Ingested insecticide impacts bee population

20 May 2020

Today is World bee day. The purpose of the international day is to acknowledge the role of bees and other pollinators in the ecosystem. The day also marks the birth, in 1734, of Slovenia’s Anton Janša, regarded as the pioneer of beekeeping. The idea for World Bee Day was conceived in September 2014 when a member of The Slovenian Beekeeper’s Association considered the fact that every third spoonful of the world’s food relies on bees and other pollinators and that bees are increasingly endangered and almost no longer able to survive without human interventions and support.

20th May 2020

Muriel Cozier

Researchers at Penn State University, Pennsylvania, US have concluded that over the last 20 years insecticides applied to US agricultural landscapes have become significantly more toxic to honey bees when ingested. The work, published in Scientific Reports, is said to be the first to characterize the geographic patterns of insecticide toxicity to bees and reveal specific areas of the US where mitigation and conservation efforts could be focused.

The research team integrated several public databases, including insecticide use data from the US Geological Survey, toxicity data from the Environmental Protection Agency and crop acreage data from the US Department of Agriculture, to generate county-level annual estimates of honey bee ‘toxic-load’ for insecticides applied between 1997 and 2012. The research team defined toxic-load as the number of lethal doses to bees from all insecticides applied to crop land in each county.

The team found that the pounds of insecticides applied decreased in most counties in the period investigated, but contact-based bee toxic-load remained relatively steady. In contrast, oral-based bee toxic-load increased nine-fold, on average, across the US.

‘This dramatic increase in oral-based toxic-load is connected to a shift toward widespread use of neonicotinoid insecticides, which are unusually toxic to bees when they are ingested,’ said Maggie Douglas, assistant professor of environmental studies, Dickinson College, and former post doctoral fellow Penn State. Neonicotinoids are commonly used as seed coatings in crops such as corn and soybean. Some of the insecticide is taken up by the growing plant and distributed through the tissue.

Christina Grozinger, Distinguished Professor of Entomology and director of the Center for Pollinator Research, Penn State added ‘It is important to note that the calculation of bee toxic-load provides information about the total toxicity of insecticides applied to a landscape. It does not calculate how much of that insecticide actually comes in contact with bees, or how long the insecticide lasts before is broken down. Future studies are needed to determine how toxic load associates with changes in populations of bees and other insects.’

Scientific Reports DOI: 10.1038/s41598-019-57225-w

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