Honeybees, Pesticides and Colony Collapse Disorder

A European honeybee feeding on nectar
A European honeybee feeding on nectar | Source

Honeybees around the world have been dying in frightening numbers since 2006. This observation is very significant for agriculture, since honeybees not only produce honey but also pollinate flowers, allowing for fruit development. It’s been estimated that one third of agricultural crops in the United States are pollinated by bees.

There has been a great deal of speculation about the reason for the honeybee (or honey bee) decline. Suggested causes have been infections, the presence of pests, environmental changes and the use of pesticides. Some researchers feel that a combination of factors is causing the honeybee deaths. However, the evidence that pesticides are responsible for destroying bee colonies is growing.

A honeybee exploring a flower
A honeybee exploring a flower | Source

A honeybee colony contains a fertile bee called the queen. She lays eggs and is fed by the workers. Worker bees are sterile females that collect pollen and nectar and care for the colony. Male bees are called drones. Their sole function is to mate with a queen. They die soon after this job is finished.

Colony Collapse Disorder

The unexpected and unexplained death of a honeybee colony is known as colony collapse disorder. When a colony is experiencing this disorder, a strange observation is that the worker bees abandon the colony and disappear instead of dying in the hive. The living queen bee is found in the hive, as well as some young bees, but there are no worker bees present, either dead or alive. The workers have left the colony in their search for nectar and pollen and haven't returned. This is very different from the usual results when a bee colony is destroyed. Virus infections and pest invasions result in dead bees being found in and around the hive and bees of all types are killed.

A honeybee in Tanzania
A honeybee in Tanzania | Source

Neonicotinoids and Imadacloprid

A recent study from the Harvard School of Public Health claims that the most likely cause for the honeybee deaths is the use of a pesticide called imidacloprid, which belongs to a group of chemicals called neonicotinoids. These chemicals have a structure that is based on the nicotine molecule.

Bees are exposed to imidacloprid or another pesticide in the neonicotinoid family when they collect nectar from flowers or when they eat high fructose corn syrup. This syrup is often fed to bees by beekeepers. Corn in the United States is generally treated with a neonicotinoid pesticide, which contaminates the syrup made from the corn.

The Importance of Honeybees

How Does Imidacloprid Kill Insects?

Imidacloprid affects the central nervous systems of insects. It blocks the transmission of nerve impulses in nicotinergic neuronal pathways, which are very common in insects but much less common in humans and other mammals.

The word "neuron" means nerve cell. There is a small gap between one neuron and the next. When a nerve impulse reaches the end of a neuron it's transmitted via a chemical called a neurotransmitter to the next neuron. The neurotransmitter is released from the end of the first neuron, travels through the gap between the two neurons and binds to a receptor on the second neuron. When the binding takes place, a new nerve impulse is generated in the second neuron.

Acetylcholine is a common neurotransmitter and binds to both nicotinergic and muscarinic receptors. Imidacloprid also binds to nicotinergic receptors, thereby blocking the action of acetylcholine, but it can't bind to muscarinic receptors. Since insects have a lot of nicotinergic receptors, imidacloprid interferes with the action of acetylchoine in their bodies, paralyzing the insects and eventually killing them. Mammals have more muscarinic receptors than nicotinergic receptors. Imidacloprid is therefore less toxic to mammals, including humans, than to insects.

A western honeybee
A western honeybee | Source

Uses of Imidacloprid

Imidacloprid is used to protect crops and garden plants from insect pests, to control insects in homes and to control fleas on animals when applied to the back of the animal's neck. It's usually given a trade name when it's sold, so a buyer would need to check the ingredient list to see if imidacloprid is present in a product.

When imidacloprid is applied to soil, it's absorbed by the plant roots and travels throughout the plant, reaching the nectar and the pollen. Imidacloprid is said to be a "systemic" pesticide because it spreads through the plant's body. Adding pesticides to a plant so that they can kill insects throughout the growing season instead of spraying the pesticides on the insects directly is a relatively new technique. The dose of pesticide received by foraging bees is not enough to kill them immediately (a lethal dose), but is instead classified as a sublethal dose.

