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United States Department of Agriculture

Agricultural Research Service

Research Project: BEE DIVERSITY AND THE DEVELOPMENT OF HEALTHY, SUSTAINABLE BEE POLLINATION SYSTEMS

Location: Pollinating Insects-- Biology, Management and Systematics Research

Title: Spatial Patterns of Bee Captures in North American Bowl Trapping Surveys.

Authors
item Droege, Sam -
item Tepedino, Vincent
item Lebuhn, Gretchen -
item Link, William -
item Minckley, Robert -
item Chen, Quian -
item Conrad, Casey -

Submitted to: Journal of Insect Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 16, 2009
Publication Date: January 6, 2010
Citation: Droege, S., Tepedino, V.J., Lebuhn, G., Link, W., Minckley, R.L., Chen, Q., Conrad, C. 2010. Spatial Patterns of Bee Captures in North American Bowl Trapping Surveys. Insect Conservation and Diversity. 3:15-23.

Interpretive Summary: There is increasing concern that the numbers of native bees, the most valuable pollinators of native plants, are in decline due to pesticide application and habitat destruction and modification. To gather evidence to support or refute this claim, accurate estimates of bee numbers in natural and artificial habitats must be obtained. The most unbiased method for surveying bees are passive water and detergent filled-traps, frequently referred to as pan or bowl traps. While information has been previously gathered on the favored size and color of trap to be used in surveying, no information is available on how traps should be positioned, how far apart they should be, and how many traps should be placed in a group. This study compares results from seven studies of traps placed in trapping webs, grids, and transects in four North American ecoregions (Mid-Atlantic, Coastal California, Chihuahuan Desert, and Columbia Plateau). Over 6000 specimens from 31 bee genera were captured and analyzed. We found that 1) the per bowl capture rate of bees did not decline until distances between bowls was less than three-to-five meters; 2) the degree of clumping of bees within transects was insignificant. Thus, results indicate that interbowl distances within transects can remain relatively short without affecting capture rates and that it would be wise to disperse bowls and transects throughout a study site to cover all habitat types.

Technical Abstract: Bowl and pan traps are now commonly used to capture and survey bees (Hymenoptera: Apiformes) for research. To increase the efficiency of this technique, studies of how arrangement and spacing of traps affects captures of bees are needed. We present results from seven studies of traps placed in trapping webs, grids, and transects in four North American ecoregions (Mid-Atlantic, Coastal California, Chihuahuan Desert, and Columbia Plateau). Over 6000 specimens from 31 bee genera were captured from all studies. Using trapping webs and distance tests, we found the per bowl capture rate of bees did not decline until distances between bowls became less than three-to-five meters. Minor clumping of bees within transects was detected, with 26 of 56 transects having Index of Dispersion values that conformed to a clumped distribution and 39 transects having positive Green’s Index values. Nevertheless, degree of clumping was slight, averaging only 0.06 (the index ranges from -1 to 1) with only five values greater than 0.15. Similarly, runs tests were significant for only 5.9% of the transects. Results indicate that interbowl distances within transects can remain relatively short without affecting capture rates and that the moderate values of clumping of captures within transects indicates that it would be wise to disperse bowls and transects throughout a study site.

Last Modified: 8/2/2014
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