Pollinator Paradise Parma R & E Center
PSES
College of Agriculture
University of Idaho
Research slide shows
Bee management
Philosophy
Links
Contact us
Sampling Alfalfa Leafcutting
|
 |
University of Idaho
College of Agriculture
Cooperative Extension System, Agricultural
Experiment Station CIS 1040
Contents:
Why sample bee cells?
Using the Parma Cocoon Testing Lab
Laboratory services
Advantages of using the Parma Cocoon Testing Lab
How to collect a sample
Loose cells
Polystyrene boards
Solid wood boards without a backing
How to send a sample
How the laboratory tests cocoons
Analyzing loose cell samples yourself
Interpreting conflicts with Canadian results
Calculating how many live cells you have and how many you need
Loose cells
Wood boards
Determining percent emergence after releasing bees
Loose cells
Solid boards
Further readings
The
authors
Sampling bee populations allows you to:
 | Estimate the percentage of cells containing live prepupae |
| Determine sources of bee mortality |
| Calculate live cells per pound and total live bees produced in your field |
| Determine how many additional bees to purchase for the next season |
| Track changes in bee quality due to changes in management practices and weather, if you keep records over several years |
| Confirm that you are getting the expected live count of Canadian bees |
| Determine how advanced bees are in their development if temperature controls fail in cold storage facilities |
| Evaluate loose cells after bees have emerged and been released in the field to find out if any intact cells contain bees that developed to the pupal or adult stage but were unable to chew out of their cells. This may happen if bees experience unfavorable conditions in the spring or fall. |
Note: For information on the current status of the Parma Cocoon Testing Lab, contact the Parma Research and Extension Center (208) 722-6701 x242; jbarbour @ uidaho.edu
 |
The Parma Cocoon Testing Laboratory at the University of Idaho’s Parma Research and Extension Center opened in November 1994. Its purpose is to provide accurate estimates of the quality of bees from leafcutting bee cell samples. It can also provide an estimate of percent successful emergence and sex ratio of bee samples. Producers and pollination consultants can keep a record of their results and use this information to monitor and improve their bee populations. X-ray equipment for the Parma Cocoon Testing Laboratory was purchased jointly by the Idaho and Oregon Alfalfa Seed Commissions and the Nevada Alfalfa Seed Research and Promotion Board. There is a fee for using laboratory services. |
Note: For information on the current status of the Parma Cocoon Testing Lab, contact the Parma Research and Extension Center (208) 722-6701 x242; jbarbour @ uidaho.edu
Based on x-ray examination, the laboratory will provide you with a report containing the following information about your loose cells: | Percentages of cells with live larvae, chalkbrood, pollen balls, parasites, dead larvae, and machine damage |
| A pie chart summary of the percentages |
| Mean live cells per pound |
| A 95 percent confidence interval around the estimated mean. (There is a 95 percent chance that the live cells per pound falls somewhere between the upper and lower values of the confidence interval.) |
| Percent of live cells that successfully emerge |
| Sex ratio |
Note: For information on the current status of the Parma Cocoon Testing Lab, contact the Parma Research and Extension Center (208) 722-6701 x242; jbarbour @ uidaho.edu
An x-ray report provides more detailed information about loose cells than most growers get if they open cells themselves. The Parma Cocoon Testing Laboratory sample includes about 500 cells, more than most growers have time to open. Submitting samples to the Parma Cocoon Testing Laboratory may save you time. Usually results are ready within 2 to 3 work days. The report also provides an objective written confirmation that you are getting the live count of Canadian bees that you expect.| Note:
Cell moisture content may change after cells are punched out. This can alter estimates of live larva per pound. See “Interpreting Conflicts with Canadian Results.” |
Loose cells—Be sure that loose cells are well tumbled,
because the weight of leaf debris is
not taken into consideration in calculating live larvae per pound for
loose cells. The accuracy of your sample depends on how representative it is of the entire population
of bees. Take a handful
of cells from two or three different depths in each container to be tested. Mix these cells well in a separate container, and measure out 100 grams (3.5 ounces or about 2 cups) per x-ray to send to the laboratory. Please do not mix Canadian bee samples with local bee samples because bee quality differs greatly between sources. Polystyrene boards—Growers who buy solid polystyrene boards can punch out one or two nest tunnels per board with an Allen wrench or other straight tool. Tell the lab that your sample was hand-punched from boards rather than from tumbled loose cells so that the entire sample will be weighed to take into account leaf remains when live larvae per pound is calculated. If you know the average weight of empty boards and filled boards, you should be able to calculate the live count per board from the information the lab provides.
|
Sampling solid wood boards without a backing
Wood boards are sampled with a larval probe, which can be purchased from some suppliers of wood boards. A probe is a corkscrew wire the diameter and depth of the holes in solid wood boards. The corkscrew is glued inside a pen case.Larval probes work best when most cells contain live prepupae that have spun their cocoons. If many cells contain pollen balls, it may be difficult to separate individual cells. The probe itself may also stab some live larvae, making it difficult to know if the larva was live or dead before sampling. Despite these problems, a larval probe is the best method we currently have to estimate bee quality in solid wood boards.
