The study of phenology

I was walking along a country road this afternoon when I spotted a dandelion in full sun-drenched bloom. Right away I remembered it was time to plant potatoes. Although this may sound like an “old wives’ tale” these associations are based in fact.

Phenology is the study of periodic plant and animal life cycles in relation to seasonal changes in climate. It means that cyclic biological activity (things that happen every year) is often dependent on annual changes in temperature. Everyone has seen this. For example, cold weather until late in the spring means that flowers will bloom later.

Farmers have long known they could estimate planting times by looking at the wild plants. By continued observation of what happened and when, they compiled rules of thumb they could use for planting.

In my dandelion example, farmers learned that when the soil was warm enough to produce a dandelion bloom, it was warm enough to plant a potato “seed piece” in the ground.

A search through old almanacs and calendars will yield lots of these little gems, including associations that help predict flowering, ripening of fruits, unfolding of leaves, hatching of eggs, and bird migrations. More recently, phenology has been used to predict the effect of climate change on these and other annual biological events.

Who pollinates the daffodils?

This question has popped up several times recently, probably because daffodils are in bloom this time of year. Based on the fact that daffodils have large showy flowers, I assume that sometime in the distant past daffodils were pollinated by insects—probably bees.

But like most flowers that have been highly manipulated by plant breeders, daffodils are no longer particularly attractive to insects. The reason for this is simple. When it comes to ornamental flowers, plant breeders select for beauty. Daffodils, in particular, are selected for the color of the flower, the symmetry of the flower, the angle of the flower (does it face up or down), the size of the flower, and other arbitrary characteristics that daffodil judges look for.

Daffodils in vase. Photo by Rusty Burlew.

In selecting for these characteristics—and crossing them with individuals with other favorable characteristics—plant breeders have been able to produce an amazing variety of daffodils that run the gamut from white to yellow to orange to pink. Some of them are very beautiful and prized by collectors and flower aficionados alike.

Daffodil breeders hand-pollinate the flowers they want to cross and, if all works well, they will get a few seeds from each cross. These seeds are planted and tended for many years—I believe the average is about seven—before the bulb is large enough to produce a flower. Only then does the breeder get to see the results of his work. Once a flower is developed that the breeder wants to keep, it is reproduced by asexual reproduction—that is, the bulbs divide and produce new bulbs.

What you lose in this process are many of the characteristics that made the flower attractive to pollinators in the first place. By selecting only for beauty, for example, you may lose fragrance, sweet nectar, nutritious pollen—or any number of things that the pollinators liked.

Years ago, as a member of the Oregon Daffodil Society, I had the good fortune to meet one of the world’s foremost daffodil breeders. I asked her why she wasn’t worried about all her carefully recorded crosses becoming “contaminated” by pollen that might be carried by wind or animal pollinators. I was intrigued to learn that this wasn’t considered important because very rarely will these highly-bred flowers cross without human intervention.

This loss of pollinator-attracting features is not unique to daffodils but happens in all sorts of flowers from roses to pansies. It is the main reason why people interested in planting native bee habitat or wild pollinator habitat are encouraged to plant either native species or heirloom species that have not been highly manipulated. If you are unsure of a plant’s history, there are certain earmarks that point to intensive breeding. These include very large flowers, variegated flowers, flowers of unusual color, great size, long blooming period, or flowers known as “doubles” or “triples” with multiple sets of petals.

If you are trying to plant for pollinators, remember that many of the gardening catalogs mark the varieties that are attractive to pollinators. Also, stay alert when you see local plants that attract large numbers of pollinators—perhaps you can find the name of the variety from the owner or ask for a cutting or find out where the seed came from.

The important thing to remember is that the flowers most attractive to humans are often not those most attractive to pollinators.

Why bees pollinate plants that don’t need it

Cross pollination—the moving of pollen from the flowers of one plant to the flowers of another—is usually accomplished by wind or animals. There are a few other vectors, including water and gravity, but wind and animals are the main ones. Many animals move pollen—including bats, birds, and butterflies—but bees of one species or another do most of it.

Nevertheless, the bees don’t have any contracts or business deals with the plants. The foraging bees have a mission, and that mission is to go get something the colony needs and bring it back. The things the hive needs are pollen, nectar, water, and propolis, and there are feedback mechanisms and other communication systems that tell the foragers which of these they need to collect.

So given the mission to go forth and collect pollen, that’s what the forager does. She doesn’t give a rip about what the plant wants. Once she finds a satisfactory source of pollen, she collects it and brings it home. If the pollen comes from a wind-pollinated plant such as corn or alder, it makes no difference to the bee.

