Historically leafcutter bee nests consisted of drilled pine or fir boards, usually 3 to 4 inches by 4 to 6 inches (~7.6 to 10 centimeters by 10 to 15 centime- ters) in width, and often up to 4 feet (~1.2 meters) in length. Boards were drilled with a series of dead-end holes for nest tunnels. Such nests were extremely attractive to bees and convenient because the bees could be stored and incubated within the boards(fig- ure 7.13).
However, because the inner nest surfaces could not be exposed for cleaning, and because the boards were continually filled with bee larvae, these nests became contaminated with a fungal disease called chalkbrood (Ascosphaera aggregata). By the 1980s US beekeepers who continued to manage bees in solid boards saw significant annual losses. To reduce the spread of chalkbrood spores, beekeepers began phas- ing out solid boards on an annual basis, drilling out the tunnels to remove dead bees and leaf debris. This labor-intensive practice resulted in the term re-drill in reference to solid wood nest boards.
While re-drills were the standard American nest for many years, Canadian leafcutter producers pio- neered new nest designs that facilitated the annual removal of cells from the nest. Among these nest designs were solid wood blocks that were drilled com- pletely through, and grooved boards (often called Table 7.1
Leafcutter Management Timeline for Alfalfa Pollination in Northern States*
MONTH TASK
January Buy or sell any bees or nesting materials; check for mold growth on stored nests or loose cells.
February Last month to safely mail dormant bees in most areas. March Make a final check of equipment. Test check bee
viability if desired.
April Set up field shelters. Set up incubation room with appropriate equipment: heat source, fans, humidifier, light traps (for parasite control), incubation trays. Or, place nests in field for natural seasonal emergence. May Secure nest shelters against field predators such as
ants and earwigs by greasing the legs of field shelters. June Begin incubation to coincide with crop bloom (refer to incubation timeline). Control parasites with light traps and daily vacuuming.
July Release incubated bees. Nesting begins! Remove leaf debris from emerging cells as possible. Check field shelters for bats, yellow jackets, and paper wasps. August Second generation bees emerge.
September Remove nests from field. Begin pre-chilling bees by gradually moving the nests to a cool location (not in cold storage).
October Begin removal of cells from nests if desired, being sure to cover any loose cells with a 1-inch layer of sawdust or vermiculite. Disinfect nests and shelters. Quantify your bee population.
November Clean and tumble any loose cells. Place bees in cold storage at 35° to 40°F (1.7° to 4.4°C), 50% relative humidity for 150 to 210 days. Control parasites if bees are stored in a nonsecure area.
December Clean and repair beekeeping equipment. Submit bee samples for lab analysis.
* Timeline and months may vary by region. Bees in California, the Southwest, or southern states may require a different rearing schedule.
Figure 7.13 Leafcutter bees were historically managed in solid wood blocks drilled with nest tunnels. Because these types of nest cannot be effectively cleaned, they often become contami- nated with parasites and diseases over time, causing a decline in populations.
laminates) that consisted of a series of channels routed into the boards, which were stacked together to form a series of tunnels (figure 7.14). These nest
types were originally constructed of wood; however, today they are only commonly available as Styrofoam with fabric or foam backing material which is held in place by a series of sheet metal clamps or elastic straps(figure 7.15).
These loose-cell nests have a tremendous advan- tage because they can be completely disassembled and cleaned each season. In addition, the loose cells require significantly less space for cold storage and incubation than solid boards filled with bees. There are several disadvantages with loose-cell nests, including the potential for greater parasite problems due to the less secure backing material and the poor durability of Styrofoam nests.
Various other nest materials have been used for leafcutter bees, including paper straws and fluted cardboard consisting of a series of tunnel corruga- tions affixed to a single sheet of paper backing, which is then coiled onto itself forming a round spiral of
tunnels. Like the loose-cell nests described above, these paper and cardboard nest materials are much more prone to infestation by parasites than solid wood blocks.
A significant amount of research has been per- formed on the nesting preferences of leafcutter bees. Tunnel diameter, depth, material, color, and hole density have all been explored, and in many cases the results have been contradictory or inconclusive. General guidelines are as follows: tunnels should be between 15/64 and ¼ inch in diameter (6 to 6.4 milli- meters), and 3 inches to 6 inches in depth (7.6 to 15 centimeters). Nest surfaces should be dark in color, with anecdotal evidence suggesting that blue and black colors are most attractive.
Nest dimensions should be configured to promote bee health and maximize female production, as well as facilitate ease of orientation for foragers return- ing to the nest. Larger (¼ inch, 6.4 millimeters) and deeper (4 to 6 inches, 100 to 150 millimeters) holes should be used when possible as they encourage larger, healthier brood as well as a higher propor- tion of female offspring. Inter-hole distances of 3/8 inch (9.5 millimeters), or even higher, will result in easier orientation for female bees that are returning to the nest from foraging trips. Bees that can easily find their nest hole will complete nests more quickly, and are less likely to enter the wrong nest holes
Figure 7.14 Grooved wooden boards used to be a popular nest option. However boards warp and crack over time and the spaces between boards provide entry points for parasites.
Figure 7.15 Under optimal conditions, these Styrofoam nest blocks are rapidly filled. The open nest holes are the result of second-generation bees which have recently emerged. See sidebar, Second-Generation Bees (page 81).
where they could become contaminated with disease spores. Commercially available Styrofoam nests tend to have very high hole densities. Similarly, nests with painted, raised or textured orientation patterns, and irregular surfaces (such as wood), all result in easier orientation for returning foragers.
Currently no single nest type is free of problems, and there is much room for experimentation. It is likely that an optimal nest for small producers may be a hybrid of some of the systems listed above— a solid block with removable inserts for example (see Appendix E, page 134). Such a system would no doubt greatly increase labor, but would probably result in a higher percentage of healthy female bees. For more information on the benefits and drawbacks of loose-cell verses solid-board nests, see Appendix F, page 138.