The bee board is probed most easily if it is standing upright. Insert the probe into a hole by pushing gently and turning counterclockwise until it can go no deeper. Then pull straight out to remove the cells. Remove the cells from the probe by holding them gently and turning the probe clockwise. If the probe has not cut through the leaves and cocoon of a cell so that the larva is visible inside, you may need to use the point of the probe or a knife to cut open the cocoon.
Count the number of live larvae each time that you probe a hole. Try
to sample one hole in each of at least 50 boards to get a representative
sample of your bees. You also should estimate the percentage of filled
holes per board.
Top of page
If you send more than one sample, clearly label each sample so that they will not be confused. Place the paper bag in a container to prevent crushing during shipping. A clean margarine container, coffee can, or similar container will do. Insulate with packing material such as plastic peanuts or crumpled newspapers.
Ship your package via U.S. mail, UPS, or Federal Express, or deliver it by hand. Try to avoid shipping by surface mail if temperatures are expected to be especially hot or cold. Clearly mark the outside of the package “LIVE MATERIAL. AVOID EXTREME HEAT OR COLD.”
Address samples to:
Parma Cocoon Testing Laboratory
Parma Research and Extension Center
29603 U of I Lane
Parma, ID 83660
Contact the Parma Cocoon Testing Laboratory for current fees and
include payment with your sample. Call 208-722-6701 weekdays, 8
a.m.-12 p.m. and 1 p.m.-5 p.m. mountain time.
Note: For information on the current status of the Parma Cocoon Testing Lab, contact the Parma Research and Extension Center (208) 722-6701 x242; jbarbour @ uidaho.edu
Loose cells—When ready to be processed, the sample is divided into five subsamples of 10 grams each, laid on contact paper, and x-rayed. X-rays are evaluated, and cells whose contents are unclear are opened for confirmation. Results are then recorded, tabulated, and graphed. A copy of the results is sent to you along with the x-ray.
Boards—For samples hand punched from solid polystyrene boards, the entire lot is weighed. Loose leaf debris is separated from good cells and weighed. The sample is divided into 10-gram subsamples, and five of these subsamples are chosen at random for x-ray analysis. This avoids a potential bias for leaving heavier cells (e.g., pollen balls) in the bottom of the pile. Crushed cells containing dried prepupae with no mold are counted as live. When calculating live larvae per pound, average live larvae per subsample is divided by 10 grams plus a fraction of the weight of leaf debris, which depends on the number of 10-gram subsamples. This is multiplied by 454 to convert grams to pounds.
Emergence and sex ratio—Samples are accepted for emergence/sex ratio testing between January and April. The cells are first x-rayed as described above. Cells that appear live in the x-ray are removed from the contact paper and placed in small plastic trays with individual wells for each cell. The trays are labeled with the grower’s name and the date the test is begun. Trays are stored at 85° to 88°F until all live bees have cut through their cells.
Although bees stored at 41°F for 6 months should complete emergence
in about 30 days, bees stored for only 3 or 4 months may take several weeks
longer to complete emergence. When emergence is complete, the sex of emerged
bees is recorded. Cells that have not emerged are opened to determine at
what stage the bees died. A report is mailed as soon as the data are compiled.
Top of page
If you analyze your own bee samples, select a representative sample in the manner described above. Weigh out 0.35 ounces (10 grams) of cells instead of 3.5 ounces. This should be about 100 cells. Alternatively, count out 100 cells and then weigh them. It is a good idea to take several such samples and calculate average live cells per ounce.
Use a small, sharp utility knife, razor blade, or pen knife to cut the cap off each cell or to carefully slice across the length of the cell just below the surface of the leaves. Cut through the leaves and cocoon but not into the larva itself.
Live larvae will be full and white and will spring back when pressed with a pencil point. If you are not sure whether the larva is alive, lay the larva on the table and briefly press on the head area until it is nearly flat. If it springs back after you release the pressure, then the larva was healthy. If the head area stays depressed, the larva was dead or dying.
Count the live larvae in your sample.
Percent live larvae = number of live larvae x 100.If you wish to calculate live larvae per pound, use one of these formulae, depending on your measurement units:
number of cells opened
Live larvae per pound = number of live larvae x 16
ounces cells opened= number of live larvae x 454.
grams cells opened
If the percentages of live larvae for the two samples are close, the quality of bees has not changed since the Brooks Lab sample. If the percentage of live larvae has decreased, check to see if the percentage of dead larvae has increased. Mortality may have occurred from unfavorable conditions in your storage facilities or from damage incurred during sampling. Consider these possibilities before you blame your supplier.
