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Environmental Factors Influencing Spring Emergence of the Blue Orchard Bee in Virginia

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Title: Environmental Factors Influencing Spring Emergence of the Blue Orchard Bee in Virginia


1
Environmental Factors Influencing Spring
Emergence of the Blue Orchard Bee in Virginia
Mark Kraemer and Françoise Favi, Virginia State
University, Agricultural Research Station, P.O.
Box 9061, Petersburg, VA 23806
Fig. 10.
Introduction Blue Orchard Bee, Osmia
lignaria Say, a mason bee native to temperate
North America, is an excellent spring pollinator
of tree fruits and nuts. The western
subspecies, Osmia lignaria propinqua Cresson, has
been used in apple, cherry, peach, plum,and
almond orchards in the western U.S. (Bosch and
Kemp 2001). The eastern subspecies, Osmia
lignaria lignaria Say, is currently being studied
for use in eastern orchards as an alternative or
suppplement to the honey bee Apis mellifera L.
(Kraemer and Favi 2005). The native bee is a
more efficient pollinator, active in cloudy, cool
weather, has a greater focus on the target crop
(limited foraging range), and is not affected by
many of the problems afflicting honey bees. Osmia
lignaria should be especially valuable for
organic production because pesticides are not
needed to control varroa mites, hive beetles and
other pests that affect honey bees.
Osmia liganria is univoltine and active for about
6-weeks in the early spring. Although emergence
can best be contolled with winter storage under
controlled conditions, it is less costly for
limited-resource producers to utilize the natural
environmental for overwintering. Our objective
was to determine the environmental factors
responsible for emergence. Accumulated degree
days were unlikely to be responsible because
winter diapause is in the adult stage and
emergence may occur in mid-winter under room
temperatures.
Results and Discussion Males emerged before
females (Figs. 1-6). Initial male emergence was
associated with overnight lows above 9C. Bee
emergence appear less sensitive to periods of
warm overnight temperature earlier in the season.
Male emergence began after 1 night of warm
temperature (gt9C) in 2005 (March 28th), 2 nights
of warm temperatures in 2003 (March 18th), and 3
nights in 2004 (March 6th) (Figs. 1-3). Average
AM temperatures (midnight to noon) are related to
minimum overnight lows but are not as easy to
calculate for growers and do not appear as
closely correlated as overnight lows (Charts
4-6). However, statistical analysis has not yet
been done. Rapid changes in
atmospheric pressure also appears to have an
effect on bee emergence (Figs. 7-9). In 2005, a
rapid drop in barometric pressure during the
afternoons of March 28th and April 2nd to very
low levels (29.2 mm Hg) was associated with poor
emergence the following day (Chart 9).
Initial bee emergence was not correlated with
degree days (Fig 10). The warmest winter (2005)
had the latest emergence. Adult mortality, the
percentage of intact cocoons without emergence,
was unusually high in 2005 at 29, compared with
12 in 2004 and 10 in 2003. This may be related
to the unusally warm 2005 winter. In addtion, a
cool spring followed the unusually warm winter
and bee emergence was delayed (Figs. 1-3),
possibly contributing to the higher mortality.
Horticulturalists use a Chill Index (Fig
11) to match fruit tree cultivars to local winter
climates (Anderson et al. 1986). Trees that
experience a winter with less than the required
number of chill hours have poor flowering over
extended periods. Bee populations may be
similarly adapted to chill periods. The warm
2004-5 winter had less than 1800 chill hours,
perhaps less than required for optimal bee
survival. Emergence appeared to be slower after
night minimum temperatures rose above the 9C
threshold. Kemp et al. (2004) in controlled
studies of the western subspecies (Utah) reported
that adult diapause requires a minimum of
approximately 3 months of wintering at 4C to be
completed. For comparison, our winters ranged
from 60 to 71 days at or below 4C (total cold
hours/24 hours). Despite major weather
differences between years, the emergence of
female bees was well coordinated with the
observed flowering of local apple and cherry
trees. The wide distribution of this bee in
North America provides an opportunity to utilize
local populations that are adapted to the
prevailing climatic conditions.
Fig. 11.
Materials and Methods Environmental
conditions were monitored near a local population
of Blue Orchard Bees over a three year period as
part of a larger project (Kraemer and Favi 2005).
Artificial nest boxes were provided in a
riparian forest coridor near the fall line of the
Appomatox River, Virginia. Bee cocoons were
collected in October/November and placed in
gelatin capsules. These capsules were placed in
glass jars and kept overwinter in wooden shelter
boxes attached to trees in the study area.
Emergence was checked daily during the spring and
male and female emergence recorded. Temperature
and humidty were recorded with data loggers
(Onset Computer Corportation, Bourne, MA) placed
within 10 meters of the overwintering shelter
boxes. Average 12-hour temperatures were
determined for AM and PM. Barometric pressure
was recorded in inches of Mercury (Vantage Pro
weather station Davis Instruments, Hayward, CA).
Degree days were calculated on a base of 4 C
and started on January 1st. A simple chill
index was determined by adding the number of
hours during which temperatures were below 6C,
starting from September 21st.
References Anderson, J.L., E.A. Richardson, and
C.D. Kesner. 1986. Validation of chill unit and
flower bud phenology models for Montmorency
sour cherry. Acta Hort. 18471-86. Bosch, J.,
and W. P. Kemp. 2001. How to Manage the Blue
Orchard Bee. Handbook Series, Book 5, Sustainable
Agriculture Network. Nat. Agri. Lib., Beltsville.
Kemp, W. P., J. Bosch, and B. Dennis. 2004.
Oxygen consumption during the life cycles of the
prepupa-wintering bee, Megachile rotundata and
the adult-wintering bee Osmia lignaria
(Hymenoptera Megachilidae). Ann. Entomol. Soc.
Am. 97 161-170. Kraemer, M., and Favi. 2005.
Flower phenology and pollen choice of Osmia
lignaria (Hymenoptera Megachilidae) in central
Virginia. Environ. Entomol. (in press).
2003
2004
2005
Fig. 2
Fig. 3
Fig. 1
Fig. 4
Fig. 6
Fig. 5
Fig. 8
Fig. 7
Fig. 9
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