Protecting Pollinators

How to Save the Creatures that Feed Our World

Jodi Helmer

• Verlag: Island Press
• Jahr: 2019
• ISBN:
  9781610919371
• Thema: Biological Sciences
• Thema: Environmental Conservation & Protection

We should thank a pollinator at every meal. These diminutive creatures fertilize a third of the crops we eat. Yet half of the 200, 000 species of pollinators are threatened. Birds, bats, insects, and many other pollinators are disappearing, putting our entire food supply in jeopardy. In North America and Europe, bee populations have already plummeted by more than a third and the population of butterflies has declined 31 percent. Protecting Pollinators explores why the statistics have become so dire and how they can be reversed. Jodi Helmer breaks down the latest science on environmental threats and takes readers inside the most promising conservation initiatives. Efforts include famers reducing pesticides, cities creating butterfly highways, volunteers ripping up invasive plants, gardeners planting native flowers, and citizen scientists monitoring migration.Along with inspiring stories of revival and lessons from failed projects, readers will find practical tips to get involved. They will also be reminded of the magic of pollinators—not only the iconic monarch and dainty hummingbird, but the drab hawk moth and homely bats that are just as essential. Without pollinators, the world would be a duller, blander place. Helmer shows how we can make sure they are always fluttering, soaring, and buzzing around us.

CHAPTER 1

Bees and Beyond

WHEN BEES ALIGHT ON FLOWERS, something magical happens. Minute grains of pollen stick to their bodies while they gather nectar and, as the bees buzz about, moving from flower to flower, pollen grains are deposited on new flowers, triggering pollination. Though the entire process lasts mere seconds, our ecosystem depends on it.

Honeybees are credited with much of the work. Headlines like “Honey Bee Extinction Will Change Life as We Know It,” “The Plight of the Honeybee,” and “The World’s Food Supply Could Feel the Sting of Declining Bee Populations” perpetuate the idea that bees—and honeybees in particular—are the primary pollinators of global food crops. Honeybees are important pollinators; American beekeepers crisscross the nation every year, transporting billions of honeybees to pollinate crops ranging from apples and cucumbers to pumpkins and sunflowers. Upwards of 60 percent of commercial beekeepers in the United States travel to California between February and March to place hives among the trees in 1.3 million acres of almond orchards; apiarists bring hives from as far afield as Texas and Florida. But honeybees don’t deserve all of the credit for pollinating our favorite flora.

Worldwide, 200,000 different species tackle the task of pollination: vertebrates such as birds, bats, and small mammals make up a small percentage of the global pollinator population, while invertebrates such as flies, butterflies, beetles, moths, and, of course, bees make up the rest. The more widely recognized pollinators like monarch butterflies and honeybees tend to get the most attention. To wit, the honeybee is the face of the Cheerios brand and the star of the blockbuster animated film Bee Movie; monarch butterflies, with their striking orange, black, and white markings and their courageous migrations to reach overwintering grounds in milder climates, are emblazoned on the Non-GMO Project label and immortalized in coloring books and even tattoos.

While certain pollinators have been thrust into the spotlight, most of the 11,000 species of moths native to the United States fly under the radar, unrecognized despite being important pollinators. Consider the hawk moth (Sphingidae spp.). Thanks to their drab brown coloring, hawk moths are unimpressive at first glance, but looks can be deceiving. Their long, narrow wings make them fast and nimble in flight, and their tongues, which can measure up to fourteen inches long (the longest of all moth or butterfly species), make hawk moths adept at gathering nectar from flowers that would be off limits to other, less well-endowed pollinators. Because their larvae are green hornworms or tobacco worms, hawk moths are considered crop pests and often blasted with pesticides. The practice has devastated their populations, much to the relief of farmers and gardeners, but also to the detriment of rare plants like queen of the night cactus (Epiphyllum oxypetalum) and trumpet flower (Datura spp.) that depend on the long-tongued pollinator for reproduction. So, even as the unfortunate-looking hawk moth faces chemical attacks that threaten its survival, the race is on to protect prettier species like monarch butterflies and honeybees.

Box 1-1

Plant Sex

Pollination is simply the name for plant sex: plants need pollen to produce fruit, seeds, and new plants. For that to happen, pollen from the stamen, the male part of the flower, must be transferred to the pistil, the female part of the plant. The pistil is made up of the style, stigma, ovary, and ovules: the stigma receives the pollen, which travels down the style and into the ovary. After a flower is pollinated, the petals fall off; the ovaries become fruit and the ovules become seeds.

Self-pollination: Plants like orchids, peas, sunflowers, beans, and eggplants self-pollinate. Their male and female parts are located close together, making it easier for the flowers to move pollen from the stamen to the pistil. These plants can self-pollinate or be cross-pollinated (see below).

Thanks to “selfing,” rare plant species can still reproduce well even when there are few individual plants. This reproductive assurance benefits rare species and ensures their survival even if pollinators disappear from the landscape. Self-pollination also makes it possible for introduced species to invade new landscapes. In at least one study, invasive species of thistles were more likely to self-pollinate than the rarer native species of the same genus.

Wind pollination: Most agricultural crops, including grains like wheat, rice, corn, rye, barley, and oats, are wind pollinated; the breeze picks up nearly weightless grains of pollen and carries them from one flower to another. Plants that are pollinated in this way have lots of miniscule pollen grains but seldom have nectar.

Wind-pollinated plants seem to chase away animal pollinators; when these plants are growing in a landscape, pollinators are less attracted to those that depend on insects to reproduce. For one insect-pollinated plant species, red dead-nettle (Lamium purpureum), a study found that nearby wind-pollinated species reduced the amount of its nectar. The results led researchers to argue that future studies of plant–pollinator interactions should take all plant communities into consideration, not just species that rely on animal pollinators.

