society of America Annual Meeting 2008; 11/2008
  • American Entomologist. 01/2007; 53(2).
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    Melissa McKenney, Sujaya Rao, William P. Stephen
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    ABSTRACT: Many cranberry growers on the Oregon coast are well aware that good pollination is necessary for quality fruit set. Multiple visits to the flower deliver more pollen, which can increase the percentage fruit set, number of seeds per berry, and mature berry weight. The better a bee is at delivering pollen to the flower, the fewer the number of visits required for adequate pollination. Typically growers rent hives of the European honeybee for cranberry pollination. However, honeybees have exhibited a general preference for lotus, gorse, other weeds and native plants over cranberry flowers. As a result, growers must bring in enough hives to saturate the surrounding area so that at least some of the honeybees will have no choice but to forage in cranberry beds. In addition, honeybees forage primarily in fair weather. Multiple studies have shown (and many people have observed) that honeybees will retreat to their hives once it begins to rain. Often, they will retreat even when the skies become overcast, which is not ideal behavior for working in stormy coastal weather. Further, with the recent concerns about Colony Collapse Disorder, attack by mites and other diseases, the supply of available hives has decreased. This shortage brings to light the need for an alternate pollinator—a native species that is not susceptible to the ills of honeybees. In the Pacific Northwest, there are over 200 species of native bees. Those species native to Oregon are acclimated to Oregon weather. Several species of bumblebees begin foraging hours before honeybees are active, and cease foraging at dusk when the honeybees have already been inactive for an hour or two. The advantages of having bees forage longer hours are obvious—the more time they spend foraging, the more flowers they will pollinate. In addition, Oregon's native bee species are often sighted foraging when it is drizzling while the warm-weather preferring honeybees are in their hives. Currently, little is known about the number and diversity of bee species present on the southern Oregon coast. This information is required for determining whether a better pollinator than honey bees is available for cranberries. By determining which species are present during bloom it will be possible to select a species that flies during bloom, and one that is also loyal to cranberries.
  • Kimberly M. Skyrm, Sujaya Rao, William P. Stephen
    Apidologie 43(1). · 2.16 Impact Factor