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Alfalfa Leafcutter Bees

Alfalfa leafcutter bees (Megachile Rotundata) were first imported to Canada (into Southern Alberta) by G.A. Hobbs in 1962. From a small beginning they have expanded into a much larger area covering approximately 36,000 acres in Saskatchewan, 13,500 acres in central and southern Manitoba and 24,000 acres in the Peace River, Brooks and Lethbridge areas of Alberta in 2011. At one point these bees covered more than 200,000 acres in Western Canada

Most of the leafcutter bees are produced on alfalfa in the three provinces; the acres involved are small compared to other crops.

Alfalfa flowers won’t set seed unless they’re cross-pollinated and tripped. Leafcutter bees are used in alfalfa as they tend not to move far from where they’re released unless they’re short of food.

Leafcutter bee lives

The life of a leafcutter bee is short. Males live two to four weeks; females live six to 12 weeks.

The bees are stored as larvae in cocoons, and take 18 to 24 days to change into adult bees.

The cells are placed into incubation trays and placed in to an incubation chamber for hatching. This room is kept at 30 C; steps are taken to eliminate a parasitic wasp that hatches during the incubation period. At approximately 15 to 18 days the males start to emerge from the cocoons. At about 19 to 21 days, the first females emerge. Then, the trays are taken to the field where they are opened up and placed in the huts. The later females hatch in the heat of early summer.

The release of bees into the field is timed for when the alfalfa reaches ten per cent bloom. The huts are placed with a range of two to five acres per hut, depending on hut size, bee numbers per acre, and whether the land is irrigated.

The female bees cut small sections of leaf or petals from crops or weeds to build bee cells in the nesting material supplied. When the bee has formed the base and sides of the cell, she collects pollen and nectar to provision the cell, and then lays an egg on top of the nectar. She uses additional leaves to seal the cell.

The male bees pollinate the flowers as they’re feeding themselves. Their only other task is breeding females — not building cells.

Once a cell is complete, the bee starts building the next cell. This continues throughout its life.

At the end of the season, or when the cells are over 80 per cent full, the nest blocks are removed from the huts in the field.

Meanwhile, the eggs inside each cell have hatched. These larvae eat the nectar and pollen, grow and spin cocoons. The cells are placed in a temperature controlled room at 15 C long enough to ensure the larvae are fully developed before the temperature is reduced. Once the cocoons are fully dried, they are removed from the nest block and processed for use on the farm next season or packaged for sale off the farm.

Leafcutter bees usually reproduce 1.5 to two times the number of bees released into a field. The extra bees harvested during the winter are usually sold off the farm.

Bee economics

Over the last ten years, cocoon prices have ranged from $5 to $110 per gallon (10,000 healthy cocoons). Usually, two to five gallons per acre are used in alfalfa fields. This allows good pollination and reasonable reproduction for the bees.

The value of seed and bees produced are significant for the farms involved and contribute greatly to Western Canadian agriculture with their value to pollinating other crops, especially hybrid canola in Southern Alberta. In 2011 the market value of alfalfa seed and bees at the farm gate was approximately $20 million in Saskatchewan alone. †

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