Script:
Listen to part of a talk in a biology class.
M: Until recently, we knew almost nothing about how important bees are in maintaining natural diversity. Now we know more about them. We know, for example, that honeybees are the dominant pollinators because they play a role in pollinating four out of five food crops in North America. We also know that honeybees along with the other insects, bats, and birds that transfer pollen between flowers—all together they contribute more than ten billion dollars a year to fruit and seed production on North American farms. Pollination is one of nature’s services to farmers. So think about this: if you eliminated the pollinators, it would take the food right out of our mouths. We biologists never imagined we′d see the day when wild plants or crops suffered from pollinator scarcity. But, unfortunately, that day has come. In fact, fanners in Mexico and the U.S. are suffering the worst pollinator crisis in history. So ... what happened? Any ideas? Alicia?
W: Is it ... um ... because of natural enemies? I read something about a kind of parasite that’s killed lots of bees.
M: It’s true. An outbreak of parasitic mites has caused a steep decline in North American populations of honeybees. But parasites aren′t the only factor.
W: What about the pesticides used on farms? All those chemicals must have an effect.
M: Most definitely, yes. Pesticides are a major factor. Both wild and domesticated bees are in serious trouble because of pesticides. In California, farm chemicals are killing around ten percent of all the honeybee colonies. Agriculture in general is part of the problem. Think about this for a minute: the North American continent is a vast collection of “nectar corridors“ made up of flowering plants. These corridors stretch for thousands of miles, from Mexico to as far north as Alaska. And every year, there′s an array of migratory pollinators flying north and south with the seasons, following the flowers. The migratory corridors the flyways—are like ... uh ... something like a path of stepping-stones for the pollinators, with each “stone” being a collection of flowering plants. But our system of large-scale agriculture has interfered. During the past fifty years, millions of acres of desert in western Mexico and the southwestern United States have been turned into chemically intensive farms, planted with exotic grasses, creating huge stretches of fly way that are devoid of nectar-producing plants for migratory pollinators. What we have now are huge gaps between the stepping-stones—patches of plants here and there. A couple of migratory pollinators are worth noting. One is the lesser long nosed bat, and another is the most famous pollinator what is our most famous pollinator? Or I should say our most beautiful pollinator.
W: Oh, I know. It’s the monarch butterfly!
M: The monarch butterfly—yes. Millions of monarchs from all over the U.S. and southern Canada fly south every year in late summer. The monarch is the only butterfly that returns to a specific site year after year. Unfortunately, the herbicides used on the milkweed in the Great Plains are taking a toll on monarchs. and fewer of them are reaching their winter grounds in Mexico. Another important pollinator is the long nosed bat. These amazing animals feed on cactus flowers. What they do is, they lap up the nectar at the bottom of the flower, and then when the bat flics off to another cactus, the pollen stuck to its head is transferred to that plants flower. But the long-nosed bat is having a tough time, too. Some desert ranchers mistake them for vampire bats, and they’ve tried to poison them, or dynamite the caves where they roost.