From Bee Craft: July 2009
Dewey M Caron, PhD, University of Delaware (retired)
A summary of Dr Caron’s presentation to the National Honey Show 2008
CCD, Nosema and mites are significant factors in the downward trend in numbers of honey bee colonies both in the US and Europe, raising deep concerns for crop pollination, (see discussion of bee loss numbers on www.maarec.psu.edu).
Although of utmost importance, the honey bee is but one insect pollinator. Native bee populations too are considered to be in decline in North America (see The Status of Pollinators in North America [National Research Council 2007 -hwww.Sciencemag.org: DOI: io.ii26/science.ii27863;
With funding from USDA SARE (United States Department of Agriculture Sustainable Agriculture Research and Education Program), the University of Delaware and the Delaware Department of Agriculture have initiated a cooperative project in the cucurbit farming region of Delaware and Maryland directed towards identifying and facilitating the process of conserving native pollinators.
While honey bees are social and generalists in their flower visitation behaviour (workers from a bee colony may visit 200 or more plant species in a season), the over 4000 North American species of native bees are more likely to be specialists in their flower visitation and therefore in their pollination of plants.
Bumblebees are seasonally social but most native bees are solitary and adults only during a limited time of the season. The vast majority nest in the ground (eg, ground mining and digger bees) but a few are cavity nesters (carpenter and Osmia bees). A few species are being increasingly exploited, along with honey bees, by humans for their pollination services. These include bumblebees in glasshouses or orchard bees (cavity nesters) for fruit pollination and ground-nesting alkali bees for alfalfa pollination.
The broad objectives of our four-year ‘Farming for Native Bees’ project are the following:
- develop a long-term bee-monitoring network
- recommend bee-friendly practices to farmers
- update land retirement and conservation programs to include bees
- enhance pollinator awareness in the farm and broader community through public education efforts.
NATIVE BEE SAMPLING
We have relatively few records of the native bees of Delaware. Our project is using both passive (pan traps) and active (netting) methods to determine which bees are present during the flowering season for cucurbits and organic farmers of our region.
The passive method uses a 100 m transect adjacent to designated farms utilizing 15 pan traps. Pan traps are 3.25 oz Solo™ Brand souffle cups, painted with blue, yellow and white fluorescent paint following a standardized method developed by Droege.
Netting is conducted along two 50 m x 2 m transects in cropping fields. Flower visitors are netted for 15 minutes during peak foraging hours with a standard aerial net. Sampling days are selected during the peak bloom of the crop, on days ranging from sunny to partly cloudy, and the estimated number of open blooms noted.
A total of 75 farm sites have been sampled from 2006-2008, the majority for at least two years. Sites represent both conventional cucurbit (primarily cucumber and water melon crops) and organic farms, along with all State Parks that have agricultural production areas and two museums with agricultural land. Co-operator fields are being surveyed on a four-week cycle to assess native bee populations through the season and at different stages of crop development. Adjacent land to co-operating growers is defined and determined using Arc-GIS and land use/ conservation areas categorized and ground verified as to crop/use content during the sampling period.
IDENTIFYING BEE SAMPLES
Our bee samples are processed and identified using keys posted for bees on the USGA (University of Georgia) website. One exciting aspect of our project is that we have been able to identify and post taxonomic determination and collection locations with relatively little delay for the majority (>95%) of our collection data.
During the 2006 pilot study and the 2007 sample year, 6500 native bee specimens were collected. They represent a total of 92 species, almost half of the estimated 194 species that might occur in the region. Sampling in 2006 and 2007 revealed 16 new bees not previously recorded in the state. In 2008, 166 transects were sampled and specimens are currently being processed and identified. For an example, you can see the entry for the native pollinator Mellisodes bimaculataat
Beyond merely obtaining a native bee database, a major project goal is to conduct assessments on participating farms and, together with these cucurbit farmers, develop a conservation plan for each establishment.
In 2008, assessments were conducted on seven participating farms. In addition to our bee species richness and abundance data collection, assessments involved gathering information on co-operators’ farming practices to develop an intensive record for the following:
- current crop production practices/needs
- land use history and conservation philosophy
- pesticide use and practice/philosophy
- bee nesting sites and potential for augmentation
- non-crop land use management — land cover, soils, benefits and needs
- participation in governmental/private land conservation opportunities.
With farm assessment and bee diversity/abundance data, we will develop bee-friendly practices that might be implemented by farmers. Since growers can benefit from governmental/private conservation programs (such as USDA NRCS [National Resources Conservation Service]) we are working with these agencies to ensure that our findings are incorporated into such programmes.
Toward this end we have co-operatively prepared two publications: Farm Management of Native Bees and Delaware Native Plants for Native Bees. These richly detailed manuals describe bee pollination conservation management. By the end of our funding cycle, we expect to have a set of recommendations for cucurbit farmers that will ensure native bees become part of their pollination management and begin expansion to other farming/public and private land management sectors of similar native bee conservation principles and practices. (See the website for publication copies and program updates: www.dda.delaware.gov/plantind/pollinator.shtml).
PROMOTING POLLINATOR DIVERSITY
It is clear that honey bees are the workhorse of crop pollination but it is also abundantly clear that they cannot meet all our pollination needs. Recent studies of conservation practices and the benefits of pollinator diversity in cropping systems illustrate the need to work to promote pollinator diversity and conservation of native pollinators to our benefit and health.
[Presentation at the National Honey Show, 31 October 2008, sponsored by Bee Craft.]