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. Wild Insects Can Be Key To Crop Success

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by Charles Choi
New York (UPI) Apr 06, 2004
Protecting the diversity of wild insects may prove crucial in ensuring and augmenting crop yields, according to new ecological research.

"The take-home message is we have documented that wild ecosystems and their populations can provide us with important services with crops," said lead researcher Claire Kremen, a conservation biologist at Princeton University in New Jersey.

Insects are required for the spread of pollen by 67 percent of flowering plants, or 240,000 species, she said. This sharing of pollen fertilizes plants and leads to fruit and seed production.

"They fuel the entire terrestrial food chain and are critical to agriculture," Kremen told United Press International.

About 80 percent of the food crops worldwide depend on animal pollination, nearly all of which are insects. Insect pollination is worth $40 billion annually in the United States. Pollinators influence one out of every three mouthfuls of food Americans eat and all the beverages they drink, according to the North American Pollinator Protection Campaign in San Francisco.

A great deal of pollination is managed. In the United States, the business is worth $5 billion a year and 4.3 billion euros in the European Union, Kremen said.

"The continuous output and high productivity of our agricultural systems is predicated on stability, and we've seen failures or shortages of particular crops because of shortages of pollinators leading to instabilities," said Sacha Spector, manager of the American Museum of Natural History's Center for Biodiversity and Conservation's invertebrate conservation program in New York.

For instance, this year the California almond industry -- representing 80 percent of a $1.2 billion market -- was challenged by a shortage of pollinators, Kremen said.

"The acreage of almonds under cultivation has increased by 35 percent in the last 10 years," she said. "The problem is, 10 years ago California was already getting all of the 1 million bee colonies around the country and Canada to supply the state. And almond is one plant that you have to have a pollinator for, so with the expansion of acreage, there weren't enough bees to go around, and some almond orchards couldn't rent them."

The researchers studied the agricultural services provided by wild, native pollinators.

"Documenting their value is vitally important both to develop the economic case for conservation and to plan for the management of ecosystem services," Kremen said.

Kremen and her team studied 30 watermelon farm sites in California over several years, as well as 30 sunflower and roughly 10 tomato sites. About 50 different bee species pollinate those crops, she said.

To measure how efficient bees were at pollinating a crop, the scientists put bags around flowers until they opened and let bees visit them one at a time. They counted either the number of pollen grains on each bee or the number of seeds resulting from a visited flower, depending on the crop. The researchers also measured how abundant each species was on each farm. The combined figures allowed investigators to figure out the total amount of native pollinations received on each farm.

Watermelon flowers require about 1,000 pollen grains each for a marketable fruit. The researchers calculated that 80 percent of watermelon farms near wild habitats got enough pollination from native bees alone. However, only 50 percent of organic farms located far from wild habitats got enough native pollination to sustain them. None of the conventional watermelon farms far from wild habitats attracted enough native bees. No conventional watermelon farm studied was near a wild habitat.

Kremen's team found the population of native species that were most efficient at pollinating watermelon dropped off as agricultural activities intensified in terms of pesticide use, destruction of natural habitat and manipulation of the soil. These findings held true with watermelon, sunflower and tomato farms.

"She's showing you get a huge economic benefit from farming a landscape that sustains a wide variety of species rather than farming a monoculture far away from any kind of natural area," Spector said. "She's demonstrating really clear ties between our food supply and the economics of agriculture with the importance of native pollinators and biodiversity-rich landscapes."

Based on the findings, native pollinators not only save the cost of renting honeybees, but they also provide insurance against shortages of managed pollinators such as honeybees.

"If you look forward a bit, right now honeybees have been in decline for 50 years. We have 50 percent (fewer) honeybees than 50 years ago, and that trend seems to be continuing," Kremen said. "It's partly due to diseases that wiped out colonies, and also fewer young beekeepers to take up the trade. So farmers that get at least some of their pollination needs met by native bees are going to be more secure. The farmers that depend completely on honeybees will have to compete for a scarce resource."

Kremen and colleagues are now working with the Xerces Society, an international, non-profit invertebrate conservation group headquartered in Portland, Ore., on an initiative to educate farmers on how wild insects can augment crops.

"There's a big opportunity here to align our agricultural interests with invertebrate conservation," Spector told UPI. "We're seeing an increasing number of studies that show how important invertebrate conservation can be."

He said invertebrates are providing a lot of services to our agricultural systems, "like pollination, but also soil regeneration and nutrient cycling, the kinds of things that keep our agriculture humming."

"So this kind of research really shows our interest in conserving invertebrates and our interest in maintaining agricultural productivity are really the same," Spector said. "We need to get that message across and turn it into some changes in how we do agriculture."

Kremen suggested farmers restructure the landscape, "so instead of having wide, unbroken expanses of a single crop, we encourage farmers to grow multiple crops."

Although growing a single crop -- called a monoculture -- provides a burst of resources for a pollinator, it only lasts a couple of weeks until the pollen runs out.

Having multiple crops means "different things are blooming at different times," she said. "That can support a diverse community of insects -- not just pollinators, but also natural enemies that control crop pests."

She also recommended farmers use the areas they do not use for crops to grow hedgerows or flower gardens planted with native plants.

"It's important to conserve some areas of natural habitat and to restore natural habitats near farming fields," she said. "Finally, it's important to manage use of pesticides with integrated pest management strategies."

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