Cross-pollination: For pollination to occur in plants like cucumbers, carrots, melons, onions, squash, and cauliflower, pollinators must move pollen from one flower to another. Cross-pollination only occurs between two plants of the same species; pollen from a rosebush cannot pollinate a peony.

Buzz pollination: When bees grab onto a flower and flex their flight muscles, the flower vibrates, releasing pollen in a process called buzz pollination or sonication. Plants that are buzz pollinated, like tomatoes, eggplants, and potatoes, often have tubular anthers with narrow openings at one end; the pollen is small and too tightly packed to be accessible to all pollinators.

Issues with honeybees first came to light in 2006 when beekeepers started recording greater than normal colony losses with no apparent cause. These widespread hive abandonments were later attributed to Colony Collapse Disorder, or CCD. The colonies that succumbed to CCD, called “spring swindle disease” in historic literature, appeared healthy in the weeks leading up to the collapse. Without warning, the bees disappeared, leaving behind hives full of honey, pollen, bee bread, and capped brood. There was no evidence of dead adult bees—they simply abandoned the hive. Despite being responsible for 30-plus percent of colony losses—with beekeepers in some states attributing 90 percent of their losses to CCD—no specific causes have been identified, but several have been investigated. The first comprehensive survey of CCD losses evaluated sixty-one potential factors, from pesticides to pathogens like European foulbrood, varroa mites, and Nosema fungus, and found that no single stressor stood out as the sole cause of hive abandonment. (The study did show that CCD-affected colonies did have more pathogens and more types of pathogens than unaffected colonies.) Several other studies have since reached the same conclusions, attributing CCD to multiple stressors rather than a single cause.

Around the same time CCD was first identified, farmers began importing honeybees for the first time since 1922. Congress had passed the Honey Bee Act of 1922 in the hopes of preventing the import of hives with tracheal mites (Acarapis woodi). The mites, first reported in the United Kingdom in 1921, live in the tracheal tubes of honeybees and feed on their blood before burrowing through the tracheal tube walls and creating crusty lesions on the breathing tubes. In the earliest stages of infestation, colonies are largely unaffected. Bees traveling between hives (or between apiaries) can transfer the parasite. Tracheal mites affect flight efficiency, cause wing and abdominal deformities, and shorten lifespan. If more than 30 percent of the honeybees in a colony are infected, tracheal mites can be fatal to the entire colony. Fumigating the hive with menthol crystals, a crystalline alcohol extracted from peppermint oil, is the accepted method for controlling tracheal mites. Despite the congressional action, tracheal mites eventually did make their way to the United States. A commercial beekeeper in Texas reported the first infestation in 1984; the mites spread to seventeen states within a year.

News of CCD led Congress to change the terms of the Honey Bee Act of 1922, allowing the import of honeybees for the first time in a generation. Honeybees are native to Europe, not North America, so importing the species used to be commonplace. Farmers imported the iconic pollinators from Australia and New Zealand to help bridge the gap between winter losses and the early pollination season, particularly for the pollination of almond orchards in California.

The combined news of CCD and the appearance of tracheal mites led to some Armageddon-like predictions. With the number of US-managed honeybee colonies hovering around 2.5 million—down from 6 million in 1947—a 2012 report from the United States Department of Agriculture (USDA) warned that “the survivorship of honeybee colonies is too low for us to be confident in our ability to meet the pollination demands of U.S. agricultural crops…. We are one poor weather event or high winter bee loss away from a pollination disaster.” Predictions were made that a honeybee crisis could lead to a tenfold increase in food prices.

Though the number of honeybee colonies has dropped by more than half over the last 70 years—declines have been blamed on a host of factors, including habitat loss, pesticide use, and climate change—nevertheless the bees have started to bounce back from CCD. During the 2017–2018 winter season, commercial beekeepers lost 26.4 percent of their hives (acceptable winter losses were 20.6 percent for the same time period), but it’s not all good news for the little buzzers. These fragile creatures face serious risks to their survival. In addition to the essential role that honeybees play in agricultural production and maintaining biodiversity, scientists depend on honeybees to better understand changes in the ecosystem, including threats to general pollinator populations. In fact, most American scientific work on pollinators has focused on honeybees, though they are not native to the United States. Some research has been done on native managed species, including bumblebees and orchard bees, because, like honeybees, their populations are easy to manipulate so that their individual behaviors can be studied. The 2006 publication of the honeybee genome gave researchers another reason to focus their pollinator research on A. mellifera: sequencing the honeybee genome helped scientists understand complex biological processes that had evolved over millions of years. Christina Grozinger, director of the Center for Pollinator Research at Penn State University, explains, “There are a lot of really specific questions that you can ask with [honeybees]. You can do more-detailed experiments and more correlational research with honeybees than other bee species that are not as well understood or easy to rear. It’s a model system that you can work with really well.”

Honeybees are also studied extensively because of their ubiquity in agriculture. In the United States alone, more than 150 food crops require pollinators to produce fruits, seeds, and nuts; pollinators contribute up to $577 billion to annual global food production. Honeybees are the preferred pollinators because their hives can be transported between and set into agricultural fields and orchards.

While honeybees remain in the spotlight, they cannot do the job of pollination alone. Hummingbirds, bats, moths, flies, and thousands of other creatures make up the motley crew of pollinators that allow for effective and stable pollination. Diversity is more important than abundance of a single species, even a managed species like the honeybee. In fact, a 2016 meta-analysis reviewed thirty-nine studies and found that insects other than bees were also efficient pollinators, providing more than two-thirds of visits to crop flowers. Compared to honeybees, nonbee p...