Stung by success: Intensive farming may suppress pollin...( species and we haven't developed other...)

The researchers spent two years examining watermelon farms located at varying distances from oak woodlands and chaparral habitats that are native to the Sacramento Valley. They also looked at land that was farmed conventionally (with pesticides) and organically (without pesticides). They focused on watermelon because it requires a lot of pollen and multiple bee visits to produce marketable fruit.

The research required painstaking work. Kremen and Williams first put fine mesh bags on watermelon flower buds, so that when the flowers opened they had no pollen. They then removed the bags, put the freshly opened flowers on the ends of sticks and presented them in front of bees to tempt them to land. For each of about 20 species of native bees that frequented the flowers, they determined the median number of pollen grains deposited in each visit.

Then, in each of their selected locations, the researchers watched watermelon flowers over long periods and recorded how many of each kind of bee visited. They found that native bee visits dropped off dramatically in the farms that were distant from natural habitats and that used pesticides. "We could then multiply the number of visits by the number of grains deposited per visit and sum that up for all the species and figure out how much pollen the watermelon plants were receiving," said Kremen.

"We found that, where it still flourished, the native bee community could be sufficient to provide the pollination service for the watermelon," Kremen said, adding that the result is likely to apply to a variety of other species. Farmers began renting bees many years ago to improve yields and became dependent on them as the size and concentration of farms increased. Typically, farmers whose lands are located near natural habitat don't bother to rent bees, presumably because they receive sufficient pollination from the
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9-Dec-2002