The relationship between plants and their pollinators is complex, not usually straight forward. Pollination Syndrome, the method by which plants have managed to attract some pollinators and discourage others is both fascinating and not fully understood.
Pollination is the mechanical transfer of pollen from the male parts of a flower to the female parts of a flower. Could be the same flower, could also be a flower of a completely unrelated species of plant. In other words, pollination is pollen moving around, not necessarily resulting in fertilization, even though we use it to mean that.
Why bees are great pollinators and why plants use Pollination Syndrome to encourage some pollinators over others is because bees don’t know how to pollinate. I know! Who’d have thunk it?
There is an incredible array of floral structures, colours, scents, pollen types, nectar and nectaries for bees to choose from and figure out. When a bee first visits a new flower type she has to figure out how to work it, where the pollen is, how to access the nectar, whether there is enough or the quality is right to make the effort; if it is and the bee succeeds in accessing the floral rewards it imprints upon the flower, it’s shape, colour, scent and so on. Then in a pattern of “flower constancy or faithfulness” the bee flies from that type to the next one like it, vastly increasing the likelihood of not just pollination but fertilization.
Many plants help their bee partners along by denying access to the average bee. The reward for figuring out the puzzle is a prize rich in pollen and nectar.
There are many examples of this. Digitalis or Foxglove nectaries are found at the end of long tubular floral structures that only long-tongued bee species like bumblebees can access. Also the interior of the blooms are filled with hair like growths that a large and strong bee like a bumble can push through to get to the nectaries which smaller bees can’t.
Plants also can create chemical boundaries as Pollination Syndromes. Asclepias tuberosa produces compounds poisonous to most organisms except the Monarch butterfly. Rhododendrons make a sugar that bumblebees can digest but other bees can’t. All in the name of rewarding their faithful pollinators.
Some plants take the opposite approach by being open to all comers. The rewards are few, little in the way of pollen or nectar, but access is uncomplicated. Examples are sunflowers. Watch a sunflower for only a few minutes and you’ll see many species of animals stop for a visit; beetles, birds, bees, flies and butterflies. The list is substantial.
Plant diversity is mirrored by pollinator diversity. Not all bees have the same set of skills and attributes. There are long, medium and short tongued bees. There are bees that are active mostly in the morning, during the day or the evening while others are active the whole day. Bees also gather pollen in differing ways. Honeybees and bumblebees tend to work flowers from the edge while mason bees when possible land right in the middle of the bloom.
It is interesting to note that flowers do not release their pollen and nectar at a constant rate. Plants have periods of the day when their pollen is available and other times of the day when they conserve their resources. For example Rosa multiflora releases the bulk of its pollen between 6:30 – 10:30 am while Verbena officinalis makes its pollen available between 7:00 am and 11:30 am.
The same with nectar. Buckwheat secretes nectar from 7:00 to noon daily. A friend of mine was scoffing at the notion that buckwheat is much of a honey plant here on the coast because he never saw bees on their flowers. In the morning he’d leave for work without checking what the bees were working and by the time he got home in the evening they’d long since moved onto to other blossoms.
Plants don’t get up and move around but the ecology of pollination and the relationship between plants and their pollinators is dynamic and in motion.
All this to say I am working on wildflower mixes to attract mason bees versus other bee species.
The challenge is there is an overlap between the characteristics of mason bees, what blooms they can access and are attracted to, and those of the honeybee. After careful study and observation I have come to the conclusion that if there are flowers in bloom within a three kilometer radius of a hive the honeybees will find it and exploit it. It’s what honeybees do. Given the distances honeybees can fly, how organized they are (a lot!) and how well they are able to manage in fractured and discontiguous ecologies they don’t need a huge amount of help in the foraging department.
Other bee species do need help. Some solitary native bee species are able to fly great distances, the Alkali bee for instance forages in a 9 mile radius from its nesting site, but that is more the exception than the rule. Most bee species, such as the mason bee, are not long distance foragers, they are doorstep foragers. Once they have established a nesting site they fly in about a 100 meter radius around that spot. This short-range gives them limited access to flowers, that and the fact there is a similarity between what they like and what honeybees like puts mason bees at nutritional risk from honeybee competition.
Both honeybees and mason bees are short tongued species. They are both generalist foragers.
Honeybees are much better at exploiting floral resources, able to communicate with each other to direct workers to meet colony needs, they require abundant amounts of nectar and pollen (60 lbs of pollen in a year and over 300 lbs of honey), when floral sources dry up or are inaccessible because of freezing weather, honeybees can regulate the energy needs of the colony to be temporarily independent of climatic conditions.
Mason bees have none of that going for them.
But they can fly at temperatures 2 – 3 º C lower than honeybees. Their pollen hairs are on the underside of their abdomens making them very fast at gathering pollen on the flowers that are a good fit for them. They have very low nectar needs, as a consequence are more attracted to flowers high in pollen but low in nectar.
It isn’t just food and access to it that are the issues between honeybees and mason bees. Increasingly honeybee diseases are jumping from honeybees to other bee species. I think the vector for this transmission are flowers. It’s just a guess on my part. When foraging pressure is high, not as many flowers for the number of bees in an area, there is a greater chance that a diseased honeybee will leave behind virus diseases in pollen or nectar on blooms. Unfortunately this is already the case with examples of bumblebees and mason bees catching honeybee diseases such as Acute Israeli Bee Paralysis Virus and Deformed Wing Virus. The ecological impact of these bee diseases has not yet been noticed but will surely come to our attention in a most disturbing way.
Historically there is some evidence that disease transmission between bee species is not a one way street. It is possible that Nosema cerana may have originated with an Asian bumblebee before jumping to Apis cerana and then to our honeybee, Apis mellifera. Chalkbrood disease in honeybees may have been originally a mason bee disease.
Before sharing my research, not yet concluded, I am posting this collection of flowers I think mason bees will benefit from gathered from the flower list at West Coast Seeds. I’m thinking of calling it “Spring Tonic for Mason Bees.” It does include some native wildflowers.
Fl2349 McKana Giant Mix Aquilegia spp.
FL2039 Coreopsis tinctoria
FL2597 Cynoglossum amabile
FL3291 Lunaria annua
FL2040 Blanketflower Gaillarida pulchella
FL3026 Violoa tricolor
FR830 Fragaria vesca