MAD BEE SKILLS: Built to Carry Pollen

IMG_9672Bees are the super pollinators, as they have a vested interest in pollen.

Interactions of co-dependence exist everywhere in the natural world, demonstrating that we are all a significant part of the overall life-giving function of Earth.  This year I will take you on a journey through the striking ways that bees are built to perceive and interact with their surroundings, making them essential to plant life, as well as animal life .  From lessons on carrying pollen, to smelling molecules, we will approach 2020 with a new appreciation for these tiny buzzing creatures.  Our first lesson begins with the story of pollen.

img_2688Powder containing hope of a future generation sits waiting for a taxi ride to its desired destination.

Pollen is half of the equation in plant reproduction, and must be transported to its destination by wind, water ,or pollinators. It is the male offerings in plant reproduction, while eggs are the female offerings. Pollen is composed of a hard shell (a wall consisting of an inner and outer shell) that protects its contents from destruction. It consists of proteins and fats. The challenge all pollen is faced with is transport to the eggs of corresponding flowers.

conifer pollen release

Image borrowed from: pollinator.ca

Wind has been used by plants since the dawn of botanical life on Earth. Wind transport is very inefficient, as most pollen is blown everywhere but its desired destination.  This form of pollen transportation is very expensive to the plants using it, as these plants must manufacture a lot of pollen to get the job done.

Interestingly, wind transported pollen is smooth and aerodynamic, sometimes even sporting air sacks, designed to catch the wind like a sail. Another well designed partnership in achieving pollen flight! Look at the electron micrographs of wind carried pollen grains in the images below.

Scanning electron micrographs of pollen grains from seven wind-pollinated gymnosperm species. (a) Á (c) Cunninghamia lanceolata , (a) equatorial view exhibiting oblate spheroidal shape due to natural dehydration after pollen dispersal in the air, (b) polar view with a sunken papilla-like protuberance in the middle, (c) exine with orbicules on the sculptured surface; (d) Á (f) Cryptomeria japonica . (d) equatorial view exhibiting ellipsoid shape, (e) polar view with a slightly sunken papilla-like protuberance in the middle, (f) many orbicules on the sculptured surface; (g) Á (i) Metasequoia glyptostroboides , (g) equatorial view exhibiting oblate spheroidal shape, (h) polar view with a slightly sunken papilla-like protuberance in the middle, (i) many orbicules on the sculptured surface; (j) Á (l) Chamaecyparis obtusa , (j) pollen grains with indentation due to natural drying after pollen release in the air, (k) single pollen grain showing oblate spheroidal shape with indentation, (l) many orbicules on the sculptured surface; (m) Á (o) Sabina chinensis , (m) many pollen grains with indentation due to natural drying after dispersal in the air, (n) single pollen grain showing oblate spheroidal shape with indentation, (o) many orbicules on the sculptured surface; (p) Á (r) Podocarpus macrophyllus , (p) equatorial view showing body and two sacci, (q) polar view with two sacci, (r) many small apertures on the surface; (s) Á (u) Cephalotaxus sinensis , (s) many pollen grains with indentation due to natural drying after release in the air, (t) single pollen grain showing oblate spheroidal shape with indentation, (u) many orbicules on the sculptured surface. Scale bars 0 50 m m (j, m, s), 10 m m (a, b, d, e, g, h, k, n, p, q, t), 5 m m (c, f, i, l, o, r, u). 

Image of wind carried pollen grains was borrowed from: “Adaptation of male reproductive structures to wind pollination in gymnosperms: Cones and pollen grains.
Canadian Journal of Plant Science 91(5):897-906 · September 2011 with 1,451 Reads

Pollinator assisted pollination is much more efficient, as the pollen is carried from its origin to its desired destination much more readily, at a higher success rate than wind transport.  Millions of years ago flowers developed, and became advertisements containing a sweet bait, nectar, consisting of sugar-water with vitamins, minerals and amino acids.