Live larvae per pound may change over time as cell moisture content changes, without a change in the number of live bees. If the number of cells per 10-gram sample has increased between samples, cells may have dried since the last test. Cells per pound will have increased, but total pounds of cells purchased will have decreased.
Conversely, if the number of cells per 10-gram sample has decreased between samples, cells may have picked up moisture since the last test. Cells per pound will have decreased, but total pounds purchased will have increased. In either case, if the percentage of live larvae is similar between the two samples, the total number of live bees purchased (or gallons of live bees purchased) has not changed. The total pounds of cells and the number of live bees in your purchase should be determined at the same time as live larvae per pound.
Also remember that there is natural variability between samples because
the cells themselves vary. The Parma Cocoon Testing Laboratory calculates
a confidence interval (an upper and lower value) around the estimate of
live cells per pound that takes into account variability between 10-gram
samples. If another estimate falls within this interval, the two estimates
are not significantly
different.
The more variable the subsamples, the greater is the difference between
the upper and lower values of the 95 percent confidence interval. The true
variability may be even greater, because one 50-gram sample of cells may
not be representative of a very large lot. Also, different people reading
the same x-ray may disagree about the contents of a few cells. All of these
factors can explain differences in the results from different laboratories.
Top of page
 |
Method 1—Multiply your estimate of live larvae per pound of loose cells by the total weight of loose cells that you have purchased or punched out to calculate the total number of live larvae that you expect to emerge in the spring. You should weigh your total cells at the same time that you estimate live larvae per pound so both weights are consistent with the moisture content of the cells. Divide by 10,000 to get the number of gallons of live larvae. |
|
Method 2—Estimate the total volume of cells that you have by
counting how many 5-gallon buckets or other containers of known volume
they will fill. Multiply this total volume by the percentage of live larvae
divided by 100 to get total volume of live cells. A gallon of live larvae
has approximately 10,000 cells. (You can get a more accurate estimate of
cells per gallon by counting the number of cells in a 1-cup measuring cup
and multiplying by 16, the number of cups in a gallon. Expect about 625
cells per cup.)
|
To determine how many gallons of female bees you have, multiply the
number of live emerged bees by the percentage of females divided by 100.
Aim to release 7,000 to 17,500 females per acre (the equivalent of 2 to
5 gallons or 20,000 to 50,000 live bees. This assumes an average of 35
percent females in the population.)
| Suppose the results of an emergence test indicate that 92 percent
of live larvae will emerge
from your sample and suppose that you have 52 gallons of loose cells: 52 gallons x 0.92 = 47.8 gallons live adults.Suppose 44% of the emerging bees are females: 478,000 live adults x 0.44 = 210,000 females.If you are aiming for the equivalent of 4 gallons of live bees per acre (40,000 bees), you want to use 14,000 females per acre (40,000 bees x 0.35). Thus, 210,000 females should be adequate to pollinate 15 acres: 210,000 females ??14,000 females per acre = 15 acres.Note that by considering the percentage of emerged females, which is greater than the average of 35 percent, we determined that these bees should adequately pollinate more acres than was indicated by the number of total live larvae. |
Suppose you average 1.65 larvae per hole. A full board would have
about
1.65 larvae per hole x 2,096 holes per board= 3,458 live larvae per board.Since 1 gallon is defined as 10,000 live cells, you have the equivalent of 0.35 gallons of bees per boardTo have 20,000 live bees per acre you will need 20,000 live bees per acre ??3,458 live larvae per board = 5.8 boards per acre. |
To sample emerged loose cells, wait until no new bees emerge from your trays. Take a handful of cells from each shelter, or from a selection of trays in your incubator, and mix them together in a container. Randomly select 100 cells from the mixture, and check to see if there is an emergence hole.
If you check 100 cells, the number of cells with holes is an estimate
of percent emergence and should be close to the percentage of live larvae
calculated during the winter. If more cells than expected are still sealed,
you may want to open some to see if dead pupae or adults are inside. The
Parma Cocoon Testing Laboratory will provide an x-ray and count of emerged
cells for growers who would like a written assessment.
Top of page
Order from Bulletin Office, Cooper Publications Building, Washington State University, Pullman, WA 99164-5912,How and Where Were They Raised? Critical Management Considerations in Megachile. Proceedings of the 26th Northwest Alfalfa Seed Growers Winter Seed School. pp. 27-35.
(509) 335-2857.
Top of page Pollinator Paradise
Parma R & E Center
PSES College of Agriculture
University of Idaho
Research slide shows
Bee management
Philosophy
Links
Contact us
Revised