Long-time readers of my blog know that I think natural history notes are one of the most important parts of the scientific literature! Sadly, very few journals will publish them.
Luckily the Ecological Society of America does appreciate the value of natural history observations. I first submitted this note to Frontiers in Ecology and Environment for their Natural History Notes series. Unfortunately, the Frontiers series was about to close and they weren’t taking any submissions. But the editor suggested I submit my note to Ecology, where they were just about to start a new series called The Scientific Naturalist. So here it is.
Unfortunately it’s not open access and doesn’t have an abstract. So I’ve written a shorter note about my short note below; please email me if you’d like a copy of the original.
I love scientific serendipity. In the summer of 2015, we were living in Albury in southern New South Wales. Our street was lined with Corymbia trees, the iconic pink- and red-flowering gums.
The blossoms are attractive to all sorts of birds and insects and I spent a fair bit of time loitering on the street to get some good bee photos. I saw native bee species I’d never seen in my neighbourhood before, and never saw again after the Corymbia bloom finished. (How do they know the flowers are out? And where do they come from?!)
When fully open, Corymbia blossoms are huge and dish shaped with the male and female parts set apart from each other. It’s pretty clear that something large and hairy would be needed to pollinate them.
I watched smaller native bees deftly manoeuvre themselves into the flower dish to sup on nectar, often without touching any of the anthers, or the sticky stigma waiting for some pollen.
One day I noticed an opening blossom that was covered in a frenzy of tiny Hylaeine bees. Then I saw another one, and another. These blossoms hadn’t popped open yet, and all the pollen-covered anthers were still hidden inside the opening flower. The bees were having a great time, crawling in and out of the flower and over the top of each other to get the pollen.
It’s unlikely that the bees were pollinating the blossoms, as the stigma on most eucalypt blossoms doesn’t become receptive until after the flower opens. The most likely explanation is that I had caught some little pollen thieves in the act. And, judging by the frequency of the activity, and the fact that I saw the same thing happen again the following year, this probably happens a lot.
Because most pollination studies have been conducted on open flowers, there isn’t a lot of information about how pollinators interact with unopened or opening flowers. However, there are a handful of interesting examples in the literature of small bees visiting unopened flowers, sometimes even pollinating them in the process.
Yamaji & Ohsawa (2015) published the first report of pollination by sneaky bees, which they call ‘breaking bud pollination’, in an Asian lily species. The bees (Lasioglossum japonicum) enter the unopened flower through tiny gaps in the top of the bud, just as it breaks open, and slip inside to collect pollen.
A few other reports of impatient bees are published in the literature, but none of these show evidence of pollination:
Wall et al. (2002) document another Lasioglossum species prising open flowers of Xyris tenneseensis in Alabama, to get first access to the floral rewards.
Hurd & Linsley (1963) observed small solitary bees (Perdita hurdi) repeatedly piercing flowers of the unicorn plant (Proboscidea arenaria) in Arizona to rob pollen. The authors don’t document pollination success, but do speculate that pollination might be possible if the pollen-covered bees then move to another open flower to drink nectar.
Newman & Jacobi (2011) and Jacobi & Newman (2012) are the only records I know from Australia (thanks to Bernhard Jacobi for pointing me to these records, and for identifying my own sneaky bees!). These records document the same group of bees I observed (Hylaeine or masked bees) cutting open unopened flowers of Eucalyptus infera and two Grevillea species, respectively. In these cases, it’s more likely the bees were jumping the queue, not pollinating.
So tiny bees are more adept at getting access to unopened flowers. How often does this occur? Is this an adaptation or opportunistic behaviour? Is it a response to local availability of floral resources? What are the evolutionary advantages for bees and flowers? Is it more common in species with certain functional traits?
So many questions!
© Manu Saunders 2017
Do your Hylaeine bees carry their pollen internally too? I’ve never understood how they can be effective pollinators when they carry their pollen internally and are relatively hairless, but apparently they are very important for some Hawaiian species.
Yes they do. Most species have some hairs on the body and would carry a small amount of pollen between flowers. I’ve read that when hylaeine bees mostly clean the pollen off their head and forelegs to eat and leave anything on the rest of the body…not sure if that’s accurate. I expect most species make a very small contribution to pollination, if any, but I guess in the case of the Hawaiian hylaeus, they are mostly endemic and have evolved with the plants there, so there might be stronger relationships. I think there are plenty of research questions to answer about hylaeine bees! 🙂
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