Gardens for Bumblebees

My good colleague, Maria Kasstan spoke to the Toronto Beekeepers' Cooperative last evening. She had just returned from attending the annual pollination symposium in Guelph. The City of Guelph, Ontario, it turns out, has a very active, city-wide pollinator awareness program. A rallying point for all of this activity is Pollination Guelph, sponsor of the symposium.

Now Guelph has for many decades been home to the Ontario Agricultural College and Guelph University. Lots of bee people work there, with plenty of interest in pollination biology. But that doesn't quite explain it all. An enthusiasm for pollination and pollinator-friendly gardens in Guelph seems to extend through the city council and many branches of city government as well.

Maria kindly gave us a capsule account of what she learned. Her talk was fascinating, especially for someone interested in bumblebees.

Bumblebees, in particular, were mentioned during the symposium, including news of the recent promising sighting of the Rusty-patched Bumblebee in Ontario's Pinery Provincial Park. Also discussed was the relationship between arctic bumblebees on Ellesmere Island and the flowers they visit. Apparently the corolla of the flower serves as a parabolic reflector to concentrate the sun's warming rays. So in that chilly climate, bumblebees visit the flower to keep warm, effecting pollination at the same time.

But the big topic of the day was how to develop gardens that serve as habitat not only for bumblebees, but for all insect pollinators. The City of Guelph, under its Healthy Landscapes program publishes lists of pollinator friendly plants to include in the garden. They cover bee, butterfly and hummingbird plants, sun and shade tolerant native plants, as well as trees and shrubs that provide pollinator resources.

The guidelines for pollinator gardens include:

• plant plenty of nectar and pollen rich flowers
• provide food sources (host plants) and overwintering places for eggs and pupae
• provide water
• avoid using pesticides and herbicides
• provide sites and materials for nesting and overwintering
• reduce your area of lawn grass

Because of monoculture and pesticide use, agricultural areas provide no comfort for bumblebees. So what we do in our cities and in our own gardens may be the best hope for bumblebee conservation.

[Photo by Jina Lee, CC License]

The Fly and the Bumblebee: Not a Love Story

The Toronto Entomologists' Association invites some great speakers. Yesterday we were treated to nine grad student presentations on topics ranging from the identification of syrphid fly pollinators to the diversity of aquatic invertebrates. Especially, it seemed, there's an awful lot of fly research going on in southern Ontario.

Most interesting to me was a paper given by Joel Gibson of Carleton University on the fly family Conopidae, some members of which are parasitic on bumblebees. Actually the technical term for these Thick-headed Flies is parasitoids. A parasitoid is any parasite that spends an extended time in the body of its host and is so large that as it grows it ultimately kills that host. Parasitoids, you could say, are parasites that are rather more like predators than like ordinary parasites.

Right: A conopid fly of the genus Physocephala, known to be parasitoids of bumblebees. Note that unlike most flies, the antennae are quite long, making it a more effective wasp mimic.

Adult Thick-headed Flies are rather elegant-looking creatures, with a slim, wasp-like body and black-and-yellow waspish colors. They visit flowers where they feed on nectar.

And it is presumably around flowers where they encounter unsuspecting bumblebees. The fly is said to be able to alight on the flying bumblebee and deposit an egg into its body. When the fly larva hatches, it burrows deep into its host and begins to feed on the bumblebee's tissues.

In some areas, we were told, 40% to 50% of the bumblebees are carrying conopid larval parasitoids. The infected bees become feeble and unable to fly. They may be found walking on the ground, their abdomens swollen by the mature fly larva that has consumed most of their internal organs. Eventually the bee dies and the Thick-headed Fly larva pupates inside.

Thick-headed Fly parasitoids are yet another pressure on bumblebee populations. The fly is, no-doubt, something that bumblebees have evolved to cope with over time. But when combined with habitat destruction and widespread pesticide use, this highly effective parasitoid is just one more potentially dangerous stressor.

[Photo by James Lindsey, CC license]

Bumblebees and Climate Change

Bumblebees can now be spotted all year round in southern England (Read more here).

