Wild bee diversity and pollination services: Are cities a refuge?

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Bumblebee on Joe Pye Weed. Photo credit: flickr user mwms1916

Bee specialist Prof. Scott MacIvor’s presentation to the Hamilton Naturalists Club at the RBG on Monday April 9 was packed with useful information. This article attempts to distill most of his two-hour talk and provide links for the those wanting to learn more about the role of bees in the urban environment.

Common carpenter bee on New England Aster. Photos from http://www.toronto-wildlife.com/Insects/Bees_Wasps/Bees/bees.html

Prof. MacIvor’s overall message is, yes, our little city gardens and parkettes are important–not simply because cities provide a (relatively) pesticide-free environment but also because bees are actually adapting to urban materials and conditions. For example, bees have been observed using brake linings and window caulking for nest sites and material. This type of adaption is not surprising when we consider the bee’s evolutionary time-scale: 100 years = 100 generations. As well, because of the urban heat-island effect, our widely-planted native Redbud trees are now flowering weeks earlier and longer, providing more food for the early-emerging bees.
Prof. MacIvor wove several of these subtle lessons in evolutionary biology into his lecture. Before bees evolved to eat pollen and nectar,flowers relied on wind and rain to move pollen from anther to pistil. (http://biology4isc.weebly.com/uploads/9/0/8/0/9080078/5027982.jpg?839) Studies have shown that a plant’s fecundity improves not only with the number of visits from bees but also, surprisingly, the number of different species of bee that visit! It is not difficult to attract many bee species to our gardens–in southwestern Ontario we have 90% of the 360+ species of bees found in Canada, and six of the seven bee “families” are represented in southwestern Ontario.
As the climate crisis mounts, etymologists see increasing numbers of southern species moving north into Ontario. Two new species, in particular, are expected to show up in the GTHA in 2018.
Not only does bee-enhanced cross pollination improve the plants’ genetic vigor, bees help the self-fertile plants (such as peppers and tomatoes) as well. “Buzz pollination” happens when bees land on a flower, even a closed one, buzzing and vibrating at a frequency that shakes loose and distributes the pollen inside. Some it becomes available to the bee who may poke or cut her way in.
A little info tidbit: bees cannot “see” the colour red. So red plants such as Lobelia cardinalis are reserved for hummingbirds which enjoy the nectar with no bee competition.
Only female bees, across all species, are capable of stinging, which they do very reluctantly. Almost all bee stings are actually from wasps. Most bee species have barbed stingers which, when used, result in death to the bee–the stinger and part of the bee’s abdomen remain embedded in the skin. Some types, called “tickle bees” have stingers that are incapable of piercing human skin.
Almost all native bees (except for certain bumblebee species) are solitary, not social. There is no hive, no hierarchy, no queen. For solitary species, every female is a “queen” who does all the work: mating, feeding, nest-finding, and egg-laying. Solitary bees, which comprise the majority of our native species, do this all in the span of a single season.
If you have carpenter bees, do not worry that they’ll destroy your house. Like other solitary bees, they have a one-season lifespan so they don’t excavate more than a few inches and their holes will be re-used by a subsequent generation.
Carpenters and other above-ground dwelling bees will use holes in dead wood and tree trunks (sometimes created by beetles the previous year) as well as hollow plant stems. So it is important to leave your garden messy in the fall so the overwintering larvae don’t get discarded into the brown bag or compost bin. To tidy up the garden in the spring, cut the stalks close to the ground and lay them in bundles in a sunny spot. The bees will wake up in the appropriate environment.
If you want to provide a bee box or “hotel” be sure it is built with holes or hollow stems of the appropriate diameter and length. The length should be no more than 7 or 8”. Because the female larvae are deposited first (deepest in the hole) a too-short hole (less than 6”) will result in fewer females. Bees, depending on the species, will use holes between one millimeter and one centimeter in diameter. It is best to not use fresh wood from conifers, because flowing sap and rough edges can impede entry and exit. Anything that allows for a smooth inside wall and a deep hole closed at one end will work. There are resources and bee-box plans available online. Here are some reliable ones: http://www.xerces.org/wp-content/uploads/2008/11/nests_for_native_bees_fact_sheet_xerces_society.pdf
Ground dwelling bees are threatened by our love of mulch. Imagine waking up in the spring with 4” of impenetrable woodchips on top of your house! Leave portions of your garden with bare, uncompacted soil to provide safe nesting sites. Many species will use the same area.
The leafcutter group of bees needs leaves, of course, to make nesting material. So accept some leaf “damage” in your garden.
Honeybees are the domestic livestock of the bee world– and, unlike our native bees, they are not “in trouble”. Honeybees and our native species do not play nice. Bumble bees, our only native social (colony forming) species, live in groups of up to 200 individuals, easily out-competed by a typical honeybee nest of several thousand. As well, honeybees transfer diseases and mites to our native bee species.
What can we do to help our native bees? Prof. MacIvor gave a list of five things:

  1. plant flowers. Open, simple, non-complex with unobstructed “landing pads”.
  2. mow less. Leave open, bare ground for ground nesters. Make wood piles, not woodchips
  3. leave the mess for nesting places and nesting material. Cut plant residue late in spring, bundle and leave (entire) stems on site, in a sunny spot.
  4. provide a warm sunny place of rocks or logs. If you build a rock wall, site it facing south
  5. talk to your neighbours. A study of Montreal neighbourhoods showed that entire streets become heterogeneous– distinct from other nearby streets, and the presence of even a few nature-friendly gardens will inspire neighbours to do the same.

The Xerces society is a reliable online source for information on bees. “Managing Alternative Pollinators” is available here: https://xerces.org/books-managing-alternative-pollinators/ If you’re interested in bee identification, check out: “Bees of Toronto” https://www.toronto.ca/wp-content/uploads/2017/08/8eb7-Biodiversity-BeesBook-Division-Planning-And-Development.pdf