Bumblebees Get Lost Due to Pesticide Exposure

Insecticides Cause Honeybee Memory Loss

By Susan Fluegel, PHD

Take home message: Low dose exposure to common pesticides can cause bumblebees to lose their way home. This may be due to memory loss.

Commonly used pesticides can impair the survival rate of social bumblebee colonies. Social bumblebees are bees that live and work together in a small hive.

Gill et al. (2012) reported that social bumblebees chronically exposed to two pesticides (neonicotinoid Imidacloprid and pyrethroid λ-cyhalothrin) showed impaired natural foraging behavior and increased worker mortality. Both these pesticides are frequently encountered when bees forage on flowering crops.

Bumble bees were exposed to the pesticides at low concentrations approximating field-level exposure. The research exposure mimicked the natural dose of pesticides that bees would normally be exposed to while foraging in fields and flowers for pollen and nectar.

Forty bumblebee colonies received four-week exposure to the pesticides. Bees exposed to imidacloprid foraged less effectively and collected less pollen. Due to this treated colonies had less food available and could not feed or raise as many new workers.

In addition, more bees exposed to imidacloprid got lost after leaving the colony. Bumblebees exposed to pesticides were 55% more likely to not be able to find their way home. Between lost bees, less food and fewer workers; bumblebee colonies were more likely to fail.

Pesticides Cause Memory Loss in Honeybees

In two related studies, honeybees were exposed to a combination of neonicotinoid insecticides, used to control insect pests, and coumaphos pesticides, used in honeybee hives to kill the Varroa mite, a parasitic mite that attacks the honeybee (Palmer et al. 2013, Williamson and Wright 2013). Concentrations of the pesticides in the study were similar to concentrations that bees would naturally encounter in the environment. Researchers found that both of these pesticides targeted the learning area of the bee's brain. Exposure to neonicotinoid and coumaphos pesticides caused learning disorders in the bees (Palmer et al. 2013).

When honeybees were exposed to combinations of these two pesticides for 4 days, 30% of honeybees either failed to learn or performed poorly in memory tests (Williamson and Wright 2013). Bees need to remember where food can be found and how to find their way back to the hive. They also need to know how to communicate that information to other hive members. Bees who cannot learn cannot survive and find pollen. These pesticides impair the ability of the bees to function and the ability of the hive to survive.

Read more on this topic: pesticide exposure prevents bumblebees from gathering pollen.

To help the bumblebees find their way home follow the tips on the honeybee colony collapse page.

Native Bee Facts:

Native bees and bumblebees are important pollinators for many flowering plants and some food crops.

There are over 4,000 native species of bees in the United States and Canada. There are 49 species of bumblebees in the United States.

Bumblebees can carry up to 75% up of their weight in pollen. The average bumblebee carries 25% of its weight in pollen back to the hive. That is like a 140 pound person carrying a 35 pound sack around. Makes your backpack or purse seem light doesn't it!

Do you want to know more about the plight of the bees? Check out these great free resources:

Honey Bees and Pesticides: State of the Science. By Heather Pilatic, PHD. 2012 (22 page PDF report on the factors behind colony collapse disorder that you can read or download for free at PAN North America)

A Review of Research into the Effects of Neonicotinoid Insecticides on Bees, with Recommendations for Action By Jennifer Hopwood, Mace Vaughan, Matthew Shepherd, David Biddinger, Eric Mader, Scott Hoffman Black, and Celeste Mazzacano. 2012. (44 page PDF copy available or the 2 page summary at the Xerces Society that you can download or read for free)

 

What About Birds?

Neonicotinoid pesticides kill more than bees, they are also dangerous for songbirds and aquatic systems. A report commissioned by American Bird Conservancy (ABC) stated that one corn kernel or wheat seed treated with the neonicotinoid insecticide Imidacloprid can kill an average sized songbird. A tenth of that amount can affect a songbird's reproductive ability.

For more information see ABC's report, "The Impact of the Nation's Most Widely Used Pesticide on Birds" American Bird Conservatory March 2013 by Dr. Pierre Mineau and Cynthia Palmer.

References:

Gill RJ, Ramos-Rodriguez O, Raine NE. Combined pesticide exposure severely affects individual- and colony-level traits in bees. Nature, 2012;491:105-8. Pubmed. doi: 10.1038/nature11585 (full text)

Palmer MJ, Moffat C, Saranzewa N, Harvey J, Wright GA, Connolly CN. Cholinergic pesticides cause mushroom body neuronal inactivation in honeybees. Nature Communications, 2013;4:1634. Pubmed. doi: 10.1038/ncomms2648 (full text)

Williamson SM, Wright GA. Exposure to multiple cholinergic pesticides impairs olfactory learning and memory in honeybees. Journal of Experimental Biology, 2013;216:1799-807. Pubmed. doi: 10.1242/jeb.083931 (full text)