Yes, British Winters are still cold, but not as cold apparently, as they used to be. Bumblebees are hardy anyway, and can continue to fly in search of food at colder temperatures than most other pollinators. Besides, in British gardens there are apparently some cultivated plants that bloom during the Winter months, so the bee food supply is continuous.

Right: The Buff-tailed Bumblebee, a British species seen in very early Spring.

Bumblebees in temperate climates usually escape winter as part of their annual colony life cycle. Normally it is only the fertilized queen that overwinters. In the Fall, she chooses a sheltered spot, often in a shallow burrow in the soil. There she waits until winter has passed and Spring flowers promise a fresh supply of nectar and pollen.

The queen begins a new colony first by finding an abandoned mouse nest or other suitable cavity, often underground. She gathers nectar and pollen to nourish the larvae that develop from the eggs she lays. When her first brood of worker bees emerge as adults, they take over the job of gathering food, leaving the queen to the tasks of laying eggs and maintaining order in the colony.

By mid- to late-Summer, the bumblebee colony starts to produce sexually active males and queens. When these new queens have mated, they are the ones who normally overwinter and begin the next generation. The old queen and the remaining workers and drones usually die when they can no longer find enough food and the first heavy frosts overtake them.

These observations of Winter-active bumblebees in southern England raise some intriguing questions. Are they mated queens that just don't bother to hibernate? Or are they workers and males left over from the previous summer who can still find enough food to survive? If the latter, do last year's workers and males become competitors with the new queens for scarce Spring food resources?

Dave Goulson's observations suggest that mated queens of Bombus terrestris in southern England just go ahead and found a new nest, not bothering to hibernate first. But if they were to start simply laying eggs in their maternal colony, this would seem to put the species well on the way towards continuous, immortal colonies, like those of honey bees.

As with all of the many changes that have occurred in Earth's environment during past millenia, those bumblebees that can adapt gracefully will survive and prosper. Those that cannot adapt will become just another chapter in bumblebee history.

[Photo of B. terrestris from the Wikimedia Commons, CC License]

A Hopeful Sign?

The Rusty-patched Bumblebee (RPB) seems to have been a casualty. The Xerces Society, a not-for-profit organization that specializes in the protection of invertebrate animals and their habitat, has identified the Rusty-patched as one of four North American bumblebees that have experienced serious decline in the last 50 years. This RPB is one of the prime examples of why bumblebees need our help.

Right: Color pattern diagrams for workers of the Rusty-patched Bumblebee (Bombus affinis)

The RPB was formerly widely distributed in eastern and central North America. It is represented by specimens in historical insect collections from southern Ontario and Quebec in Canada, and all the way from Minnesota across to Maine in the northern U. S. It also occurred in a wide swath down the eastern part of the continent, as far south as Georgia. Today it has disappeared almost entirely from that entire broad range.

A recent study by bee researchers, Sheila Colla and Laurence Packer has provided quantitative evidence for the decline of the RPB. They collected intensively in two locations where RPB was formerly found over a period of three years. They were completely unable to locate the species in its former haunts. Broader collecting throughout most of the former range turned up only one remaining stand of the species in southern Ontario.

Fortunately, last year, the missing species was also sighted by biologist Liz Day in Indiana. This has to be a hopeful sign.

You can help. The Xerces Society would like everyone to be on the watch for the Rusty-patched Bumblebee. If you want to learn how to spot, they have information and even an identification guide on their site. You can see more photos of the species HERE, HERE and HERE.

There may still be hope for the Rusty-patched Bumblebee. Let's try and give all bumblebees a better chance by protecting their habitat and planting more bee-friendly flowers.

Maybe one day we'll see the RPB flashing its brown patch among the blossoms in our gardens once again.

Bee Degree Days

In addition to avoiding each other, emerging bumblebee queens need to be out and flying around when their favorite early food plants are blooming. Too early and it's too cool, with no nectar or pollen. Too late, and the blooming period is over, the preferred food all gone.

