Idaho’s Treasure Valley is an irrigated high desert, making
it a diverse agricultural region producing crops for humans and animals. Many
of these crops require pollination, so there are plenty of managed bee colonies
in the area. Most of the crops are pollinated by the honey bee, Apis mellifera, that American beekeepers
house in familiar Langstroth bee hives. However, one crop, alfalfa, an important
animal food crop and the principal hay crop for dairy cattle, is largely
pollinated by another bee species. When alfalfa is grown to produce seed, the alfalfa
leafcutting bee, Megachile rotundaata,
may be brought into the fields to ensure adequate pollination for the
production of seed. The alfalfa plant, a member of the legume family, produces
ample amounts of nectar and pollen and is attractive to honey bees. However,
honey bees don’t like foraging alfalfa due to the physical structure of alfalfa
flowers. When a honey bee forager attempts to access alfalfa nectar or pollen,
the flower slaps the bee’s face with considerable mechanical force.
The reluctance of honey bees to forage alfalfa makes the
alfalfa leafcutting bee a favorable choice especially for alfalfa seed
production where ample insect visits are necessary for pollination. Alfalfa
leafcutting bees are not social bees like honey bees; they are solitary. Honey
bees live in large colonies housed in wooden hives. Gregarious alfalfa
leafcutting bees are solitary bees; large numbers of beekeeper-managed solitary
bees live in close proximity in tubes bored into wood or plastic boards. The
alfalfa leafcutting bee nesting tubes shown in today’s photo are cut into
blocks of polystyrene. Adult leafcutting bees are emerging from some blocks.
Other blocks with empty tubes are available for leafcutting bees to occupy.
After mating, a female leafcutting bee cuts leaf material and carries it to an
available tube where she deposits an egg along with pollen and nectar to feed
the developing offspring. A large amount of chewed leaf matter is visible under
the leafcutting bee hive blocks.
--Richard