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The strange sex lives of bees

By Isaac Weinberg

Most complex organisms, like humans, reproduce sexually. Sexual reproduction occurs when a sperm cell produced by a male fertilizes an egg cell produced by a female. Some organisms, like aphids, can reproduce asexually by undergoing a process known as parthenogenesis, where unfertilized eggs develop into fully functional organisms. Bees ants and wasps, however, reproduce using a combination of both strategies.

These closely related species, known as hymenopterans, must use both reproductive strategies because of their unique genetics. In most complex organisms, even those who reproduce using parthenogenesis, all individuals are diploid and have two sets of chromosomes. In hymenopterans, however, females are diploid and males are haploid, having only one set of chromosomes. Females arise from fertilized eggs, while males arise from unfertilized eggs. This unique sexual determination is called haplodiploidy. It is possible because the queen can selectively fertilize any egg she lays, and as such can determine whether each egg will develop into a male or a female.

Haplodiploidy is even weirder than it sounds because of the effects it has on each bee’s family tree. Every female bee develops following normal fertilization, and as such has a mother and a father. Male bees, known as drones, do not have a father, and receive 100% of their genetic code from their mothers. This in turn means that each female bee has two grandmothers, but only a single grandfather! Male bees not only have half the genetic material of their female counterparts, but are also less prevalent in the family tree!

This brings us to another quirk of haplodiploid reproduction. In sexually reproducing species, both sperm and egg cells are haploid. Both of these cell types are created through meiosis, a process by which diploid cells undergo a complex multistage reductional division. In hymenopterans, meiosis only occurs in female bees as the queen generates her eggs. Since drones are already haploid, their sperm cells do not need to undergo meiosis. Instead, each sperm cell contains an exact copy of the drone’s complete genome.

Where does the meiosis that generates those sperm cells occur? Within the queen as the egg that develops into a drone is produced! Putting all the pieces together, each drone is haploid, receives all its genetic material from a single parent, and is produced through meiosis. All features of a sperm cell in a species that reproduces using classical reproduction.

What is a sperm cell’s only purpose? Fertilization. Each drone leaves the nest in hope of finding a mate to pass his genes onto the next generation. If successful, each of his daughters will have inherited his complete genetic code – and will be equally related to his mother as to their own. His sons will inherit… nothing. Since each male is produced from an unfertilized egg, drones cannot have sons. The next time you see a drone sipping nectar from a flower, remember that his only purpose in life is to carry and pass on his mother’s genes to a new generation of daughters–some of whom will be future queens of their own colonies.

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Bee Mine: Pollinator Love Stories

The world of pollinators and flowers is full of love and heartbreak. For Valentine’s Day week, we’ve come up with some tales of romance to share: male honey bees that explode upon mating; hawkmoths that don’t pull their weight in the relationship; what happens when humans meddle with pollination; and more! Follow us on social media @PollinateTufts for daily updates ❤️

Bumble bees (*Bombus impatiens*) are in love with goldenrods.

Love is in the air …. and pollen – Jessie Thuma
On a crisp autumn morning, the bumble bee awakes at first light,
She suns herself at the entrance to her nest and prepares to take flight.

From her nest below the ground, she sets out through the meadow.
What flower will she choose first? Blue or purple or yellow?

She’s an early riser, and has her pick of flowers.
But she will wait for that special bouquet that holds her in its power.

As she flies between the trees,
She catches a sweet scent carried by the breeze.

A patch of goldenrod lit by the mid-morning sun,
Stalks of yellow flowers enticing bees with tasty pollen.

The worker slows to land, taking stock of her workplace,
The goldenrod welcomes her, flowers opening like a warm embrace.

As she moves from plant to plant her baskets fill with pollen,
But she leaves a little behind at each plant, setting seed for future blossom.

Flowers take the shape best suited to their companion bee,
And in return bees drop pollen between plants in a pollination jubilee.

Some flowers are so perfectly shaped that only a bumble bee can reach the pollen inside,
And for these plants the worker sings a sweet buzzing song coaxing the petals to open wide.

Bumble bees are loyal and will visit the same patch of flowers for weeks on end,
Once they are enticed to try the reward, that flower becomes a bee’s best friend.

The worker leaves when she can carry no more,
But she will be back tomorrow—that is for sure.

A honey bee drone. His huge eyes help him
find a queen to mate with, his only purpose in life! (PC: Karen Johns, Flickr)

The tragic love of a honey bee drone – Isaac Weinberg
Male honey bees–known as drones–have only one purpose: reproduction. They leave the nest in the spring and summer, using their massive eyes to tirelessly search for a queen to mate with. With each hive producing hundreds of drones, but only one or two queens, most drones fail to find a mate. Eventually, these unlucky males are barred from reentering the hive, and die within a few days, cold and alone. For the lucky few that find a mate, however, love is bittersweet. The male projects his love with such force that his reproductive organs explode with a loud audible “pop,” killing the lucky bee. Thus, for the drone, Lord Tennyson’s poem becomes the eternal question; Is it better to have loved and lost, than never to have loved at all?

Orchid bees come in combinations of brilliant and iridescent colors, including green, blue, purple, orange, and yellow! (PC: *Euglossa imperialis*; Flickr, USGS Bee Lab)

Orchid Bee Mine – Sylvie Finn
For many, Valentine’s Day is about indulgent gift giving. Maybe you’re thinking about getting your loved one an orchid, or perhaps a fancy perfume. Well, I hate to break it to you, but you’re a little late to the game on that idea. Orchid bees are the ultimate authority on Valentine’s Day gift giving. As their name suggests, male orchid bees have a special relationship with tropical orchids (Orchidaceae). Males are attracted to the sweet and specific volatiles of orchids and use special hairs on their front legs to collect the essential oils that produce the scents. The males then store these essential oils in large modified hind legs. Each species of orchid bee has its own “recipe” of scents to combine, creating the perfect perfume to woo a mate. Once the male bee has perfected his fragrance, he presents his perfume to females in the hopes of impressing her with his ultimate Valentine’s Day gift. If he’s lucky, his perfume will be so complex and impressive that the female orchid bee will choose him as her valentine.