How do they do it? How do they figure out when to emerge, especially underground, or buried in a rotten log, where the sun doesn't shine to let them know the days are getting longer?

Bumblebees can apparently tell when to emerge the same way biologists can predict the dates for Spring plants to flower - they use growing degree days.

Biologists have found that Spring flowers bloom after their buds have received enough heat. During the depths of winter, no bud development happens at all. But in late Winter and early Spring, the days start to get warmer. Every day the temperature is above approximately 50 degrees F, the flower bud grows and develops a bit more. Finally, when there have been enough hours warm enough for growth, development is complete and the blossom unfolds.

We know it's accumulated warming that makes the difference, because if it was just the increasing daylength, Spring flowers would bloom on the same date each year. They don't. They bloom earlier in a warm Spring and later in a cool one.

It turns out you can calculate the amount of heat a Spring flowering plant is receiving using a measure called degree days. You add up all the hours since January 1st that the air temperature has been above 50 degrees F and divide by 24 to get a measure called a growing degree day. But since we're interested in bumblebees, we'll call them bee degree days. You can read more about degree days and how to calculate them HERE and HERE.

So if we, or the bumblebee, can keep track of the number of bee degree days, we can predict when the flowers will appear. Each species of flowering plant seems to have its own, unique required number of degree days for blossoming.

Hibernating bumblebees, of course, do not use computers and trig functions to calculate bee degree days. In all likelihood, some aspect of their internal body chemistry changes slowly when the temperature is warm enough. After enough warm days, the chemistry has changed enough to wake up the slumbering queen.

Soon she's on her way, in search of that first, quick pick-me-up of fresh Spring nectar.

[Photo by Tony Wills, CC License]

Bumblebee Mating

Not exactly seasonal, but I wanted to show you this photo, sent to me by a friend, of Common Eastern Bumblebees (Bombus impatiens) mating last Fall.

The queen is the larger individual, clinging to the edge of a leaf, and the considerably smaller male is hanging below her.

By mid- to late summer, new virgin queen and male bumblebees are produced from successful colonies. These individuals leave the nest and seek each other out for purposes of reproduction.

Mate seeking in bumblebees was first recorded by Charles Darwin who set his children the task of following male bumblebees in his garden to record their behavior. The males of most species patrol a route which they mark with scent produced by their labial glands. The pheromone is deposited on "leaves, prominent stones, fence posts or tree trunks" according to Dave Goulson in his book, 'Bumblebees: Behaviour, Biology and Conservation'. It's not certain exactly how the newly emerged queen encounters the patrolling male. Presumably a combination of the species specific pheromone used for marking and the height above ground of the male's patrolling route provides the appropriate cue.

Observations are few, but presumably the male and female make contact in the air. Then, shortly after coupling, they alight until copulation is complete.

[Photo by Michelle Arsenault]

Queens Spring Into Action

Spring is the time for hope and for creating new life. But Spring can be the most dangerous period of the year for bumblebees.

We'll be seeing bumblebees on the wing soon (our colleagues in England are seeing them already), for Spring is when mated queens emerge from hibernation. Each has overwintered in a shallow burrow in the soil. Energized by the warming rays of the sun, each queen must crawl to the surface and fly off in search of a first meal of nectar to fuel the colony founding tasks that lie ahead.

But what if an unusually cold winter or Spring rains that flood the soil kill off most of the hibernators? What if there are no blossoms to forage after they emerge? What if too many queens have survived and there is not enough nectar to go around?

An uncertain environment and intense competition make each new Spring a challenge. This is why early bumblebee populations may be boom or bust - tens of thousands of queens in some years, few in others.

One strategy that bumblebees appear to have evolved in order to reduce competition for resources each Spring is staggering emergence times. North American bumblebees (like those in any temperate climate) can be characterized as either early-Spring, mid-Spring or late-Spring emergers.

Right: Emergence pattern for 3 common eastern North American bumblebee queens.

Because most wildflowers bloom at different times through the season, early emerging queens have access to a different initial food supply than those emerging later on. The result - more bumblebee species can co-exist in the same community than if they competed head on for every resource.