Plants that need cross pollination have evolved ways of attracting pollinators, including brightly colored petals, pleasing aromas, or plentiful nectar. (Technically speaking, the plants that had some of these characteristics were able to survive and reproduce more successfully than those which didn’t, so those genes increased in frequency in the gene pool.) In any case, the plants benefited from the insects and the insects benefited from the plants.

Plants that don’t need to attract pollinators usually don’t have showy flowers, nectar, or fragrance. They still need pollen in order to reproduce, but the wind takes care of moving it around. Some of these plants actually produce pollen that is toxic to bees, or that is not pleasing to them. Because producing pollen is energy-expensive for the plants, if they don’t need to share it with insects, it is best if it’s not attractive to them.

When you’re thinking about honey bees, the whole thing is made more complicated by the fact that honey bees are not native to North America, so the plants that are native here did not co-evolve with them. Honey bees are polylectic which just means they forage on many different species of plants. And for the most part, the wind-pollinated plants that produce “tasty” pollen just have to put up with them.

Wild pollinators cannot replace honey bees . . .

At least not in the way we’d like. In the past few years a flood of articles has heralded native pollinators as “saviors”—groups of selfless, tireless, seldom-seen gladiators that are going to step in and save our food supply once the honey bees die off.

This is a comforting thought, and perhaps one day native pollinators will shoulder the bulk of our pollination needs—but it won’t happen within our current system of agriculture. It can’t. Successful transition to native pollinators will require nothing short of a complete overall of our current farming system.

Bumble bee on ceoanthus. Photo by Rusty Burlew.

If you read about the biology and ecology of wild pollinators, you will see they can be very efficient in terms of the number of flowers pollinated per minute. So efficient, in fact, that you wonder why the heck we ever started using honey bees. But as you dig deeper, you will also see they have very different life cycles and habitat requirements.

Some native pollinators will forage only a few hundred yards from their homes while honey bees will easily cover a three-mile radius—even more if resources are scarce. Some native pollinators visit only one plant species, or several, while honey bees pollinate hundreds. Some native pollinators are active only a few weeks of the year while a honey bee colony will forage any time the weather permits. Most native pollinators live singly or in small groups while honey bees live in massive colonies. The list goes on.

In the “old days,” let’s say before the end of WWII, people who kept honey bees kept them for honey. And if you didn’t keep bees, you didn’t worry about pollination. In fact, no one paid any attention to pollinators because there was no shortage. A farmer planted a field, the pollinators did their thing, and a crop was harvested. Short-lived, picky pollinators weren’t a problem because there were hundreds of different kinds. There was always one or a dozen other species to pick up where the last one left off.

But the Green Revolution changed how we farm and, before long, there weren’t enough native pollinators to do the job. The fields were too big, the habitat was too scarce, and pesticides were everywhere. As farms got bigger and more mechanized, honey bees had to be trucked in along with other forms of migrant labor.

Even the people who are currently studying native pollinators concede that without significant changes, native bees might supplement—but not supplant—honey bees. Some experts estimate that up to 30% of the farmland would have to be converted to bee habitat. Hedgerows, borders, and habitat strips would have to be interspersed with crops. This reserved land would need to remain un-tilled and be planted with large numbers of flowering plants so that something was always in bloom.

Thing is, even with all those resources devoted to wild species, it might not be enough. We would have to change pesticide practices, stop poisoning roadside weeds, and eliminate larger-than-life fields. We would have to become stewards—rather than pillagers—of the land.

I wouldn’t want to discourage anyone from keeping a hive of honey bees or tacking a bee block to a fencepost. But even thousands of them won’t assure a future food supply. To do that we must change the way we farm—from endless rows of monoculture to GMOs to weed control—it all has to be fixed. Native pollinators can’t save us unless we save them first. Care of pollinators needs to be job one.

Buy seeds, not ‘cides

While you peruse the seed catalogs in the coming weeks, don’t forget to provide food and habitat for beneficial insects such as lacewings, lady bugs, stink bugs, hover flies, assassin bugs, and parasitic wasps. By attracting beneficials to our gardens, we can get away from using insecticide . . . and avoiding insecticide is the very best thing we can do for our bees.

Good Bug Blooms

Beneficial insects are the ones that eat critters we don’t want in our gardens—pests like aphids, beetles, mealybugs, mites, thrips, leafhoppers, and grubs. But to keep the beneficials around, we must provide good homes for them, as well as a plentiful supply of flowers. Flowers that produce pollen and nectar provide the nutrients adult beneficials need to produce large numbers of eggs—all of which turn into aphid-munching, grub-slurping larvae.