Genetically modified crops have sometimes been suggested as a cause of bee death. The reason why these crops may kill bees is believed to be the fact that the seeds of the plants are soaked in insecticide, which end up in the adult plant, rather than the fact that the crops are genetically modified.

The Lives of Honeybees

Effects of Neonicotinoids on Honeybee Colonies

Imidacloprid and other popular neonicotinoids such as clothianidin kill insects. Since bees are insects, the pesticides have long been suspected to be an agent in their disappearance.

In 2012, a Harvard School of Public Health study tested hives with different concentrations of imidacloprid in high fructose corn syrup, including a concentration that the researchers claim was lower than that normally encountered by bees. The researchers found that even low levels of pesticide hurt the bee populations. Death wasn't immediate, but several months after the first pesticide exposure the hives were found to be empty, apart from some young bees. The researchers didn't find any evidence of a viral infection in the hives. They also pointed out that empty hives are a characteristic feature of colony collapse disorder.

In 2014, the Harvard School of Public Health completed another study involving the effects of neonicotinoid pesticides on bees and found similar results to their first experiment. This time they also found that the colony collapse disorder was not correlated with the presence of parasites in the colony. Colonies exposed to pesticides and those that weren't contained about the same level of parasites. Only the colonies exposed to the pesticide underwent collapse.

Two drones (males) surrounded by workers (females) at the entrance of a hive
Two drones (males) surrounded by workers (females) at the entrance of a hive | Source

Other Possible Effects of Neonicotinoids on Bees

Researchers in France and the United Kingdom have also found evidence that a neonicotinoid pesticide affects bees. The French scientists found that the pesticide-treated bees found it more difficult to navigate back to the hive after a foraging expedition, while the British scientists found that the pesticide made bumblebee colonies less successful in producing queen bees.

Neonicotinoid pesticides may weaken the bees' immune system. Scientists working for the United States Department of Agriculture (USDA) - and other scientists - report that bees exposed to sublethal doses of imidacloprid have an increased level of a gut parasite called Nosema in their bodies. The 2014 Harvard experiment didn't find any evidence that supported this idea, however. Nosema is one of the parasites suspected of causing colony collapse disorder.

Drone larvae in their cells: the larvae on the left are younger than the ones on the right
Drone larvae in their cells: the larvae on the left are younger than the ones on the right | Source

Why are Bees Disappearing?

The chief manufacturer of imidacloprin, Bayer CropScience, strongly denies that the pesticide is dangerous. The company claims that the doses used in the 2012 Harvard experiment were unrealistically high and that the experiment was flawed. However, some researchers say that they are using doses that would be found in the environment in their experiments and that their results show that neonicotinoid exposure is detrimental to bees.

The final verdict regarding the cause of colony collapse disorder hasn't been reached, but according to the USDA the cause of the bee disappearance is probably due to a combination of factors. Pesticides may well be one of these factors and may perhaps be the major cause of the problem. The pesticides may be affecting the behaviour of the bees and/or some other aspect or aspects of their biology.

Whatever the cause - or causes - of the disappearing bees, an explanation and a solution need to be found very soon to protect the bees, our crops and our food supply.

Silence of the Bees

© 2012 Linda Crampton

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Comments 16 comments

writer20 profile image

writer20 4 years ago from Southern Nevada

I have seen honey bees on my plants probably for the last week, although it might be longer. Voted up.


teaches12345 profile image

teaches12345 4 years ago

I also hope that they find the reasons for the decrease in population. It will start to affect our society within the next few years, surely they know to what extent the pesticide is affecting the bees. Interesting read.