Tobacco hornworm moths are nocturnal pollinators. (PC: Mike Lewinski, Flickr)

You take too much in this relationship – Adam Pepi
Hawkmoths are nocturnal pollinators of many plant species, including the fragrant night-opening flowers of wild tobacco. The pollination is beneficial for the tobacco plants, but sometimes the moths leave an unpleasant gift behind: their offspring. Hawkmoths deposit eggs on tobacco plants, which develop into giant caterpillars (also known as hornworms), devouring the leaves of the tobacco. This makes this a risky deal for the tobacco, but they have other options: tobacco plants that are attacked by caterpillars keep their flowers closed at night so that the hawkmoths aren’t attracted, and instead open their flowers during the day to attract hummingbirds. We can learn something from the tobacco plant this Valentine’s Day–don’t let the hawkmoth in your life hold you back.

Bicolored striped-sweat bees (*Agapostemon virescens*) are faithful partners of wild roses.

Roses and bees–a love story a million years in the making – Nick Dorian
It wouldn’t be Valentine’s day without roses. But the roses you pick up for your honey are a far cry from the roses a bee visits in a meadow. Wild roses are simple and straightforward: five white or light pink petals open to the sky, a delicate fragrance, with pollen-laden anthers and corollas full of nectar. These flowers look and smell this way as the result of a love story with bees millions of years in the making. In contrast, ornamental roses show what happens when humans meddle with this relationship. Through careful breeding over thousands of years, we’ve managed to accentuate all the flower traits that we deem desirable, and discarded those we deem undesirable. A swirl of lipstick red petals, a hyper-intense fragrance, and no messy pollen or sticky nectar to speak of–something a bee would never recognize as her faithful lover! As a result, ornamental roses are entirely dependent on humans for reproduction. Ornamental roses may win our hearts, but it’s safe to say their long-term relationship with bees is over for good.

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Where do wild bees go in winter?

In mid-October, gardens are abuzz with wild bees—eastern carpenter bees, bicolored striped-sweat bees, and common eastern bumble bee queens, to name a few. After mating, those bees have one goal: fatten up before winter. They are getting ready to hibernate for the next six months, and every flower counts.

fall bees fueling up on new england aster before winter — Fall active bees love fueling up on New England aster (*Symphyotrichum novae-angliae*) before winter. From left to right: *Agapostemon* sp., *Halictus ligatus*, *Bombus impatiens*.

Cueing into dropping temperatures and shorter days, the bees tuck away in quiet, secluded spots. Think: under leaves, rotting logs, long forgotten debris piles, or even back in their natal nests. Once in their resting place, they enter diapause—a state of lower metabolic activity—and cross their antennae. They will need enough energy to survive the next six months before spring.

Importantly, unlike honey bees, wild bees—of which there are more than 350 kinds in New England—are not active during winter. They cannot exit and re-enter diapause during a warm spell in February. Breaking hibernation before spring is a death sentence, and bees have many checks in place to ensure that this does not happen.

Although some species (like those mentioned above) actively fuel up before winter, most take a different strategy: they remain in their natal nest, surviving entirely on the nutrient-rich provisions left by mom. They have never seen the bright beautiful world. These bees will remain in the dark confines of their nest until emergence the following year.

Most wild bees overwinter in brood cells in their natal nest.

Bees that emerge in the spring overwinter as adults. In the fall, larvae metamorphose into adults before winter (yes, just like butterflies, bees undergo metamorphosis). They overwinter as adults in the nest, emerging when the temperatures rise in spring. For example, unequal cellophane bees Colletes inaequalis are harbingers of spring to eastern North America, emerging when there’s still snow on the ground because they overwintered as ready adults.

In contrast, bees that emerge in summer or fall hibernate as post-feeding larvae, also known as prepupae. Prepupae resume development after winter and pupating into adults sometime the following summer. Adults emerge when their favorite flowers are in bloom, but it is still a grand mystery how late-season solitary bees time their emergence so perfectly. Each year, when goldenrod blooms in our gardens in early August, hairy-banded mining bees Andrena hirticincta are there without fail.

Hairy-banded mining bees (*Andrena hirticincta*) female nectaring on goldenrod. This fall-active species overwinters as prepupae in the soil and develops into adults after winter.

Hibernating bees may be out of sight, but they can’t be out of mind. Think of the bee life cycle like a series circuit: if a single connection goes faulty, if a single life stage goes unsupported, all the little lights on our summer flowers go out. In this way, ensuring bees survive the winter is as important as ensuring adults find flowers in your garden in summer. Knowing how bees survive the winter, then taking intentional actions informed by this knowledge is the way forward:

Plant fall blooming native plants: Asters and goldenrods are fountains of energy-rich nectar. Bees that fuel up before winter require enough fall-blooming flowers to build sufficient fat reserves. The very best pollinator gardens bloom until frost.
#Leavetheleaves: Provide undisturbed nesting sites like patches of soil insulated with fallen leaves or intact hollow stems the right way. Resist the urge to neaten up your yard. Leave it messy until May and the bees will thank you. (Posting signage can help others know your good intentions!)
Pay attention: And last, take time to notice wild bees in your gardens in fall. Are females drinking nectar, or are they still collecting pollen and provisioning nests? What flowers do they like best? Or maybe you spotted bumble bee queens digging their winter hibernacula (if so, get in touch with Queen Quest)? Often the most important life stages are the ones hiding in plain sight.