Early season bumbles

It was only 11 degrees this afternoon, and breezy, but fine with blue skies. The patch of tree lucerne I pass on the way home was thick with flowers so I stopped to see who was foraging. Some queen bumble bees were out, gathering supplies to start their colonies.

Canterbury blackcurrant growers estimate that pollination is a limiting factor to yields in one year out of three. Black currants don’t pollinate by wind, unfortunately, because the pollen is quite sticky.  Insects do the job, when the weather is cooperative.

This article talks about bumble bee pollination of black currants, and what growers can do to encourage wild populations of bumble bees, specifically Bombus terrestris, the “buff tailed bumblebee,” or “short tongued bumble bee,” because this is the species that is out early enough to be a factor in black currant pollination.  Native solitary bees ramp up later in the summer.

There are Four Pillars of Bumble Bee Joy to consider:

1. Food for queens emerging in late winter
2. Nesting holes for colonies in late winter
3. Continuous flower-food sources after black currant bloom to support colonies the rest of the year
4. Don’t kill them with insecticides

The only bumblebee of the colony that makes it through winter is the queen, hibernating in a hole in the ground.  In the late winter, as ground temperatures start to rise, she emerges hungry and energetic, needing to build a colony from scratch all by herself.  She needs fuel, and a place to make a nest.  Late winter blossoms are in pretty short supply, so the First Pillar of Bumblebee Joy is to make sure you have flowering plants at this lean time.  Tree lucerne is a good fit for this, and is very attractive to bumblebees.  Other plants blooming right now are Rosemary, Pussy willow (Salix aegyptica), Grevilleas, Banksias, Wattles.  I’ve noticed the gorse is flowering now, but we shouldn’t probably plant any more of that weed.

The Second Pillar of Bumblebee Joy is good nesting sites.  In the wild, queens look for abandoned mouse burrows or cavities in/under rotten logs.  They need material they can fluff up to make a nest.  Man-made boxes can be set out, but they can sometimes be discouraging for a grower because the occupancy rate is a bit hit-or-miss.  Sam Read, entomologist at Plant and Food Lincoln, talks about work they’ve done with bumblebee nest boxes in the Marlborough grape region.  Sometimes nearly every box had a colony, and at other sites, almost none were occupied, even on farms where growers were quite interested in conserving bees.  Nest boxes are also attractive homes for mice, so they’re not a “set and forget” solution.  Late winter (August) is the time frame to make sure they’re cleaned out and provisioned with fresh insulation (pink batts work well) for the emerging queens.

The Third Pillar of Bumblebee Joy is to make sure there is food for them after black currants are finished blooming.  Some black currant growers use herbaceous grazing mixes that flower throughout the summer, like mixes that include clover.  Yes, there are trade offs between a dense canopy under the bushes which becomes impossible to mow after rows close, so perhaps the headlands and drive rows are a better compromise.

The Fourth Pillar of Bumblebee Joy is really about preservation—avoid broad spectrum insecticides that will do them harm.  Karate is in this bucket, which is why we stress that it’s a one-year-only rescue treatment for blocks where clearwing populations have become too high to be managed with pheromone ties.  Lorsban is off the industry approved list for this season—scale can be managed with softer approaches like oil and Ovation.

I’m looking forward wandering around and noting what the bees are interested in eating, and where those nest sites might be.

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