February 28, 2013
Insect pollination is crucial for the healthy development of our favorite foods, from apples and avocados to cucumbers and onions. Of the 100 crop species that provide 90 percent of the global population’s food, nearly three-quarters rely on pollination by bees. The rest need beetles, flies, butterflies, birds and bats to act as pollinators. It’s a mutually beneficial system—the flowers of most crops require pollen from another plant of the same crop to produce seeds or fruits, and bees and other critters transfer pollen from one plant to the next as they drink a flower’s nectar.
The agriculture industry relies on both wild pollinators and human-managed ones like honeybees, kept and cared for in hives across the country. Concern over the latter’s gradual decline has grown in recent times, but new research shows it might be the wild pollinators we should be worrying about.
In a study of 600 fields of 41 major crops (fruits, grains and nuts) on six continents, published today in the journal Science, researchers found that wild insects pollinate these crops more effectively than honeybees that are in the care of humans. In fact, compared to bees living in apiaries, wild pollinators lead to twice as much of what’s called “fruit set”—the amount of flowers that develop into mature fruits or seeds.
Pollination is essential for the production of fruits like cherries, cranberries and blueberries. Blueberries, along with tomatoes, especially depend on buzz pollination, a process by which bees vibrate their flight muscles rapidly to unleash a visible cloud of pollen into a flower. Honeybees aren’t capable of this kind of pollination, says lead study author Lucas Garibaldi, a professor at the National University of Río Negro in Argentina. Of all pollinator-dependent crops, approximately 8 percent require buzz pollination, he says.
Pollination, then, is central to ensuring our both our food staples and our varied diet.“These ecosystem services are free, but they’re important for our survival,” Garibaldi adds. “They need to be promoted and maintained if we want to continue living on this planet.”
Another new study found that wild bee population, as well as the number of different species of the insects, has plummeted over the last 120 years. Researchers used observations of interactions between plants and their pollinators in Illinois collected at three points in time: in the late 1800s, the 1970s and the first decade of this century. Of the 109 bee species seen visiting 26 woodland plants in the 19th century, only 54 remained by 2010. Rising temperatures caused mismatches in peak bee activity, measured by visits to different plants, and flowering times, a break in the delicate balance of insect-plant relationship.
Less diversity in the wild bee population meant fewer interactions between flowers, a change that in the agricultural world could result in smaller crop yields, says lead author Laura Burkle, an ecology professor at Montana State University. This throws off global agriculture production and speeds up land conversion to compensate for the loss.
“Things have changed for the worst,” Burkle says. “There’s an incredible amount of robustness within these interaction networks of species that allow them to persist in the face of really strong environmental changes, both in temperature and land-use change.” Unfortunately, these pollinators are “getting punched from a variety of sides,” she adds.
Can honeybees substitute for our disappearing wild pollinators? Garibaldi and colleagues found that these insects couldn’t fully replace the contributions of diverse populations of pollinators for a wide range of crops on farmlands on every continent. Flooding farmland with human-managed honeybees only supplemented pollination by wild insects, even for crops such as almonds, whose orchards are stocked routinely with bees.
Several culprits are behind the continuing decline of these wild pollinators. The insects usually live in forests and grasslands, and continuing conversion of such natural habitats into farmland results in shrinking numbers and types of wild pollinators, meaning fewer flowers receive the pollen necessary for reproduction.
Last year, many plants in the eastern U.S. flowered a month earlier than any other time in the last 161 years, a result of such unusually warm weather. Burkle says bee development doesn’t always catch up to changing flowering times in plants, which leads to more mismatches in interaction and decreased pollination services. Another study in the same year found that elevated levels of carbon dioxide, combined with the use of nitrogen-infused fertilizer, altered some plants’ lifetime development. The toxic pairing led them to produce flowers with nectar more attractive to bumblebees than usual, but caused the plants to die sooner.
The waning insect population has already taken a measurable toll on crop production, including on one very near and dear to our hearts: coffee. A 2004 study of coffee pollination in Costa Rica found that when numbers of human-introduced honeybees shrunk in a given forest area, diverse pollinators native to the area, such as stingless bees known as meliponines native to the area, helped compensate for the loss. But these insects couldn’t survive at the edges of the forest like honeybees could, so the production of coffee, a crop highly dependent on pollination, eventually plummeted.
“This study supports the theoretical prediction that having many different species, which each respond to the environment in slightly different ways, is like having a stock portfolio from many different companies, rather than investing all your money in a single company’s stock,” explains Jason Tylianakis, a terrestrial ecology professor at the University of Canterbury in New Zealand. Tylianakis discussed the implications of Science’s two new studies in a paper also published today. “We should expect this kind of ‘insurance effect’ to become less common as more native pollinators go extinct.”
Given the mounting evidence, Tylianakis writes in an email that concerns about a global pollination crisis are not overstated. A changing climate, the rapid spread of farmland and a reliance on pesticides means diverse, wild pollinators will continue to face challenges as this century unfolds. If pollinators are dying out worldwide—and if pace of this die out continues with the variety of species getting cut in half each century, leaving behind less effective substitutes—food production as we know it could start to crumble.
“The bottom line is that we need biodiversity for our survival, and we can’t simply replace the services provided by nature with a few hand-picked species like the honeybee,” he says.
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