Colony collapse: Can native pollinators take up the slack?
Although it's easy to truck in millions of honeybees to pollinate farm crops, insects originally imported from Europe are not the only game in town. Bats, butterflies, and many of the world's 20,000 bee species can also pollinate, but many questions remain about their biology and potential, says Claire Kremen of the University of California. "We know a lot less about these bees than about honeybees, but they are important pollinators for crops and wild plants."
Recent research shows that native bees can handle some of the pollination burden -- in some crops in some locations.
Jennifer Hopwood, a pollinator specialist with Xerces, notes that between 250 and 750 individual blue orchard bees can pollinate an acre of apples, a job that might require 10,000 to 25,000 honeybees. "Honeybees work a short day, but native pollinators work as long as it's light," she adds, even in the cool, damp weather that honeybees dislike.
Much of the research into native pollinators
took place in California:
organic farms near natural habitat get all pollination from natives 3;
the pollinator-dependent watermelon can subsist with native-bee pollination when at least 30 percent of the habitat is natural within 1 kilometer of the field;
but the Central Valley, with its huge farms and scarce natural habitat, do not support native pollinators, says Hannah Gaines, a post-doctoral fellow in entomology at the University of Wisconsin-Madison who studied native pollinators in California.
Further east, smaller farms and a diversified landscape are more favorable to native pollinators, Gaines says. Her research on 30 Wisconsin cranberry farms discovered five farms that did not need to rent honeybees, even though cranberries require insect pollination. Gaines is now measuring how much of pollination the natives are actually performing -- the five farms may be getting some pollination from honeybees rented by neighboring farms.
Documenting help from the wild bees
In diverse landscapes, some large farms do not need honeybees, says Mace Vaughn of the Xerces Society. "In southern Pennsylvania, one producer manages 1,000 acres of apples without renting a single honeybee colony. The orchard is spread out in diverse, old fields, with pond edges and forest, and that adds up to enough bees to do the pollination."
In New Jersey, Gaines says research she performed with Kremen 4showed that native pollinators are handling a considerable portion of pollination. "In New Jersey, 90 percent of the farms were getting 100 percent pollination for watermelon from the native bees."
Why, in contrast to reports from California and Wisconsin, did native-bee activity not correlate to on-farm pesticide use or nearby land cover? "New Jersey had organic and conventional farms, but the differences between them were nowhere like what we see in California," says Gaines. "There are some huge organic farms, and even conventional farms were growing many varieties of crops."
The smaller fields and more diverse landscape made alternate habitat available to bees on both types of farm.
Promoting pollinator habitat
Pollinator health is a key concern to apple growers, and in Wisconsin, a collaboration now called Eco-Fruit is attempting to reduce damage to pollinators -- native and rented alike - by cutting the use of fungicides and insecticides.
Because many of the growers sell directly to consumers, who tend to be leery of food with traces of synthetic chemicals, these reductions could produce a marketing advantage as well.
Since the University of Wisconsin-Madison Center for Integrated Agriculture Systems started Eco-Apple in 2000, the project has established networks of fruit growers and linked them with a "coach" who is expert in integrated pest management.
According to the Center's Regina Hirsch, about 60 orchards around the state have joined Eco-Fruit.
Integrated pest management uses field and weather data to drive pest-control decisions. Instead of just spraying chemicals on schedule ("if this is May 1, it must be time to spray"), growers check conditions. They look at weather data and forecasts to determine the probability of apple scab, the worst fungal disease, then spray fungicide accordingly. They check insect traps to find out which bugs are where in their orchards, thus avoiding needless sprays.
Data on total toxicity to people and the environment show a reduction in pesticide harm, says Hirsch. "Within three years of starting the program, growers have reduced total pesticide toxicity by almost 50 percent."
Faced with a decline in honeybees, the fruit growers are thinking about bolstering native bees. But bees, like seahorses, anacondas and hummingbirds, need to eat regularly, so now that they are using less pesticide, members of the Eco-Fruit networks are pondering planting refuges of flowering plants to feed native pollinators when the fruit crops are not blooming.
Restoring the landscape
Establishing a landscape that's more friendly to native bees may simply require "leaving things a little less tidy, with more weeds, or cheap cover crops, or planting flowers, ideally in places without pesticide drift," says Vaughn. He adds that it's not always necessary to take land out of production, as pollinator refuges can occupy stream banks, field borders and roadsides.
The ideal refuge contains a range of species that flower at different times, to ensure a steady diet for our invertebrate friends.
The Xerces Society, which promotes invertebrates conservation, offers guidelines for roadside insect refuges, which should promote pollination and foster beneficial insects that can control crop pests, Vaughn says.
At this point, despite the fact that about pollinated crops are worth about $14 billion dollars annually to American agriculture, the pollinator crisis has not caused definable economic damage, aside from the fact that beehive rental prices have roughly doubled in the past few years.
As interest in native pollinators has grown, researchers have seen them suffering from some of the same problems as honeybees. Insecticides, obviously, can kill both types of bees, and the same viruses may affect both, says Kremen. "We know a lot less about the role of diseases and problems of decline in wild bee species, but there is mounting evidence of such declines."
One step that would help all bees would be to find farming techniques that are less reliant on chemicals, or at least to reduce or replace the most dangerous chemicals, Kremen says. But chemicals are only one part of the total habitat issue, she adds. "All we have to do is provide for their habitat needs."
"There are situations where native bees can do a bang-up job on their own," says Phil Pelitteri, an entomologist at the University of Wisconsin-Madison. "The native pollinators are a much bigger pool than most people think; there are almost 4,000 species of bees in North America; most are solitary bees that live as individuals in the ground, or in the equivalent of hollow straws. But they are not bees you can truck to a farm field, and they have been suffering from habitat loss.
"You can't have native pollinators when you have a bunch of parking lots," says Pelitteri. "You have to promote patches of native ground, flowers, so they have a nectar and pollen source, and habitat to nest in the ground."
Terry Devitt, editor; S.V. Medaris, designer/illustrator; Jenny Seifert, project assistant; David Tenenbaum, feature writer; Amy Toburen, content development executive