Being able to place bees in the fields when the alfalfa is in bloom
is one major advantage of incubation after refrigerated, overwinter
storage.
- Incubation calendar
- Incubation of bee nests after
non-refrigerated storage
- Use of lights over pan traps
in incubation room
- Manipulation of incubator
temperatures to delay emergence
- Use of dichlorvos (Vapona pest
strips)
- Further Information
I. Incubation of bee
cells at 85°F after refrigerated storage will result in the
following developmental sequence:
(see an updated incubation calendar at the IPS
web site)
Day 1.
Incubation begins. Bees are in a worm-like larval form, totally white in
color.
Day 9.
Bee larvae begin to change into white pupae.
Day 10.
Pteromalus and Tetrastichus parasites begin emerging from
parasitized bee larvae. They appear as tiny black wasps. (Eves
et al. 1980)
Day 14.
Monodontomerus parasites begin emerging from parasitized bee
larvae. They appear as tiny black wasps. (Eves
et al. 1980)
Day 15.
Bee pupae are totally black in color.
Day 17.
First adult males are fully formed in the cells.
Day 18.
Males begin emerging. All cells still in nesting material (boards, etc.)
should be placed in the field.
Day 20.
The first female bees emerge.
Day 22.
In loose cell management, incubation trays should be taken to the field
and the lids removed so the bees can escape; 30 to 50 percent of the
females should have emerged by this time.
Day 28.
Most bees should have emerged.
Advantages of Controlled Incubation:
- Bee emergence can be accurately predicted if bees have been in
cold storage for about 250 days.
- Most incubated bees emerge within 2 weeks after being placed in
field shelters.
- Many bee enemies can be collected and destroyed during the
incubation and phase out process.
Disadvantages:
- Bee cells require daily attention during the incubation period.
- The cost of the incubator and its operation raises operating
expenses.
- Controls may malfunction resulting in an excessively high
temperature that can kill bees.
- Loose cells in incubation trays must be specially protected from
parasites during the incubation process.
Pesticides may harm the bees.
II. Incubation of bee nests at 85°F
after non-refrigerated storage.
Advantages:
- Bee emergence will begin in 19 days or sooner, depending on
pre-incubation storage temperatures.
- All advantages listed for incubation after refrigerated storage
with the exception that emergence will not be as uniform.
Disadvantages:
- All disadvantages listed for incubation after refrigerated
storage.
- Nest-destroying enemies multiply any time storage temperatures
exceed 40°F. Consequently, more nest destroyers may be present
during incubation, which is a favorable period for feeding, growth
and reproduction of these bee enemies.
III. Manipulation of incubator
room temperatures to delay bee emergence during period of cold, wet
weather that delays alfalfa bloom in the spring.
Procedures:
- During the normal 19-day incubation period, at
85°F and 50 to 70 percent relative humidity, temperatures may be
lowered and maintained as low as 79°F if
necessary to slow bee development. Use degree day
accumulations to estimate how much development has taken
place.
- After day 14 of the normal incubation period, bee
emergence can be delayed as much as an additional two weeks by holding the
temperature between the narrow limits of 50 and 59°F). These
temperatures stop immature bees from developing. Development
continues when temperatures are raised above 60°F, but typically
growers continue development at 85°F. Use degree day
accumulations to estimate how much development has taken
place, and how long to emergence.
Advantages:
- Bee development can be delayed so emergence coincides
with the availability of alfalfa bloom and/or favorable weather.
Disadvantages:
- During the last half of the incubation period, temperatures lower
than 60- 65°F may cause some bee mortality.
- During this same period, temperatures above 67°F, especially
above 70°F, will permit some bees to emerge within the incubation
room. These bees will die from starvation.
IV. Use of lights over oil or water pan
traps in incubation room.
Advantages:
- A combination of incandescent and fluorescent "black
lights" attracts many nest-destroying insects and parasites
emerging during incubation. Many of these emerge from nests earlier
than bees and are easily destroyed in oil or water-filled pans
positioned directly under the lights.
- The use of water pans will help maintain relative humidity between
the required 50 and 70 percent during incubation.
Disadvantages:
- Extra labor is necessary for daily maintenance.
- Light fixtures must be purchased and installed.
- The light-proof room must have temperature and relative humidity
controls.
- Leafcutting bees are also attracted to these lights. Early
emergence or unexpected delay in placing bees into field shelters
can lead to some bee mortality.
V. Use of dichlorvos (Vapona pest
strips) in closed storage rooms.
Advantages:
- This pest strip kills many nest-destroying insects quickly.
Dichlorvos can be used in closed storage and incubation rooms after
bees have finished emerging in the spring to eliminate most
remaining pests.
Disadvantages:
- This pesticide can kill bees in closed storage rooms and
incubators, especially when humidity is <70% . (read
Wayne Goerzen's
research report on this subject)
- These strips are not legally registered for use in rooms
containing alfalfa leafcutting bees.
Further Information
IPS
incubation calendar
Degree day accumulations
Eves, J.D., D.F. Mayer, and C.A. Johansen 1980. Parasites, Predators
and Nest Destroyers of the alfalfa leafcutting bee, Megachile rotundata.
Western Regional Extension Publication (WREP) 32. (Contact your county
extension office to order a copy).
Stephen, W.P. and C.E. Osgood. 1965. The induction of emergence in the
leaf-cutter bee Megachile rotundata, an important pollinator of alfalfa.
J. Econ. Entomol. 58: 284-286.
Whitfield, G.H. and K.W. Richards. 1987. Postdiapause development and
adult emergence of Pteromalus venustus Walker (Hymenoptera: Pteromalidae)
during alfalfa leafcutter bee incubation.
Richards, K.W. and G.H. Whitfield. 1988. Emergence and survival
of leafcutter bees, Megachile rotundata, held at constant
incubation temperatures (Hymenoptera: Megachilidae).
Peterson,S.S.,
C.R. Baird, and R.M. Bitner. 1991. Variation in
weight and postdiapause development among groups of alfalfa leafcutting
bees, Megachile rotundata (F.), reared in different locations. Bee
Science 1:230-236.
Kemp, W.P. and J. Bosch. 2000. Development and emergence of the
alfalfa pollinator Megachile rotundata (Hymenoptera: Megachilidae).
Ann. Entomol. Soc. Am. 93:904-911.
If you have comments, corrections, or additions to the information provided
in this document, contact Karen.