Honeybee Disappearance: Pesticides and Colony Collapse Disorder

Updated on July 13, 2018
AliciaC profile image

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about animals and plants.

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

The Death of Honeybees

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 decline. Suggested causes have included 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. The evidence that pesticides are at least partly responsible for killing bees 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

Researchers at the Harvard School of Public Health think that the most likely cause of honeybee deaths in colony collapse disorder is the use of a pesticide called imidacloprid. This belongs to a group of chemicals feferred to as neonicotinoids. The 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.

How May Imidacloprid Harm 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 an excitatory 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. if the dose is high enough, the insects may be paralyzed by the pesticide and eventually die. 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.

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.

The chief manufacturer of imidacloprid, 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.

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

Even sublethal doses of pesticides may be harmful for 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

In 2017, the results of four large-scale research projects were published. A Canadian experiment and three European ones studied the effect of a neonicotinoid on honeybees. Two of the experiments clearly support the idea that the neonicotinoid is harming bees. A third provides weaker support. The fourth provides no support.

A Canadian Experiment

A research team from York University in Toronto studied honeybee colonies close to cornfields as well as colonies so far away from the fields that they would never have visited them. According to one scientist from the university, almost all corn is treated with neonicotinoids. The team collected samples of pollen and nectar from the hives every few weeks.

The researchers found neonicotinoids in the hive samples collected near the cornfields. The most abundant kind was clothianidin. Interestingly, the scientists found that the contaminated product collected by the bees came mostly from flowers around the cornfields rather than from the field itself.

The team then fed some test bees pollen containing the same concentration of clothianidin discovered in the first part of the experiment. Other bees were given uncontaminated pollen. The researchers also attached tracking devices to the bees. The bees given the contaminated pollen had a 23% shorter lifespan and took up to 45 minutes longer to return to the hive after a foraging expedition. The researchers speculate that the bees were having trouble remembering where their hive was. The contaminated bees also took longer to remove sick bees from the hive.

The European Experiments

A team of European researchers placed some bees near a field of rapeseed plants that had been treated with clothianidin. (Rapeseed or oilseed rape plants are grown for their oil-rich seeds.) The researchers placed other bees far away from the plants. The experiment was performed in three countries. After the winter, around 24% of the test bees in Hungary had died. The test bee population in Britain decreased as well, though to a lesser extent. Unexpectedly, the population of test bees in Germany wasn't harmed and even increased.

The scientists discovered that food from rapeseed fields formed 15% of the diet of the German bees. It formed 40-50% of the diet of the Hungarian and British bees. The lower percentage may have enabled the German bees to survive. The bees may also have been healthier at the start of the experiment or may have had genetic resistance to the pesticide. It's also possible that other components of their diet gave them resistance.

In October 2017, Swiss scientists reported their analysis of honey sold to humans in different countries. Overall, 75% of the 198 samples contained a measurable amount of neonicotinoids. The percentage of contaminated North American honey was 86% (the highest result).

2018 Research and a New Regulation

In 2018, scientists published their analysis of research related to the effects of pesticides (neonicotinoids and other types) on honeybee and bumblebee memory. Researchers from the Royal Holland University of London looked at 23 studies involving a total of 100 experiments. The studies showed that whether the bees were exposed to a high dose of pesticide at one time or a small dose repeated over a long time, their memory was impaired.

On May 30th, 2018, the European Union banned the use of imidacloprid, clothianidin, and thiamethoxam outdoors. The pesticides may only be used inside permanent greenhouses. The Union considers another neonicotinoid—acetamiprid—to be of low risk to bees. This pesticide may still be used outdoors.

Why Are Bees Disappearing?

The final verdict regarding the cause of colony collapse disorder or a general decrease in bee population hasn't been reached. According to the USDA, the cause of the bee disappearance is probably due to a combination of factors. Some other researchers agree with this assessment. Many scientists believe that pesticides are likely at least one of the factors affecting the bees. 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 honeybees, an explanation and a solution need to be found very soon to protect the bees, our crops, and our food supply.


Neonicotinoids and colony collapse from the Harvard School of Public Health

Bees and pesticide information from the EPA (Environmental Protection Agency)

Information about honeybee health and colony collapse disorder from the USDA

Imidacloprid facts from the National Pesticide Information Center

Canadian and European research from Scientific American

Pesticides can sometimes kill bees from Science (an American Association for the Advancement of Science Publication)

Honey contaminated by pesticides from The Guardian

Pesticides and bee memory from Popular Science

Causes of colony collapse disorder from The Conversation

Neonicotinoids from the European Commission

© 2012 Linda Crampton


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    • AliciaC profile imageAUTHOR

      Linda Crampton 

      6 years ago from British Columbia, Canada

      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.

    • whonunuwho profile image


      6 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 imageAUTHOR

      Linda Crampton 

      7 years ago from British Columbia, Canada

      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!

    • b. Malin profile image

      b. Malin 

      7 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 imageAUTHOR

      Linda Crampton 

      7 years ago from British Columbia, Canada

      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.

    • Nell Rose profile image

      Nell Rose 

      7 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 imageAUTHOR

      Linda Crampton 

      7 years ago from British Columbia, Canada

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

    • sligobay profile image


      7 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 imageAUTHOR

      Linda Crampton 

      7 years ago from British Columbia, Canada

      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


      7 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 imageAUTHOR

      Linda Crampton 

      7 years ago from British Columbia, Canada

      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.

    • drbj profile image

      drbj and sherry 

      7 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 imageAUTHOR

      Linda Crampton 

      7 years ago from British Columbia, Canada

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      7 years ago from British Columbia, Canada

      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.

    • teaches12345 profile image

      Dianna Mendez 

      7 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.

    • writer20 profile image

      Joyce Haragsim 

      7 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.


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