Agriculture Reference
In-Depth Information
20.3
TEMPERATURE SENSITIVITY OF CROP POLLINATORS
Bees are the most important pollinators worldwide (Kearns et al., 1998)
and like other insects, they are ectothermic, requiring elevated body tem-
peratures for flying. The thermal properties of their environments de-
termine the extent of their activity (Willmer and Stone, 2004). The high
surface-to-volume ratio of small bees leads to rapid absorption of heat at
high ambient temperatures and rapid cooling at low ambient temperatures.
All bees above a body mass of between 35 and 50 mg are capable of
endothermic heating, that is, internal heat generation (Bishop and Arm-
bruster, 1999; Stone and Willmer, 1989; Stone, 1993). Examples of bee
pollinators with a body weight above 35 mg are found in the genera
Apis,
Bombus, Xylocopa
and
Megachile
. Examples of small bee pollinators are
found in the family Halictidae, including the genus
Lasioglossum
. All of
these groups are important in crop pollination.
In addition to endothermy, many bees are also able to control the tem-
peratures in their flight muscles before, during and after flight by physi-
ological and behavioral means (Willmer and Stone, 1997). Examples of
behavioral strategies for thermal regulation include long periods of bask-
ing in the sun to warm up and shade seeking or nest returning to cool down
(Willmer and Stone, 2004). With respect to the potential effects of future
global warming, pollinator behavioral responses to avoid extreme temper-
atures have the potential to significantly reduce pollination services (Cor-
bet et al.,
1993). The natural distribution of the European dark bee (
Apis
mellifera
) is found in a region where average July temperatures ranges
from 15-20°C, which may represent their thermal tolerance. The Eastern
honey-bee (
Apis cerana
) is native to parts of Asia. The giant honey-bee
(
Apis dorsata
) lives only at tropical and adjacent latitudes in Asia and oc-
curs less widely than the Eastern honey bee (
Apis cerana
), but can live at
higher altitudes. The dwarf honey-bee (
Apis florea)
) is more restricted than
that of the larger
A. dorsata
and
A. cerana
. It is mainly found in Asia.
The effect of climate change on pollinators depends upon their ther-
mal tolerance and plasticity to temperature changes. Our goal was to ob-
tain thermal tolerance data for the most important pollinators worldwide.
However, a literature review indicates that this information is missing for
most species.