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Word about this sweet, energy packed food source spread, and a large group of interested seekers developed-pollinators. The number of pollinating species grew to 180,000, 20,000 of which are bees. All pollinators know about and seek nectar, but most know nothing of what they are doing to help plants reproduce, and have special characteristics that make them better helpers in this way.

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Many pollinators are hairy, feathery, or have some way of attracting and gripping pollen to their bodies, faces, or legs. Interestingly, pollen carried by pollinators has a Velcro-like surface, or the surface has deep grooves. These physical characteristics of pollen help pollen to get wedged in the hairs or feathers of pollinators. Bees are the focus of this article, and are super pollinators. Look at all that hair!

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Why is a bee a super pollinator? What do I mean by super pollinator? Bees are interested in collecting and carrying pollen, because they feed pollen and nectar to their young. They are built to carry their needs. I will get to how they transport nectar in the next article, but let’s get to how they are built and motivated to carry pollen.

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Most bees have hairs on their heads, thorax, abdomen, and sometimes legs. This isn’t just for show, the hairs serve two purposes.

The first function is to attract the pollen to the body of the bee.  This is achieved through electrostatic charge; the same trick you used to enjoy with a balloon and your hair. When the bee is in flight, the hairs generate positive charge all over the hairy parts of the bee. Flowers carry an electric field across the surface of the bloom, making pollen negatively charged. Opposites attract, and pollen will leap from the flower to the body of the bee, due to a large difference in charge between the two. An interesting fact here is some hairs on the bee have mechanoreceptors at the base of the shaft. Mechanoreceptors send signals to the brain in response to physical movement.  Mechanoreceptors on a bee are affected by the pull of very negatively charged pollen tugging on the positively charged hairs! Isn’t it cool enough that the hair and pollen carry opposite charges?!

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The second function of bee hair is to grip the attracted pollen. It isn’t enough that the pollen and hair are opposite in charge, because the charge on pollen will wear off, so physical characteristics step in to ensure effective transport.  Bee hairs are split and frayed along the shaft.  This characteristic makes it more likely the Velcro-like, or deeply grooved, surface of pollen will get wedged and stuck inside the forest of bee hair. The ways bee secure pollen for the long ride home varies.

pollen grains photo

A scanning electron microscope image of pollen grains from a variety of common plants, both wind and pollinator carried. William Crochot – Source and public domain notice at Dartmouth Electron Microscope Facility

Some bees such as honey bees and bumblebees have Corbicula (pollen baskets) on their hind legs. These structures consist of a solid smooth back with stiff rounded hairs the reach out and across the front of the smooth back. The pollen carried in this way is mixed with nectar to a Play Dough like consistency and stuffed into the Corbicula for transport. Not much pollen falls out of these pollen patties.

img_6246Look closely at lady honeybee’s hind leg, and you’ll see the Corbicula packed with a moist  pollen and nectar paste.

IMG_0023That orange ball the lady bumblebee’s hind leg is a mixture of pollen and nectar stuffed into her Corbicula.

Another way bees transport pollen is in thick hairs called Scopa. These hairs could be on the abdomen of bees or on the hind legs. In this mode of transport, pollen is loosely stuffed into the hairs, and readily pass off onto flowers visited by these bees.

IMG_7023This squash bee (Peponapis sp.) has Scopa on her hind legs, and you can see some pollen granules stuck to the hairs here.

img_4447This leaf cutter bee (Megachile sp.) has yellow pollen all over her abdominal Scopa.

The final way some, and very few, bees carry pollen is inside a transport tummy, which we will not go into any depth, as this will be next month’s topic.

IMG_7285This masked bee (Hylaeus sp.) carries pollen in her transport tummy, as she was born practically hairless.

I hope your mind was blown at least once in reading this post, and if so, share your knowledge with friends, family, strangers. Let’s get this movement buzzing louder than ever! Thank you for your continued support, following, and for joining the movement to advocate for native bees, and really all bees!

All photos, unless otherwise noted, belong to Jessica M Goldstrohm, owner of The Bees Waggle.