Agriculture Reference
In-Depth Information
Insect pollinators are valuable and limited resources (Delaplane and
Mayer 2000). Currently, farmers manage only 11 of the 20 000 to 30 000
bee species worldwide (Parker et al., 1987), with the European honey-bee
(
Apis mellifera
) being by far the most important species. Depending on
only a few pollinator species belonging to the Apis genus has been shown
to be risky.
Apis
-speciic parasites and pathogens have lead to massive
declines in honey bee numbers. Biotic stress accompanied with climate
change may cause further population declines and lead farmers and re-
searchers to look for alternative pollinators. Well-known pollinators to
replace honey bees might include the alfalfa leaf-cutter bee (
Megachile
rotundata
) and alkali bee (
Nomia melanderi
) in alfalfa pollination (Cane
2002), mason bees (
Osmia
spp.) for pollination of orchards (Bosch and
Kemp, 2002; Maccagnani et al., 2003) and bumblebees (
Bombus
spp.) for
pollination of crops requiring buzz pollination (Velthuis and van Doorn,
2006). Stingless bees are particularly important pollinators of tropical
plants, visiting approximately 90 crop species (Heard, 1999). Some habits
of stingless bees resemble those of honey-bees, including their preference
for a wide range of crop species, making them attractive for commercial
management. Pollinator limitation (lack of or reduced availability of polli-
nators) and pollen limitation (insufficient number or quality of conspecific
pollen grains to fertilize all available ovules) both reduce seed and fruit
production in plants. Some crop plants are more vulnerable to reductions
in pollinator availability than others. (Ghazoul, 2005) defined vulnerable
plant species as:
• having a self-incompatible breeding system, which makes them de-
pendent on pollinator visitation for seed production;
• being pollinator-limited rather than resource-limited plants, as is the
case for most intensively grown crop plants, which are fertilized; and
• being dependent on one or a few pollinator species, which makes
them particularly sensitive to decreases in the abundance of these
pollinators.
Semi-natural habitats provide important resources for wild pollinators
such as alternative sources of nectar and pollen, and nesting and breeding
sites. Especially in the United States, many of these intensively cultivated
agricultural areas are completely dependent on imported colonies of man-
aged honey-bees to sustain their pollination. The status of managed honey-
bees is easier to monitor than that of wild pollinators. For example, bee
