Enhancement of pollination by native bees in blueberries and cranberries
Pollination is critical for production of blueberries and cranberries. In the Pacific Northwest, growers rent honey bee hives for pollination. However, honey bees do not perform as well as native bees in these crops due to prevailing weather conditions during bloom and due to their preference for other flowers in which nectar is easier to access. In contrast, native bees forage in wind, rain, and on cloudy days. Also, economically, native bees are less expensive and invasive. Hence, the study was conducted to determine strategies for enhancing populations of native bees for increasing pollination and improving yield and grower profit.
- 1. Estimate native bee pollinator species diversity and abundance in berry fields.
2. Compare honey bee and bumble bee foraging behaviors in berry fields.
3. Evaluate the impacts of insecticide sprays on native bees.
4. Examine strategies for enhancing native bees in berry fields.
5. Build capacity in growers to identify, protect and enhance native bee pollinators in their fields for increasing berry production.
Objective 1: Estimate native bee pollinator species diversity and abundance in berry fields.
To monitor native bee abundance in blueberry fields, blue vane traps were utilized on three farms for weekly trapping over a period of six weeks during crop bloom. Traps were placed monthly thereafter throughout summer. Bee specimens that were trapped were preserved and identified, and data compilation with information about floral resources in blueberry fields, both within the crop rows and in adjacent hedgerows and naturalized areas on the farms, is in progress. Representative specimens of each taxa collected are being prepared for reference collections.
Our observations indicate that numbers of bumble bees and honey bees trapped during bloom (May) were comparable. Excluding bumble bees, there were four times as many native bees as honey bees trapped during bloom. In summer, bumble bee abundance increased drastically due to the production of workers which forage on other crops in the area. Post blueberry bloom, we observed bumblebees and other native bees on weeds in Asteraceae (false dandelion), and on Rosaceae (Rubus, Spiraea), Fabaceae (clover, lotus), and Lamiaceae (mint, pennyroyal, nettles).
Blue vane traps were placed at four research sites between two cranberry bogs and the surrounding areas. At each site, two traps were set. Each trap was set out for 24 hours. Sampling was conducted sixteen times over the two-year study.
All together, 1,337 specimens belonging to 5 families, 13 different genera and over 25 species were captured. Apidae and Halictidae are the dominant families represented in Oregon cranberry agroecosystems. Bombus spp., Agapostemon spp. and Lasioglossum spp. were trapped in greater abundance than honey bees. While Lasioglossum could not be identified to species, Agapostemon was overwhelmingly comprised of A. texanus (99%) while the remainder was A. virescens—a species common to the Willamette Valley. The genus Bombus (bumblebees), however, was more diverse.
Objective 2: Compare honey bee and bumble bee foraging behaviors in berry fields.
Two-minute counts were performed along the same section of a cranberry bog throughout the study. Counts were made every other hour in 2008 and once every hour in 2009. The bees sighted along transects were visually identified and recorded along with the wind speed and temperature for the time interval. Our observations provide insights on peak flight activities of honey bees and bumble bees based on wind speeds and prevailing temperatures
In a separate study, honey bees and bumble bees were compared with other pollinators including syrphid flies, and andrenid bees during 5 minute visual observations made while walking in the bogs once per week at four different cranberry farms in Coos and Curry counties. Honey bee abundance was observed to be highest due to the presence of hives rented by growers.
Although, honey bees appear to be more abundant in cranberry fields, grower observations suggested that their role in pollination was limited. To evaluate pollinator performance, we used cages to compare pollination by honey bees (Apis mellifera), bumble bees (Bombus vosnesenkii), with the absence of animal pollinators in cranberry production. These treatments were compared with two types of controls, “open pollination,” or patches of cranberries in which every type of potential pollinator was allowed to visit. One open pollinated location was near the cages in order to simulate circumstances that the plants within the cages suffered; including some lack of water, nutrients, and sunlight. The second open pollinated location was far from the cages in order to compare with plants receiving normal levels of water, nutrients, and sunlight. Our results indicated that yields in bumble bee and honey bee cages were comparable and higher than yield in cages with no pollinators. However, yield in these cages was lower compared with open pollination locations due to cage effect.
