New research out of York University, Toronto, has added yet more weight to the growing scientific literature that neonicotinoid pesticides are a major contributor to bee colony decline, as well as a magnification effect when paired with fungicide.
The study concluded that worker and queen bees exposed to neonicotinoids had poorer hygiene and died sooner than colonies that weren’t exposed. The study was designed to test a long-running defence against previous research into neonics: that exposure trials in labs had a tendency to overexpose bees to levels of neonics that were way above what they would encounter in the field.
But Professor Amro Zayed and his team se up this trial to mimic the levels and patterns of exposure that bees would encounter in the real world. Professor Zayed said:
This debate about field realistic exposure has been going on for a long time. We needed season-long monitoring of neonics in bee colonies to determine the typical exposure scenarios that occur in the field, which we have now done.
Professor Zayed’s team monitored apiaries close to corn fields that had been seed-treated with neonics, monitoring the levels found on the bees from May to September. They also sampled apiaries far from agriculture to use as a basis of comparison.
The study found colonies close to corn fields were exposed to neonics for three to four months, almost the entire active season for bees in North America. The researchers used their field trials to set up a lab test that exposed bees to neonics with a similar dosage and pattern they would encounter in the field.
They used artificial pollen inoculated with progressively smaller amounts of the most common neonic in North America, clothianidin, so it mimicked field expose, giving them solid data to counteract the lab overexposure argument.
Their results showed a 23% decline in the lifespan of honey bees, as well as a lack of hygiene and an inability to maintain healthy queen, all of which contributed to overall decline in the healthy of bee colonies.
A surprising result for the team was the finding that the bees exposed to neonics in the field had a tendency to test positive to the pesticide, even though they didn’t collect pollen from the inoculated corn crop (which is wind-pollinated). Neonicotinoids are highly water-soluble and work their way into surrounding ecosystems readily, often finding their way into plants that bees frequent in preference to others. This was the explanation the team offered for the presence of neonics in bee colonies despite them not visiting the plants neonics were applied to.
As if that wasn’t enough, the researchers also discovered a magnification effect when neonics and fungicides are applied together. A common fungicide in North America, boscalid, was found to amplify the toxicity of neonicotinoids by 100%, effectively doubling their toxicity and effects on bees.