NewScientist‘s Stephanie Pain (25 April 2015) reports on the recent discovery that plant nectar often contains toxins (paywall):
At least 15 genera of plants contain caffeine, primarily as a chemical defence against insects, or so it was thought. Caffeine tastes bitter to insects, and bees are no exception; they find it repellent. But this doesn’t deter them from visiting the flowers of coffee and citrus plants, the nectar of which has been found to contain caffeine. It turns out that the caffeine is present at levels too low for bees to taste, as Stevenson and neurophysiologist Jeri Wright at the University of Newcastle, UK, recently revealed. Yet when offered a choice of nectar with or without a dash of caffeine, bees prefer it with. Wright suspected that caffeine acts as a drug, influencing a bee’s mind in much the same way it does ours. She was right.
In the lab, Wright trained bees to associate nectar with a particular floral scent. When she added caffeine to a drop of nectar, twice as many bees remembered the scent three days later. Closer investigation suggests that caffeine produces this dramatic improvement in long-term memory by intensifying how the bee’s brain reacts to information from its antennae, where smells are detected (Science, vol 339, p 1202).
If bees remember which scent or colour indicates good food, they are more likely to return to the same sort of flowers, bringing other members of the colony with them. Plants that use caffeine to manipulate bees’ minds in this way should benefit from the greater loyalty of their pollinators.
A single toxin may affect different pollinators differently, tests show:
Tests with captive bees showed that grayanotoxins have dramatically different effects on different types of bee. “They have no apparent effect on worker bumblebees,” says Stout. “Mining bees show short-term symptoms of malaise. They lie on their backs with their legs in the air but recover later. But honeybees die within hours.” In honeybees – and humans – grayanotoxins hold open the sodium channels present in all nerve and muscle cells, so that neurons keep firing until they are fatigued. In the bees, this leads to palpitations, paralysis and death. “We don’t know why this doesn’t happen in bumblebees,” says Wright. “Like any other drug, some animals are more susceptible than others.”
So what does this have to do with monoculture? From the accompanying sidebar:
Toxic nectar is more of a threat in landscapes where a single crop or invasive plant that produces nasty nectar covers vast areas. Then, a pollinator’s options are limited. “If bees feed on toxic nectar, they might be poisoned. If they avoid it but there’s little else around, then they’ll suffer from inadequate nutrition. Either way, that could have a severe impact on their colony,” says Stevenson.
So, how to avoid adding to pollinators’ many problems? “We can try to manage the landscape in ways that make it better for pollinators,” says Stevenson. “The most obvious way is to ensure there is a wide enough choice of flowers to satisfy the needs of a diversity of bees and other pollinators.”
If you’re wondering about monoculture, SustainaBlog gives a brief economic theory behind it and tries to define rename it:
One of the most wise and basic farming practices is to “rotate crops.” If a farmer plants a grass crop one year, a broadleaf crop the next, a different grass the next, etc. it tends to break pest cycles and to put different nutritional pressures on the soil. Actually, most of what people imagine as “Big Ag” or “Industrial Farming” actually involves rotated crops on family farms. The rotation differs by geography. In the heart of the Corn Belt there is usually a soybean/corn rotation with winter wheat in some areas. In the Southeast, cotton, peanuts and wheat tend to be mixed in with the corn and soy rotation. North and West of the Corn Belt wheat, sunflowers, sugar beets, canola are common rotation options. These traditional rotations are employed on hundreds of millions of acres of US farmland. …
If someone is serious about a critique of modern agriculture, “monoculture” is not the best term to use – particularly if you want to communicate with farmers. The real issue is the difference between “diverse rotations” and “non-diverse rotations.”