Even when the “meat” is in short supply—as when they’ve eaten all your aphids—many of the beneficial species consume nectar as a source of carbohydrates and pollen as a source of fats, proteins, vitamins, and minerals. To keep your beneficials happy throughout the growing season, you must provide a succession of flowers. Something must always be in bloom.

Conveniently for us, the Hudson Valley Seed Library has packaged a seed mix called “Good Bug Blooms.” Each packet contains cosmos, annual gaillardia, zinnias, blue cornflower, sweet alyssum, flax, chamomile, and several other varieties of beneficial bug food—500 seeds in all. Not only that, but the packets themselves are gorgeous works of art. As the seed library states it, “Heirloom Seeds and Contemporary Art, All in One Pack.”

By the way, it’s easy to get lost in the stacks at the Hudson Valley Seed Library. Have a look around their website—you’ll surely come away with more than one packet of seeds.

USDA updates hardiness zones

Last Wednesday the USDA released its newly redrawn Plant Hardiness Zone Map. The map is based on the average lowest winter temperature in a given area—not the lowest temperature ever—and is calculated from data collected over the last 30 years. The new map was compiled at Oregon State University using GIS software.

Plant Hardiness Zones are used by gardeners, nurseries, farmers, or just about anyone who wants to know if a particular plant will thrive in a particular area. They are also used by scientists studying changes in animal distribution or the spread of invasive species, insects, and plant pathogens. A variety of federal and state agencies also use the information for projects and predictions.

The USDA is careful to say that the new map is not useful for studying climate change, and it points out the many of the changes in the map are due to better technology and better data manipulation. However, it is interesting to note that many areas in the United States were bumped into a warmer zone, and two new zones were added at the high end of the scale. The new zone 12 has average low temperatures of 50-60°F, and the new zone 13 has average low temperatures of 60-70°F.

It seems to me that if the changes were due solely to better data collection, the changes would occur in both directions—some areas would drop into a colder zone, some would rise into a warmer zone, and some would remain the same. But according to the sources I’ve read, the changes were nearly all in the warmer direction. And if two warmer zones had to be added—not just one—it means that some areas have average low winter temperatures that are more than 10 degrees warmer than previously calculated. That’s hard to explain by bad data.

New USDA Hardiness Zones 2012

The warmer map has several implications for native bees. For one thing, flowers may bloom earlier than they used to, especially in northern areas, and the growing season may be slightly longer. The mix of available forage may change as plants, previously confined to the south, slowly expand their distribution.

The bad news is that warmer summer temperatures my desiccate some of the plants that previously provided forage, and warmer winter temperatures may allow the spread of competing insects into regions where freezing temperatures once prevented overwintering. Even the northern spread of Africanized honey bees can be accelerated by slightly warmer winter temperatures. All very interesting . . . and all very messy.

Follow this link to the interactive map where you can enter your zip code to find the details of your hardiness zone.

Legend for USDA hardiness zone map 2012.

Tiny bee builds flower-petal nests

Scientists in Turkey and Iran recently discovered a tiny bee that uses flower petals to build nest capsules. The bee, Osmia avoseta, uses only the petals of Onobrychis viciifolia for this important work.

I somehow missed this story, which was run by NPR on May 6, 2010. But it’s not too late to follow the link and see a fascinating series of photos by Jerome Rozen of the American Museum of Natural History. It is well worth a look.

The fertile female O. avoseta builds about ten of these petal nests in a cluster. The cluster itself is in the bottom of a thumb-size burrow in the ground. One by one she collects chunks of petals and laminates them together, cemented by thin layers of mud.

Once a capsule is complete, she provisions it with a mound of nectar and pollen and, like other Osmia females, lays a single egg on top of the provision. She then seals the open end of the capsule to protect it from environment dangers. Once the capsules are complete, the eggs transform into larvae and then pupae. The pupae spin a cocoon inside the capsule before eventually becoming adult bees.

The petal-donor, Onobrychis viciifolia (also known as sainfoin) is a perennial legume native to Eurasia. It has been cultivated widely for animal forage and is now found throughout the world. The flowers are pink, showy, and produce large amounts of both pollen and nectar, making it extremely attractive to many pollinators, including honey bees.

Tips for planting a pollinator garden

When planting a pollinator garden, keep in mind that pollinators need food during the entire growing season. Although some species live only a few weeks, different species become active at different times of the year. In other words, something must be in flower at all times throughout the spring, summer, and fall if you want to have a varied and continuous supply of visitors. Here are some tips for a successful pollinator garden.

