For related articles and more information, please visit OCA’s Genetic Engineering page, Millions Against Monsanto page and our Honey Bee Health page.

A team of scientists in Italy believe they have found the molecular mechanism through which neonicotinoid pesticides adversely impacts the immune system of honey bees. The team’s experiments suggest that exposure to neonicotinoids results in increased levels of a particular protein in bees that inhibits a key molecule involved in the immune response, making the insects more susceptible to attack by harmful viruses.

Though previous studies have indicated that exposure to minute amount of neurotoxic pesticides like neonicotinoids severely impair the immune systems of bees, making them more susceptible to pathogens, the underlying mechanism has was not yet been fully understood. The study, published in the Proceedings of the
National Academy of Sciences of the United States of America, is the latest of severalstudies to add weight to the urgency of repeated calls from U.S. beekeeper and environmental groups for the U.S. Environmental Protection Agency (EPA) to suspend the use of neonicotinoid pesticides, as the European Commission decided this past April.

Neonicotinoids, a class of insecticides that includes clothianidin and imidicloprid, are taken up by a plant’s vascular system and expressed through pollen, nectar and gutation droplets from which bees forage and drink. They are particularly dangerous because-in addition to being acutely toxic in high doses-they also result in serious sublethal effects when insects are exposed to chronic low doses, as they are through pollen and water droplets laced with the chemical, and dust that is released into the air when coated seeds are planted with automated vacuum seed planters. These effects cause significant problems for the health of individual honey bees as well as the overall health of honey bee colonies. Effects include disruptions in bee mobility, navigation, feeding behavior, foraging activity, memory and learning, and overall hive activity.

Up until now, the causal link between insecticide exposure and immune alteration has been unclear. Francesco Pennacchio, Ph.D. of the University of Naples Federico II, and his colleagues identified a gene in insects similar to that found in other animals that is known to regulate the immune response. This gene codes for a leucine-rich repeat protein family (LRR) which has been shown to suppress the activity of a key protein involved in immune signaling, called NF-κB. When the researchers exposed bees to sublethal doses of the neonicotinoid clothianidin, they saw a significant increase in the expression of the gene encoding the LRR protein, and a concomitant suppression of the NF-κB signaling pathway. These effects were not seen when bees were exposed to the organophosphate insecticide chlorpyriphos.