Trap Height and Bee Captures, A Little Investigation
- Trap Height and Bee Captures, A Little Investigation
Summary written by Sam Droege, who also identified the genera. Traps set, run, and specimens processed by Andrew Webber and Sue Boo. Everyone works in the USGS Bee Inventory and Monitoring Laboratory.
Internet Age Executive Summary: Big bees prefer to die in traps set higher off the ground. Small bees prefer to die in traps set low off the ground. More work is needed to define and clarify the extent of these patterns.
A Little Introduction
Height of bowl or pan type traps above the substrate can affect the number and type of bees captured. Factors such as absolute height, trap type, species present, and height of surrounding vegetation all likely impact the presence and numbers of bees. We explored this a bit in June with a small study looking at the differences in a set of white 12 ounce plastic drinking cup traps (commonly used in glycol traps) and outline the results below.
Setup and Methodology
· Location - The grounds of Beltsville Agriculture Research Center in Beltsville, MD USA
· Dates run were from June 14 – 17, 2011
· 5 sites were chosen in sparse fields and lawns near Building 308
· Weather was in the Upper 80s to Lower 90's F throughout
· A rain even occurred on the evening of the 16th that knocked over a number of trap stands
· Analyses were conducted using bees per trap because of the effective trapping loss of some traps during the study
· The 5 sites were run continuously for 4 days with bees removed around 11:00 a.m. each day
· Trap containers were cheap 12 ounce white plastic drinking cups of the variety used to hold beer at parties
· Trap stands were lengths of plastic electrical conduit with a PVC ring attached to it that held the drinking cup
· Trap stands were set into the ground so that the top of the cup was approximately 10-12 inches off the ground
· Ground traps were simply the same 12 ounce white plastic drinking cups recessed into a hole in the ground so that approximately 2 inches of the rim of the cup remained above ground
· At each site, 10 traps of each type were alternated every 5 meters
· Water with Blue Dawn Dishwashing detergent was added to the cups so that it reached to within 1 inch of the rim
· Bees were identified to Genus
· Large bees were defined as being honeybee (Apis)/Agapostemon or larger
(See associated Excel Spreadsheet in separate email for raw data and the tables mentioned below or request from Sam Droege sdroege@...)
Table 1. A table showing all bees captured per trap in traps recessed in the ground and traps placed on stands by site and date.
Interpretation: There was a general decline in captures with date and there were substantial difference among sites in total number of bees.
Table 2. A table showing a simple subtraction of the difference between the number of bees captured/trap in ground traps from those captured in traps on stands.
Interpretation: Overall more bees were captured in ground traps with only 5 of 20 comparisons having more captures occurring in stand traps
Table 3. A table showing the percentage of all captures of bees per trap attributed to ground traps.
Interpretation: The percentage of bees captured in ground traps was relatively constant across sites.
Table 4. A table showing the total number of LARGE bees (AGAPOSTEMON AND LARGER) captured per trap in traps recessed in the ground vs traps placed on stands.
Table 5. A table showing a simple subtraction of the difference between the number of LARGE bees captured/trap in ground traps from those captured in traps on stands.
Interpretation: Large bees were captured more often in STAND traps than ground traps. There were 2 comparisons with equal numbers in ground and stand traps and only 5 of the remaining 18 comparisons had more large bees in ground that stand traps.
Table 6. A table showing the percentage of all captures of LARGE bees per trap attributed to ground traps
Interpretation: Across the 5 sites the percentage large bees in ground traps varied from 20.1% to 46.7% with a mean of 35.08%.
Table 7. A table showing the total number of SMALL bees (SMALLER than Agapostemon) captured per trap in traps recessed in the ground versus traps placed on stands.
Table 8. A table showing a simple subtraction of the difference between the number of SMALL bees captured/trap in ground traps from those captured in traps on stands.
Interpretation: Small bees were captured more often in GROUND level traps with only 4 out of 20 comparisons showing more captures in stand traps.
Table 9. A table showing the percentage of all captures of SMALL bees per trap attributed to ground traps.
Interpretation: Small bees were consistently caught more often in ground level traps than traps in stands with percentage ranging from 61.01 to 78.00 with a mean of 71.62
Table 10. A table showing the pecentage of the total captures that are LARGE bees
Interpretation: Smaller bees were caught more often than larger bees.
Table 11. A table showing the difference in the percentage capture of large bees between ground traps and traps on stands
Interpretation: Larger bees were much more likely to be captured in trap stands than in the ground traps with only 2 out of 20 comparisons showing the reverse (with 1 being equal)
Table 12. A table showing, by genus of bee, the average number of bees captured per trap for sites/ that had any captures of that genus.
Interpretation: Note the interesting differences in captures rates among the genera.
· As always, it would be interesting to see if these results can be replicated elsewhere
· This is an easy to do student/class project
· Larger bees may be more vulnerable to taller traps as they may use taller flowering plants and thus prefer to investigate taller traps
· Larger bees may be foraging over larger, more patching environments. Smaller bees may be foraging more locally on smaller, lower flowers
· Large captures of Melissodes in vane traps set a meter or more above the ground may be due to similar processes
· Location of traps almost certainly bias capture rates of different species of bees both positively and negatively in any trapping situation
· Using both taller and shorter trap heights in a survey situation could increase the species sampled, but…..since the differences are not absolute, the effort needed to put bowls on stands vs taking that same effort (and associated costs) and applying it to putting out more bowls needs to be considered
· Drinking cups recessed into the ground have the advantage of not needing a stand but having a deep well to hold specimens if using glycol, but, have the disadvantage of filling with dirt from rain splash from rain storms
· Anyone who would like to use or publish these data is free to do so
Sam Droege sdroege@...
w 301-497-5840 h 301-390-7759 fax 301-497-5624
USGS Patuxent Wildlife Research Center
BARC-EAST, BLDG 308, RM 124 10300 Balt. Ave., Beltsville, MD 20705
And a Big Herd of Sweet Goats
I used to walk in a beautiful garden
But the garden fell in love with my
And fell in love with my toes too,
Then concluded it would be smart
To just follow me home
And never move!
The same thing happened with the sun,
Then Saturn and a dozen other
And a whole near-by mountain range
With their trees and streams and fish still tied
Onto their backs -
And a big herd of sweet, lively goats.
My dear, what Hafiz is really trying to say is:
If you ever get
Come visit this Wild house -
My Celestial Verse -
Where all of us will always
So happily live.
translated by D. Ladinsky