Issue 14, August 13, 2012

Neonicotinoids and Bee Reduction

There is worldwide concern about the loss of pollinators during the last few years. Colony Collapse Disorder (CCD) in honey bees has been present since at least 2006 in which large numbers of bees abandoned their hives. There has been a large decline in bumble bees noticed in California and elsewhere with a possibility of the extinction of one or more species.

Honey bee worker.

These reductions appear to be caused by a variety of stresses making the bees less capable of fending off diseases and other factors. Insecticides have always been a suspected culprit in these declines with neonicotinoids being of prime concern. Some neonicotinoids have widespread use and their systemic activity within the plant can result in their presence in pollen and nectar.

One neonicotinoid, imidacloprid, has been heavily implicated. It is known that imidacloprid is incorporated into the pollen and nectar of some plants, but not others. A French study several years ago found that honey bees exposed to sublethal dosages of imidacloprid frequently were unable to find their way back to their colony. Although successfully repeated at least once in Europe, similar studies in the U.S. were unable to repeat these results, making the research suspect. Clothianidin, another neonicotinoid, has also been implicated in bee losses.

Honey bees do not return to their hives for a number of reasons. Obviously, those who are caught and eaten by predators do not return to their hives. However, individuals that have diseases or parasites will leave the hive and not return. This behavior reduces the likelihood of the disease or parasite spreading through and eliminating the hive. It also makes it difficult to locate the involved bees and determine the cause of the abandonment.

Two new studies in Europe published in the digital version of the journal Science in March 2012 produce additional concern about neonicotinoid insecticides and bees. The journal Science is one of the most highly regarded journals in the world. These two studies utilized high quality methodology and analysis, making them more likely to be repeatable.

One study addresses imidacloprid and bumblebees in Great Britain ("Neonicotinoid Pesticide Reduces Bumble Bee Colony Growth and Queen Production." By Penelope R. Whitehorn, Stephanie O'Connor, Felix L. Wackers, Dave Goulson. Science, Vol. 335 No. 6076, March 30, 2012). Pollen and sugar water containing a nonfatal dose of imidacloprid was fed to 50 bumblebee colonies, Bombus terrestris, for two weeks. They were then released to forage outdoors. At the end of the season, the colonies were 8-12% smaller than the 25 control colonies that were not fed any imidacloprid.

The colonies receiving the imidacloprid produced, on average, about two queens per colony. The untreated colonies averaged 14 queens per colony. Bumblebees produce annual colonies, the workers and original queen die at the end of the growing season. New colonies are started each year by overwintering queens produced the previous year. Many overwintering queens die during the winter and also in the early spring when they are starting their new colonies. Mortality due to disease, predation from mammals and birds, and starvation from insufficient pollen and nectar sources are common. A reduction in queen production translates into a reduction in potential colonies the following year.

Previous laboratory and field studies have not shown a reduction in bumblebee queen production. The hypothesis is that neonicotinoids may affect bees' memory. It is postulated that foraging bees exposed to neonicotinoids forget how to get back to their colonies. Even a relatively small percentage increase in bees not returning to the colony may result in a reduction of available food to develop new queens.

The other research study was conducted in France ("A Common Pesticide Decreases Foraging Success and Survival in Honey Bees." By Mickaël Henry, Maxime Beguin, Fabrice Requier, Orianne Rollin, Jean‐François Odoux, Pierrick Aupinel, Jean Aptel, Sylvie Tchamitchian, Axel Decourtye. Science, Vol. 335 No. 6076, March 30, 2012). In this study, 600 honey bees were fitted with electronic identifiers that allowed them to be counted electronically when they returned to the hive. The bees were fed a mixture of sugar water containing low doses of thiamethoxam, another neonicotinoid insecticide. The doses used were determined to be similar to those that the bees would be exposed to in nature.

The bees were then released up to one kilometer (0.6 miles) from the hive. The bees were released in areas where they had been previously as well as in areas that were new to them. Only about one-half of the bees dosed with thiamethoxam returned to the hive compared with those that did not receive any insecticide. This translates into less food, pollen and nectar, coming back to the hives resulting in weaker hives.

One concern is that the insecticide doses were administered all at once rather than smaller doses repeated throughout the day as is more likely in nature.

The source for much of the above was obtained from news articles posted on The Xerces Society web site. The Xerces Society is a nonprofit organization that protects wildlife through the conservation of invertebrates and their habitat. Those articles can be found on The Xerces Society web site.

Although these two studies appear to indicate that neonicotinoid insecticides might be responsible for pollinator reductions, there are other research studies that indicate the opposite. Additional research has pointed at one or more other factors. Insecticide use may be one of the stresses causing colony collapse disorder and other pollinator reductions, but these reductions are apparently due to a number of factors. (Phil Nixon)

Phil Nixon

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