AliciaC profile image

AliciaC 4 years ago from British Columbia, Canada Author

Hi, Joyce. Hopefully a solution will be found for the missing bees. They are interesting animals to watch and are very useful insects. Thanks for commenting and for the vote.


AliciaC profile image

AliciaC 4 years ago from British Columbia, Canada Author

Thank you, teaches. Yes, colony collapse disorder may become a very urgent situation in the next few years if a definite cause isn't found. Research about the problem is very important.


drbj profile image

drbj 4 years ago from south Florida

It appears that this situation with honeybees is already urgent, Alicia, I have been reading about the problem for several years already. Can only hope that a swift solution for the problem is discovered and implemented before it is too late.


AliciaC profile image

AliciaC 4 years ago from British Columbia, Canada Author

Hi, drbj. Yes, I've been hearing about the problem for several years. It's a very worrying situation, because the activity of bees is so important in our lives. Thanks for the visit.


sligobay profile image

sligobay 4 years ago from east of the equator

This is an excellent and informative article. Thank you.

I read an article yesterday written by a Utah physician. Google autism and bees. The confusion of bees in not finding their way back to the hive is likened to the increased incidence of autism which is suspected to arise from the same neurotransmitter disorder. Roundup is the suspected culprit pesticide. You would understand and describe the concepts better than I. If we act to save the children, we may save the bees as well.


AliciaC profile image

AliciaC 4 years ago from British Columbia, Canada Author

Thank you for the comment, sligobay, and for the very interesting information. I will certainly be investigating the proposed relationship between pesticides and autism that you've mentioned. Anything that increases the incidence of autism in children needs to be dealt with immediately!


sligobay profile image

sligobay 4 years ago from east of the equator

Here's a link to the Perdue study of pesticide harm to bees. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC325042...


AliciaC profile image

AliciaC 4 years ago from British Columbia, Canada Author

Thanks for the link, sligobay. The article looks very interesting. I'm going to read it carefully!


Nell Rose profile image

Nell Rose 4 years ago from England

Great research, I have often wondered about the reason why something is affecting the Bees, now it looks like you are right, I noticed you mentioned someone stated that there wasn't enough of this chemical to hurt the bees, but of course even if only a tiny bit is in their food or environment it can hurt them, it only takes one to be totally allergic to it. I do remember reading somewhere that they think mobile phones can be causing the trouble too, something to do with their homing instinct, voted up and shared, amazing info, nell


AliciaC profile image

AliciaC 4 years ago from British Columbia, Canada Author

Thank you very much for the comment, the vote and the share, Nell! I appreciate them all. Yes, I've read about the claim that cell phone signals are causing colony collapse disorder, but so far most scientists are saying that this is speculation and that there's no acceptable evidence that it's true. Who knows, though - the whole situation is very puzzling as well as worrying, and many things seem possible at this point in time. I hope a definite reason for the problem is discovered very soon.


b. Malin profile image

b. Malin 4 years ago

What a Wonderful, factual Hub Alicia. The Honey Bee is so Important to our Food Chain. Last spring we had strange looking "Black Bees" and really no Honey Bees. It is worrisome...I'm wondering with the exception of this Mild Winter...whether the Extremely Cold ones that we had previously also was a problem, as well as the obvious Pesticides.


AliciaC profile image

AliciaC 4 years ago from British Columbia, Canada Author

Hi, b. Malin. Thanks for the visit and the comment. Climate changes have been suggested as a reason for the honeybee disappearance. There are lots of theories, but no general consensus as to what the cause of the honeybee loss is. The trouble is, as researchers search for answers the bees continue to disappear!


whonunuwho profile image

whonunuwho 3 years ago from United States

This is a very serious issue and one that needs to be addressed. Perhaps there is a pesticide that will not harm the bees. We should explore every avenue about this as quickly as we possibly can. Thank you. whonu


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

I agree with you, whonu. The plight of the bees is an urgent problem that needs to be solved quickly. Thank you very much for the comment.

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