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'Safe' pesticides make bees more vulnerable to killer parasites

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Bee on flower (Credit: US Dept. of Agriculture/Flickr)
Bee on flower (Credit: US Dept. of Agriculture/Flickr)

The population of honey bee colonies worldwide has severely declined in recent decades, shrinking about 30 percent each year between 2007 and 2010, and scientists still aren't exactly sure what precise set of factors are to blame. The decline has included instances of colony collapse disorder, when there are suddenly very few or no adult bees in an entire colony. Whatever factors are leading to this decline, one thing is certain: it's only accelerating, and that could lead to higher food prices for all of us. Earlier this year, some US beekeepers reported bee colony losses of up to 80 percent. Now a new study from US government and university researchers has identified some new potential culprits: fungicides and miticides, popular chemicals designed to kill fungus and mites, sprayed by farmers on apple trees and bee hives themselves. Fungicides and miticides were thought to be safe for bees, but as it turns out, several types of these chemicals actually make the insects considerably more vulnerable to being infected by a killer parasite called Nosema, which has previously been linked to colony collapse.

Three-times greater risk of parasite infection

The study, which was conducted by researchers at the US Department of Agriculture (USDA) and the University of Maryland, involved collecting pollen samples from bees that regularly pollinate seven different major crops: almond, apple, blueberry, cranberry, cucumber, pumpkin, and watermelon. What the researchers found was striking: up to 35 different types of pesticides in the pollen, including heavy doses of fungicides. Bees that eat pollen coated with two types of fungicides — chlorothalonil and pyraclostrobin — were found to have a much greater risk of being infected by Nosema. Pyraclostrobin in particular increased the risk of bee infection by three times.

In other disconcerting news, the study found that a similarly increased risk of parasite infection from chemicals beekeepers regularly spray on hives to control mites. However, the authors of the study noted that one practice many beekeepers are already doing — rotating honeycombs out of hives — "will hopefully decrease spread of these chemicals to the environment." The study isn't the first to link pesticides to honey bee colony collapse, but it is the first to pinpoint these specific types of fungus and mite-killing chemicals as possible causes. "Our study highlights the need to closely look at fungicides and bee safety, as fungicides currently are considered safe and can be sprayed during the bloom on many crops," said co-author Dennis vanEngelsdorp with the University of Maryland, in a statement published by the USDA.