If you have been following our ongoing Blossom Watch project (and if not, you should be!) or have spent any time outside in the last few weeks, you’ll know that many of our city’s magnificent fruit trees are in full bloom.
Though blossoms may play second fiddle to a hot slice of apple pie in autumn, it’s hard to deny the visual pleasure they add to a springtime Sunday stroll. Blossom-gazing may inspire the budding philosophers among us to muse on beauty or the ephemerality of existence, but rarely do we dwell too deeply on the alchemy that transforms flowers to fruit, and it is all too easy to ignore the labour of those hard-working pollinators that help the process along. At Not Far From The Tree, we believe in giving credit where credit is due, and so we are dedicating a three-part series of blog posts to celebrate the tiny little unsung heroes of fruit production: bees.
Earlier this week, we posted some information about the roles of bees as pollinators. Today we will continue that discussion by adding the input from two Toronto-based melittologists (wild bee biologists) who we’ve recently spoken with. Laurence Packer runs a large bee research lab at York University, and his collection represents 85% of the known genera of bees (Laurence estimates that there may be as many as almost 30,000 of species of bees worldwide, and around 400 within Toronto alone). Scott MacIvor is a PHD student who studies ecological networks of bees and wasps in urban and disturbed areas, and manages over 200 wild bee nestboxes around the GTA. In subsequent posts we will publish some of their conversations about wild bee habitats, the threats facing urban bees, and why (against all intuition and logic), it might be a good idea to attract wasps into your backyard. Today, we’ll draw some basic connections between wild bees, honey bees, and fruit.
SCOTT: Fruit trees are essential pollen and nectar resources for early season bees. Apples, for instance, have very non-complex flowers that make pollen and nectar really easy to access for bees. Fruit trees have a much larger number of flowers than shrubs or little garden patches do. So the sheer bulk of pollen and nectar that fruit trees provide is very helpful in terms of maintaining lots of resources in city landscapes. A lot of the initiatives to promote pollinators in cities, like pollinator gardens, tend to focus more on flowering plants that flower in summer, and not in spring. That is where fruit trees come in, as an opportunity to really boost up our pollen and nectar resources in spring.
LAURENCE: There was a recent survey of which crops are dependent upon which pollinators (Garibaldi et al, 2013). Most berries, and most tree fruits are dependent to some extent on pollination. Some of them are over 95%, some of them less than that. Grapes are brought to us by wind pollination, and so they don’t need pollinators, but most of the other common fruits are.
SCOTT: Fruit trees are essential to bees, but bees are also essential for fruit trees. There is a lot of data to show that fruit yield, the size, the quality, and the number of fruits for most fruiting species is entirely dependent on the effectiveness and the amount of pollination that occurs on any one flower in the tree. A lot of fruit trees can’t self-start, they require pollination from tree to tree. Lots of animals (flies, beetles, and birds) will also be pollinating fruit trees, but bees are the essential pollinators. There is lots of published material on apple pollination and cherry pollination, all supporting the fact that the diversity of bees in the landscape and the frequency of visits to each flower, can improve the yield of fruit trees, even wind-pollinated ones. You can envision a grape cluster, they are selfing all over the place, they are just depositing pollen on one another’s flowers, same with strawberries, but their yield is still improved by the presence of bees as pollinators who increase the effectiveness of that pollination.
LAURENCE: Most of the commercial berries and fruit trees produced through agriculture require pollination by an insect. Depending upon what the crop is, different insects are more effective at different plants. In many cases of commercial agriculture, honey bees are the insects used. There are plenty of crops where honey bees are not as effective as wild bees, but an advantage they have is that you can easily transport them around in hives of tens of thousands. Even if each honey bee’s visit to a single flower does not result in much pollination, you have a weight in numbers, there are so many of them that the total effect is usually good. If you have a handful of solitary wild bees nesting in the ground, each of which does a really great job at pollinating, they’ll still be swamped in their effectiveness by ten thousand honey bees, each of which is doing a bad job. Wild bees are often more effective per visit, but they are often more difficult to manage and so you don’t get them being used in agricultural settings so often.
Maybe 80% of the domesticated honey bee hives in the United States were moved to California to pollinate the almonds in March. They will then get taken to highbush blueberry in the Southeast for April and then maybe to Apple crops further north in May. Vast numbers of colonies are travelling vast distances, and imagine a situation where you are feeding your kids nothing but almonds one month, nothing but blueberries the next month, and nothing but apples the next month, and between one crop and the next we’ve got 10,000 kids saying are we there yet? So I think the way they look after them in the U.S. stresses the bees out a fair bit also. It is an all eggs in one basket approach. There is much less of that kind of transportation here in Canada and so that is one of the reasons why Canadian beekeepers have been suffering a bit less than the beekeepers. In Canada, people in generally are much better to their bees than they are in the U.S. Part of the reason for that is that you have to be because the climate here is so awful (that they have to pay more attention).
One of the smoking guns with colony collapse disorder was the new pesticides that started being used. It is my impression that the evidence that these new pesticides are at least partly responsible for the colony collapse disorder is now strong, but it is unlikely that pesticides are the only cause for the colony loss that we are seeing. There have been new diseases that have been brought into North America and other parts of the world as a result of people transporting honey bees in vast numbers. That causes a bit of a double whammy effect, because it seems likely that with these new pesticides one of their effects is to reduce the bees’ immune system efficiency. When you have got new diseases and your immune system is compromised, that means you are in worse shape.
SCOTT: The ecology of urban wild bees is super new, but essential to people like [those involved with] Not Far From The Tree and people who are doing food production, urban agriculture, and food security. If you have got 150 species of bee that all pollinate, and then a whole bunch of Walmarts go up or climate change kills off a quarter of them, we still have three quarters left. If we put all our eggs in one basket and focus on honey bees, and ramp up the number of colonies because honey prices are so high right now, we may be shooting ourselves in the foot, if some crazy honey bee genetic disease comes around and wipes out the honeybees then we will have not paid enough attention to maintaining the health of the wild bees.
People are getting a lot more interested in wild bees, but we still paint them with a very broad stroke. Someone may say that bees are declining in urban landscapes and do badly, but you have to look at the whole assemblage. There may be 75% of the bees that are declining, but then there is 25% that are just burning it, and doing amazing in cities. There are some species that may have traits that allow them to be plastic and live among us, collecting window caulking or living inside of brick walls. I should also mention that urban fruit trees, because we prune them, and maintain them, can actually be habitat for bees. Some species will actually nest in the old trunks of older trees or in dead sticks in canopies of newer trees. We have about 12-14 species of leaf-cutter bees in the city of Toronto, and a few of those will actually collect apple and cherry leaves to make their nests.
Laurence Packer is also the author of Keeping the Bees (2011), an excellent book that addresses some of the threats posed to bees around the world and seeks to dispel some common myths about these buzzing bugs (for instance: most bees are solitary, not social; only a small amount of species produce honey; many bees are stingless). Scott McIvor is a biology research coordinator with the school of Architecture, Landscape, & Design at University of Toronto. We’ll be hearing more from them in the next few weeks.