The weight of honeybee pollen gathered from honey bee hives on cranberry farms varies considerably depending on progression of bloom, type of pollen trap used, and which hive it was gathered from. To assess pollen collection by honey bees, in 2009, pollen was collected from a group of honey bee hives placed on a cranberry farm in Curry County, Oregon. We recorded a range in pollen weight depending on when pollen was collected and the type of pollen trap used. A more extensive study for the most efficient and consistent pollen traps will be conducted in 2010.
Pollen from 35 species of plants found in areas surrounding cranberry bogs was collected to compile a reference collection. Characterization of pollen in pollen loads using acetolysis is in progress.
Objective 3. Evaluate the impacts of insecticide sprays on native bees.
The toxicity of pesticides on the bumble bee, Bombus vosnesenskii, was assessed. Blueberry plant material was collected from an unsprayed planting at an Oregon State University farm. The pesticide compounds tested were Admire 2, Success and Pristine. These products are used to control aphids, leaf rollers and fruit rot. Pesticide treatments consisted of the minimum, maximum and 2X maximum recommended field rate listed for the insect pest. Each treatment was replicated six times. Pesticides were applied to plant material within cages using a Potter precision laboratory spray tower prior to exposure to bees. Mortality was assessed after 24, 48 and 72 hours by recording the number of dead bees within each cage.
The study documented that all rates of Admire resulted in > 75% mortality. With Pristine, the mortality ranged from 17 to 58%. Least mortality was observed with Success to which bumble bees exhibited a reverse response in relation to dose
Objective 4. Examine strategies for enhancing native bees in berry fields.
To establish baseline information for comparison with strategies for drawing native bees to targeted fields, qualitative and quantitative data measurements were made of native bee foragers in randomly selected 10-m2 plots in and around blueberry fields. Each plot was given a numerical score to reflect proportion in bloom and five minute counts were performed recording the number of Bombus spp., Apis mellifera, and other native bees (Apidae, Halictidate, Megachilidae, etc.). Plant composition of each plot was recorded, and these data are being utilized to examine the patterns and relationships between bloom and native bee abundance. The phenology of bee attractive, heavily foraged plants will be utilized to design the flowering hedgerows portion of the experiment which will be performed in the summer of 2010.
Objective 5. Build capacity in growers to identify, protect and enhance native bee pollinators in their fields for increasing berry production.
Native bees that are common in blueberry and cranberry fields during bloom were photographed and development of a pictorial identification key is in progress. A bee identification workshop has been organized for cranberry growers on February 3, 2010. Feedback from the workshop will be used for organization of a similar bee identification workshop for blueberry growers.
In conjunction with collecting data from blueberry fields in the summers of 2008 and 2009, discussions with growers have led to characterization of existing management practices with regard to preservation and enhancement of native pollinators at the landscape level. In collaboration with the farms that will participate in the experimental phase, hedgerows, margins and between-row plantings of attractive forage source plants are being designed for implementation in the summer of 2010.
Impacts and Contributions/Outcomes
At the Annual Blueberry Growers’ and the Annual Cranberry Growers’ meetings in January 2009, we gave talks during which research plans for the year were presented to all attendees. Subsequently, we met with growers to select specific sites for trap placement for assessment of the native bee diversity in spring-summer 2009.
The diversity and abundance portion of this study is providing a baseline measurement and description of the native bee fauna in blueberry and cranberry fields. This information will allow farmers to recognize important native pollinators in their fields. Information about the relationship between native bee numbers and floral resources will be used for design of the experiments to be performed in 2010, and those results will shape the recommendations and materials that are made available to shareholders, including planting schemes designed with sequential bloom in mind to provide pollinator food sources all season long.
Presentations made related to blueberry and cranberry pollination research:
Evaluating pollination by bees for enhancing blueberry production, Blueberry Growers’ Meeting, Corvallis, OR, January 2009.
Native bees and honey bees associated with cranberry production, Annual Cranberry Growers’ Meeting, Bandon, OR, January 2009.
Honey bees and bumble bees in Oregon cranberry bogs, Oregon State University 1st Annual Student Research in Entomology Symposium, Corvallis, OR, February 2009.
Native bee and honey bee foraging in Oregon cranberry, Entomological Society of America 57th Annual Meeting, Indianapolis, IN, December 2008.
Publications related to blueberry and cranberry pollination research:
McKenney, M., Rao, S. and Stephen, W.P. 2009. Pollination in Cranberries on the South Oregon Coast: Honeybees and Native Bees. South Coast Grower News. 3(1):3-5
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