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The Bee Keeper

How Pesticides Can Be Safe for Bees and Frogs, and Still Kill Them

Two stories of unintended consequences.


Scientists in Florida wanted to know why frogs were disappearing from ponds. They suspected all manner of things... homeowner pesticide runoff, global warming, a new, exotic disease... anything and everything was up for grabs. What with bees and bats crashing and burning, who knew what it could be.

What they found wasn't what they were expecting, however. It turns out that the agricultural herbicide atrazine, a chemical that inhibits weeds from growing in crop fields, was washing out of the farm fields, flowing into groundwater and draining, eventually, into the ponds the frogs were disappearing from. But earlier tests had shown that atrazine didn't affect frogs if they had to live in water polluted with small amounts of the stuff. So it couldn't be that, could it?

The next level of tests discovered that the atrazine (remember, it's a plant killer) was, once in the pond water, killing the green algae bloom that always grows on top of most ponds in Florida. Well, that makes sense... but how could that harm frogs?

Well, once the algae on top is gone, sunlight is able to filter to the bottom of those ponds, and down there another algae lives, a brown algae. When sunlight is filtered by green algae on the surface the brown algae on the bottom is barely able to grow and isn't much of an issue. When there's light though... watch out!

Brown algae is the primary food source for the snails that live in these ponds. Lots of food means lots of snails. But snails have a parasite that lives part of its life in a snail, and part of its life in a frog. The parasite grows in a snail, then gets into a frog, killing or weakening the frog in the process, and allowing the parasite to produce eggs... which enter the water and continue the cycle. I think I have this right... I'm not an amphibian parisitologist, or a snail doctor, either.

Nevertheless, frogs were dying by the score because of the Unintended Consequences of an herbicide application made long ago and miles away.

I mention this example of Unintended Consequences because it is similar to another Unintended Consequence that is occurring in the food producing fields of the world that is having a direct and deadly affect on the bees I keep and the food you eat.

Plants, like animals, are plagued by all manner of pests. Bacteria, fungi, viruses, pests and predators all have some role. Everything is something else's lunch. For food crops, if the bad guys win there's no food, or at least a lot less of it. So farmers strive to protect their crops anyway they can. And, as you would imagine, as inexpensively as they can... Food production is a very, very thin margin business.

Lots of crops are attacked by fungi and bacteria. These organisms aren't all that aggressive so they need to find a plant's most vulnerable spot, and for a lot of plants that spot is the flower. Flowers are fragile and susceptible to damage from the weather, from animals eating them, and from invaders at the microscopic level. So farmers have to protect flowers... and to do that they have to spray pesticides directly on the flowers themselves. Sprays that attack and kill the invaders. Sprays that are absorbed by the flowers to protect them all during bloom.

Here's where the Unintended Consequences come in. It seems that the new generation of chemicals the farmers are using (called fungicides because they kill fungi) are very effective at handling the pests that are invading the flowers. But, they are also very effective at killing the pollen grains that are trying to fertilize the flowers so the fruit and nuts can grow. That's not good. The protective agent is actually killing the host it's supposed to protect.

But there's more. The pollen that my bees collect from these blossoms has the residue of these chemicals on and in it. Bees collect the pollen as a protein source in their diet, and in the process spread pollen amongst the flowers they are visiting and the flowers get pollinated. Well, they did... until this stuff was sprayed on them. But the collected pollen is contaminated with this stuff too, and bees eat it. And then...

The chemicals effectively kill all the micro-organisms in the bees' guts that help digest all the food bees eat. Just like when you take an antibiotic, you have digestion problems... so do the bees. In fact, they can't digest food at all. And then they feed this stuff to their young back home, and guess what? They actually starve to death, trying to eat more and more and more food that they can't digest. There's an Unintended Consequence for you.

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Kim Flottum

Kim Flottum

Kim Flottum is the editor of Bee Culture magazine.
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Bee Culture: The magazine of American beekeeping.
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