Leafcutter bees are the bee of choice when it comes to pollinating alfalfa. They are aboveground nesters and good pollinators, which favour alfalfa nectar. According to Bob Mennie, production manager of Mennie Bee Farms Inc., near Parkside, Sask., leafcutter bees are “easy to handle and tend to stay close to where the shelters are.”
Managing the bees
Bees are put out into the field when the alfalfa has five to 10 per cent bloom, to ensure that the bees have food. This usually happens around July 1. Bees released too early will stray from their shelters to search for food.
The bees moved to the field are about 75 to 90 per cent hatched. They will live out their life cycle, then the farmer will retrieve the next generation of bees at the end of the season. In general, there will be one and a half to two times as many new bees, in the larval form.
Bees in the field are fairly self-sufficient. Checking the shelters weekly for wildlife or wind problems is a good management practice. Toward the end of the season, Mennie says, “Getting the nesting block out of the field and into the safety of the processing building as soon as the bees have finished working is a good idea.”
Crop insurance requires 20,000 bees per acre; this is the benchmark for good alfalfa pollination. Flying fewer bees per acre tends to increase bee production, but more bees per acre means more cross-pollination and therefore better seed production.
The number of bee shelters per field varies depending on each farmer’s individual setup. Smaller plastic shelters may be placed at rates of about one shelter per 2.5 acres, as on the farm of alfalfa seed producer Randy Toman of Guernsey, Sask. The Mennies use large shelters of their own design — one shelter can cover 15 to 25 acres. Fewer shelters means the Mennies have a lower cost per acre for shelters as well as increased efficiency.
The number of nesting blocks per shelter depends on the size of the shelter.
The plastic shelters are lightweight and can be stacked inside each other as one would stack chairs. Metal and wood shelters are more expensive, but may last longer than the plastic ones. Setting up shelters is fairly straightforward, requiring a couple of people and either a trailer or a tractor with a front end loader to move the shelters to the field.
“Efficiency is the name of the game in the bee business,” Mennie says. Labour is expensive and difficult to find.
- From the Country Guide website: Keeping bees
The two popular types of nesting material available are wood or polystyrene blocks. Polystyrene blocks are cheaper, lighter, reasonably simple to treat for disease or sample for sale, and are easier to work with, making them the current industry standard. However, they are more prone to damage than wood blocks.
Of the bees put out in the field, about 35 per cent are females. In a typical polystyrene nesting block, there are 3,540 tunnels. On the Mennie farm, there are approximately five nesting blocks per acre, and each female has about two to 2.5 tunnels to fill over the season. At the end of the season, these tunnels are filled with the cocoons built from the alfalfa leaf material the bees collect.
Pest and disease control
Two species of small, parasitic wasps target leafcutter bees. While there are insecticides that can be used in the incubators to control these pests before the bees hatch, Randy Toman, a farmer from Guernsey, Sask., says there is no chemical control for parasites in the incubator after hatching. The best defence against parasites in the field is good management: proper assembly and installation of nesting blocks and replacing damaged blocks. “There’s a backing that goes on the back of the nests that prevents parasites from getting in,” Toman says. “It’s very important to have your nests put together properly before you take them out to the field. That’s a major control.”
Disease-wise, moisture means mould. The alfalfa leaf material collected by the bees contains millions of naturally-occurring mould spores, so the faster the cocoons are dried, the less mould there will be. Mould affects bees’ overall health and virility.
Sterilization is the simplest way to control mould. The fungal chalkbrood disease can be even more devastating than mould to bee populations. The simplest way to control this disease is to avoid purchasing bees of poorer quality or from areas known to have disease, and to thoroughly clean any used equipment purchased so the chalkbrood spores are not brought onto the farm.
The sterilizing agent paraformaldehyde is a gas that kills mould spores. It can be used on the collected cocoons at the start of the season as well as on the used nesting material and equipment, including harvest equipment and the incubators used to hatch the bees. A bleach solution can also be used. Wood nesting blocks can be heat treated.
Once the nests are brought in from the field, they should be dehumidified by blowing fans over the nests in preparation for harvest of the bees. At this point, they are kept at about 18 to 21 C to ensure that the larvae have had enough time to spin their cocoons inside the leaf cocoons. The Mennies allow at least two weeks for this to occur, after which they harvest the bee larvae and store them in cardboard boxes at about 4 C and as low a humidity as possible. “[The larvae] can’t get too cold or they’ll freeze, and if they get too warm they’ll start to incubate,” says Toman.
Come spring, the larvae are incubated for 22 to 24 days. Incubation typically starts in the first week of June. In the incubators, the humidity is kept relatively high as the bees develop and the temperature is kept around 30 C. At the end of this period, all of the males and about 80 per cent of the females have hatched, and the incubation trays are taken to the field and put into the shelters. When the lids are taken off, the hatched bees fly out.
Selling excess bees
Farmers who maintain their own bee populations keep enough bees for pollination in the coming year and sell the excess. While most bees are sold into the U.S., other markets include the hybrid canola market and Eastern Canada’s blueberry industry. “There is some red tape exporting [bees] to the United States,” says Mennie.
Bees are sold by the gallon — about 10,000 bees. While price per gallon varies, last year’s top price was about $100/gallon.
Farmers interested in growing alfalfa for seed but not interested in getting into leafcutter bee production can look into custom pollination. Information is available through the Alfalfa Seed Commission (Alberta), the Manitoba Forage Seed Association, or the Saskatchewan Leafcutters Association.