How do Neonicotinoids Affect Bees?

Published on October 16th 2019
A field of corn with a neonicatinoids sign
Neonicotinoids, the famous brand of insecticides that have put bees to the forefront of everyone's minds.
However, there is still much debate as to whether or not they are responsible for the continued reduction in bee numbers across the world.
Neonicotinoids were first introduced during the 1990s as a way of protecting seeds from pests. The concept was that the toxic chemicals become embedded into the seed, and as it grows, every part of the plant becomes toxic to any foraging insects.
In trials, chemicals were tested for their efficiency in disabling the nervous and reproductive systems of insects that are pests to crops. Several of the ingredients are also nicotine-based, encouraging pests to return and increasing the chances of eradication.
When these pesticides were first used on sunflower seeds in southern Europe, beekeepers noticed massive losses in nearby colonies. It was only after this catastrophe that scientists began to look at the effects of these toxins on beneficial insects.
A bee on a sunflower
Sunflowers were the first commercial crops to contain Neonicotinoids
To prove whether a chemical is harmful or not, there has to be irrefutable evidence that it causes death. This is where the problems lie.
Dr Geoff Williams of Auburn University, Alabama, has been one of the many researchers looking into the effects of neonicotinoids on honey bees.
Lab trials give bees in Petri dishes doses of one or several chemicals. If the bee instantly dies, then a measurement can be taken of the lethal dose.
The problem is that the chemicals used do not kill bees outright and are designed to work on a deeper level. Dr Williams discovered this while testing two of the chemicals most commonly used, Thiamethoxam, and Clothianidin.
a bead bee face up on the ground
Dr William's study observed a marked reduction in the survival of queens and their colonies when introduced to one or several neonicotinoids.
When looking deeper, they discovered that all the bees that were exposed had smaller hypopharyngeal glands, leading to reduced lifespan and sperm quality. These results suggest that the true impact of these chemicals could take several generations to display.
Researchers at Guelph University have also discovered that grooming behaviour can become reduced amongst exposed colonies. Grooming behaviour is vital in the survival of colonies against Varroa destructor, a small mite which feeds on the fat bodies of bees during the larval stage.
A varroa mite under the microscope
A Varroa destructor under the microscope
The other concerning factor is that when brought into the hive, chemical residues become embedded in the wax comb, and can be absorbed by the developing larvae and honey. Tests have found residues of many pesticides in wax combs, some of which had been banned ten years previously.
British scientist Dave Goulson has written much on the subject of insects and pesticides. His research has found that the chemicals on treated seeds leak into the soil and can be drawn up by other plants, often wildflower strips that were planted to help the bees.
For these reasons, neonicotinoids became banned in the EU for crops that require pollination. These include oilseed rape, which is a popular source of honey, particularly in the UK. They are still used on wheat, soy and corn.
A bee on an oilseed rape plant
In Canada, huge losses of bee colonies have been noticed during the summer months. When examined, the regions affected correlated with the locations of soy and corn farms.
As you can see, this is a very complex issue. Farmers want crops that are not damaged by ‘pests’, but unfortunately the very insects and other wildlife that we want to protect are also affected. It is also worth noting that many neonicotinoids are combinations of chemicals and fungicides. These combinations are proving even more detrimental to bee health.
We also don’t know how long the residues of treated seeds last in the soil. So even after the ban, traces of neonicotinoids can still be found in wildflowers, hedgerows and the wax and honey of our bees. In fact, 47% of the honey entered in this year’s World Honey Awards was rejected after lab examinations found traces of chemicals.
A glass jar of honey on a table
47% of the honey entered in this year’s World Honey Awards was rejected
You may be thinking, ‘how does this affect me? I don’t keep bees!’ I hate to break it to you, but if you eat food, these are issues that will affect you.
All the tests on neonicotinoids so far have been performed on insects, not humans. Could we be absorbing it into our bodies? Thankfully, scientists in Canada have just begun looking into the disruptive endocrine chemicals in neonicotinoids and their effects on humans.
These chemicals are also found in flea powder for cats and dogs and could be rubbing off on plants in your garden.
Until the results are in, I am even more conscious of eating only organic corn and soy!

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