Fungicides and Bees: Part One

Bee on Phacilia forage two MBFI tour Aug 2017

Image: Angela Lovell

In this three-part series we take a look at the negative health effects of fungicides on bees, what farmers can do to minimize the risks and what other producers are doing as an alternative to using fungicides.

Part one: Fungicides could be having negative health impact on bees.

A team of scientists at Cornell University studying pollinator health were surprised to find that fungicides could be having negative health impacts on wild and managed bee populations.

There has been a lot of research studying the effect of insecticides, such as neonicotinoids, on bee health, but it was largely assumed that fungicides, designed to kill pathogens, had no impact on bees. Although researchers found that fungicides themselves are not necessarily very toxic to bees, they can act synergistically with insecticides to make them much more toxic to bees.

Fungicides and insecticides together are more toxic to bees

Fungicides can do two things, says Scott McArt, assistant professor of entomology at Cornell University’s College of Agriculture and Life Sciences, who led the research. “In our laboratory we have shown that fungicides can synergize with insecticides and causes the detoxification mechanism in the bees to be knocked out so they are unable to detoxify the insecticide as well, and even at low levels the insecticide then becomes much more toxic to the bee,” he says.  In their tests the rate of death of bees increased by a least 25 per cent when they were exposed to fungicides and insecticides as opposed to just insecticides alone.

Secondly, in their analysis of bumblebees in the United States, researchers have found that fungicides interfere with the bee’s gut microbiota. “Just as humans need a good balance of microbiota in our gut for proper function, so do bees,” says McArt. “If the fungicide impacts the microbiota the bee is more susceptible to pathogens, in particular nosema, which is a gut pathogen specific to bumble and honeybees.”

In the team’s analysis of 198 managed bee colonies across New York State they found that each had at least six different detectable pesticides in the hives, and 90 per cent of the residues found were fungicides. Overall, their lab research found that fungicides are the best predictor of range contractions in wild bees. “We are not sure if fungicides are contributing to bee decline, but we know that there is a connection between fungicides and the disappearance of bees from areas where they were previously present,” says McArt.

Chlorothalonil of particular concern

One of the active ingredients in some common fungicides – chlorothalonil – has been shown to be especially harmful because it synergizes particularly well with common insecticides such as neonicotinoids and pyrethroids and makes them five times more toxic to bees. “Laboratory studies have shown that exposure to chlorothalonil makes bees more susceptible to nosema,” says McArt. “Although we have to do further studies to understand why, we know it is disrupting the microbiota so they are not blocking the pathogen.  We are also hypothesizing that it could be killing actual gut cells, so there are less to ward off pathogens and less of an immune response.”

Chlorothalonil is an active ingredient in a number of fungicides registered with the Canadian Pest Management Regulatory Agency. Some of those used for agricultural purposes include Bravo 500® and Daconil® from Syngenta.

In response to an email inquiry to Syngenta asking if someone from the company could comment on this research and make any recommendations for growers, Peter Campbell, Head of Research Collaborations for Syngenta at Jealotts Hill, UK replied.

“This study is a correlative study and the authors themselves within the publication ‘caution against over-interpretation of correlational patterns between pathogens and bee declines that may not be indicative of larger patterns or causal mechanisms.’

“Among other things, this suggests a need for further research investigating the reported correlations to provide greater clarity regarding the presence or absence of a plausible mechanistic pathway of causation.”

“It is also well known that a major factor affecting bumble bee populations and their ranges is habitat, in particular, availability of nesting, foraging and queen over-wintering sites. While habitat was included as a variable in this analysis, the classification used was very broad (e.g. cropped land, forest, agricultural area). The categories used in the study are too broad to capture the specific habitat needs of different bumble bee species in terms of their nesting, feeding and queen over-wintering site preferences, as well as the need for continual availability of food.”

Not just a problem for bees

Research into pollinator health has gained a lot of momentum over the past four or five years as there has been a much broader recognition that declining pollinator populations is a serious issue that could have a huge financial impact on agriculture, not to mention global food security.

The United States typically loses 25 to 40 per cent of managed honeybee colonies every year and the last three years that rate has been between 44 and 54 per cent.  There are 416 wild bee species documented in New York State and 53 are known to have had range contractions over the last few years.

The problem is not just unique to bees. A German paper recently published showed a 75 per cent reduction in total insect biomass in Germany in the past 25 years, not restricted only to bees. “There are likely many causes but we have seen a reduction in insects over the last 30 to 40 years we have never been seen before,” says McArt. “It’s a worrying trend.”

(A version of this story first appeared in Grainews).

Next week in part two of this three-part series we explore what farmers can do to minimize risk of fungicides to bees?

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