  • The wider the variety of flowers you plant, the wider the variety of pollinators you will attract. Different pollinators are attracted to different plant features, so give them plenty of options.
  • Choose flowers of different colors. Bees are particularly fond of blue, purple, violet, white, and yellow. Hummingbirds, on the other hand, like the reds.
  • Flowers planted in clumps of like-kind tend to attract more pollinators than scattered mixtures.
  • Plant flowers of different shapes. Pollinators have an amazing variety of tongue lengths, mouths sizes, body sizes, and taste preferences. Flowers of various geometries attract a wider selection of pollinators.
  • Highly selected hybrids often have less nectar than heirloom varieties. Stick with heirlooms or native varieties, when possible.
  • Plants in the sun attract more pollinators than plants in the shade.
  • Sheltered plants are more favored than plants that thrash in the wind.
  • Have a source of mud readily available. Certain bees, such as mason bees, use it for sealing their nests.
  • Skip the pesticides—not good for them, not good for you.

Pollen can carry disease to native bees

While studying pesticides in pollen, I was always curious about the potential for pollen to carry disease organisms as well. Indeed, a study that appeared in the December 22, 2010 PLoS ONE confirmed my worst fears—that pollen may be a major route of viral infection from managed honey bees to wild native bees.

The authors of the study examined the four viruses that are most commonly found in North American honey bees—deformed-wing virus, sacbrood virus, black queen cell virus, and Kashmir bee virus—plus Israeli acute paralysis virus, which is often found in conjunction with colony collapse disorder. They asked a number of questions about bee-to-bee disease transmission and then set up a series of experiments to answer those questions.

They found eleven species of wild pollinators in Pennsylvania, New York, and Illinois that carried at least some of the viruses. These viruses were much more likely to show up in wild pollinators that lived near apiaries known to be infected with the various pathogens.

Tests on both the pollen and the bees themselves showed that in many cases disease-free foragers were carrying pollen loads that contained viral diseases—especially deformed-wing virus and sacbrood virus. This finding indicates that the pollen, itself, may be capable of transmitting the disease from one bee to another—it may not be necessary for an infected bee to pass the virus directly to another bee. Similar to human viruses that survive on door knobs, these bee viruses appear to survive on pollen grains.

In other experiments, honey bees and bumble bees kept in greenhouses were shown to transmit Israeli acute paralysis virus among themselves by simply foraging on the same flowers. The disease moved freely in both directions, from honey bees to bumble bees and from bumble bees to honey bees.

The authors point out that the exact mechanisms of disease transmission via flowers and pollen are not understood and more study is needed to see if host plants have a greater role in disease transmission than just as physical carriers. In the meantime, it is important for beekeepers to understand the impact diseased honey bees may have on wild pollinator populations. Honey bee health needs to be a priority of beekeepers if we are to maintain the health—or perhaps the very existence—of wild pollinator populations.

For more information, you can download the complete paper for free at

Cockerell’s bumble bee makes a comeback

In late August of 2011, along a weedy stretch of highway north of Cloudcroft, New Mexico, three bumble bees were plucked from the side of the road. The specimens, which were collected and identified by a team of entomologists from UC Riverside, turned out to be Cockerell’s bumble bees. “And what is so special about that?” you ask. Well, for starters, the last time these bees were seen was in 1956. That’s 55 years ago—a long time to do your own thing with nobody watching.

Cloudcroft is a town on the northern border of the Lincoln National Forest in south-central New Mexico. Cockerell’s bumble bee was originally discovered north of this area in 1913. Between 1913 and 1956 it was reported 16 more times in Cloudcroft as well as a few times in neighboring areas along the Rio Ruidoso and once in the town of Ruidoso. And then it disappeared.

Most of the bumble bee species in the United States are identified from hundreds, or even thousands, of specimens. But with so few specimens of the Cockerell’s bumble bee available for study, a number of entomologists dismissed it as merely a variant of a more common species, and so paid little attention over the years.

New genetic tools, however, have shown that the bee is a distinct species—one with an incredibly small range for a bumble bee. As far as the researchers can determine, the Cockerell’s bumble has been living in an area of less than 300 square miles—mostly in and around the Lincoln National Forest and nearby tribal lands. This protected and isolated habitat helped the bee survive down through the decades in spite of its extremely small natural range. Scientists say the bee is not endangered by habitat loss, at least not for now.

Cockerell's bumble bee. Photo by Greg Ballmer/UC Riverside.