The dramatic decline in Honeybee populations


Matthew Canning- Natural Resource Conservation

Andrew Koval- Wildlife Conservation

Kendra McNabb- Animal Science

Bees are quite an amazing insect, they pollinate over 80% of all flowering plants including 70 of the top 100 human food crops. One in three bites of food that we eat is derived from plants pollinated by bees (Allen-Wardell et al, 1998). Needless to say, bees are important to the crops we humans consume on a daily basis. Over the past two decades, the decline in bee population has reached a critical point. The United States Environmental Protection Agency (2017) concluded that there is a 30% decrease in hive losses annually within the United States. When introduced to stressors, bees can have adverse reactions, leading to what is known as Colony Collapse Disorder (CCD). This disorder that is plaguing global bee populations causes many of the adult and working bees in a specific hive to die out, leaving the colony unable to nourish and protect offspring. This eventually leads to a full destruction of the entire hive. The most logical reason for this phenomenon is the introduction of specific stressors to the hive and its bees directly (VanEngelsdorp, Evans, Saegerman, Mullin, Haubruge, Nguyen, Brown, 2009). If something isn’t done to manage declines in bee populations we can expect a negative impact agriculturally and ecologically. Allen-Warden et al. (1998) showed insecticides and pesticides’ have adverse effects on bees and other pollinating wildlife. This study also showed a reduction in pollinators caused a decrease in blueberry production. We can expect a similar impact on crops to continue as time goes by and this issue progresses. Estimates of the economic toll of honey bee decline is upwards of $5.7 billion per year (United States Environmental Protection Agency, 2017). It is not out of the question that soon homeowners will have trouble keeping their personal gardens sufficiently pollinated, and forego that simple yet satisfying pastime. Knowledge of bee decline  has been acknowledged for many decades, but research and data behind the reasoning for the global decline are still heavily debated.

As humans, we consume a substantial amount of things. With this consumption comes waste. All of this waste, runoff and toxins needing to go somewhere are released into the surrounding environment and create pollution. This pollution has many negative effects on the ecosystem.  (Tisler et al., 2009; Krupke et al., 2012; Rundlöf et al., 2015; & Cresswell et al., 2012) . One form of pollution that could be a large contributing factor to CCD are the toxins burned polluting the atmosphere. Bees forage for and locate their food through scent and memory. With the increase in air pollution, Eilperin (2008) states that bees have lost the ability to smell a flower’s aroma by 90%. This causes the bees to fly around aimlessly in search of food, leading to starvation and death. Individual bees inability to feed can lead to CCD within a single bee population.

There are numerous suspected stressors that bees are exposed to everyday. The rapid change of their environment or surrounding climate may play a huge role in the rapid decline in bee population. Kerr et al. (2015) tested for any shift in bumblee range due to climate change in North America and Europe. In conclusion, it was found that bumblebees have not shifted northward and are experiencing shrinking distributions in the southern ends of their range. Such failure to shift suggest an elevated susceptibility to rapid climate change. With many factors such as pollution, habitat loss, and ozone depletion, our climate is shifting rapidly and changing the structure of many and most ecosystems with it (Goulson, 2013). Climate change is causing change in temperature. Bees are sensitive to temperature change and when exposed to this kind of stressor it has significantly negative affects on their survival. In an experiment, Archer, Pirk, Wright, & Nicolson (2014) simulate a change in the environment by exposing bees to temperatures of 30 degrees (below optimal temperature) and 35 degrees celsius (optimal temperature that these specific bees are acclimated to). The added temperature decrease on the bees did in fact decrease the consumption rate of proteins for each bee by approximately 25%. They consumed less proteins during 30 degree exposure than while under no stress at their usual 35 degrees. Bees inability to consume sufficient proteins and range northward during higher temperatures proves that it may be a contributing factor to CCD, but not the dominating singular cause.

There is one “thought to be” singular cause, one lone contributing factor that may have more of a dominating effect on bees then other stressors such as climate change or pollution. A hypothesis for CCD that has been drawing increased attention lately is pesticide usage. It was proposed that farmers pesticides could be killing bees, and those responsible should be liable (VanEngelsdorp, 2009).  Rundlöf et al. (2015) found that among tested crops (corn, cotton, and soybean) up to 70% of total pollen collected by honey bees can come from crops during their peak flowering times. A counter study by Botías et al. (2015) revealed that during peak flowering, honeybees collected 91.1% of their pollen from wildflowers. In the late crop flowering period, 100% of honey bee pollen was collected from wildflowers, showing that not all crop flowers are used heavily by honey bees. Available data suggests that usage of pesticides is not a major contributing factor to the decline in bee populations. With this conclusion in mind, farmers could then argue that if they have a crop not used by honey bees, they should not be responsible for its pesticide exposure. Pesticides have been around for many years, providing many benefits and protections for farmers, consumers and the exposed crops.

Pesticides are not only beneficial to the farmer. They also provide a type of insurance for the consumer. There are many public health concerns that surround the agricultural industry, specifically with how our crops and food are handled and cared for. Farmers use pesticides to control and prevent the spread of viruses and diseases. They are used for protecting the crops from insects and small animals that would consume and possibly pass on a virus or disease it was carrying (Housenger & US EPA, 2015). Fishel (2006) says that controlling pests encouraged a more efficient means of livestock production. Livestock consumes disease infested plants that cause sickness or even death. Pesticides have many positive benefits for the agriculture industry that can be traced directly to humans. These crops are also important because bees need flowering plants to pollinate. Our economy relies on the value of bees as pollinators and this is reflected in the billion-dollar annual vegetable production industry (EPA, 2017). Thus, the continuing debate over the use of pesticides as a form of crop protection and weighing the crucial factors that this discusses about the decline in bee population numbers.

Scientific evidence points to pesticides having adverse effects on bees, specifically a group called neonicotinoids. Neonicotinoid pesticides are applied to crops in a variety of methods. The most common being a coating applied to the seed. When seeds are planted, the pesticide is absorbed, incorporating itself into all parts of the crop tissue. Other methods include spraying the growing crops and mixing the pesticides in with the soil (Simon-Delso et al., 2015). Goulson (2013) found the issue with these methods was that only 1.6-20% of the active ingredients are absorbed, with the majority remaining in the soil. This poses the question of what happens to the remaining pesticides that reside in the soil?

Tisler et al. (2009) concluded that neonicotinoids seep into water “through several different routes including direct leaching into groundwater and subsequent discharge into surface water, decay of treated plant material in waterways and direct contact from dust of treated seed, or spray drift into water bodies”(Tisler et al., 2009, pg. 911). The dissipation half-life of neonicotinoids, the time it takes for half of the pesticide to break down in water and become inoperative, is varied. A test by Goulson (2013) contained results that this half-life time ranged from 200 days to an excess of 1000 days. This means that neonicotinoids that leach into water can spread widely from their original application site before becoming fully nulled. This is important for bees, because as animals they require water. Bees coming in direct contact with neonicotinoids through their drinking water is a major concern.  According to Health Canada, one variant of neonicotinoids, imidacloprid, which is most widely used in their country, is seeping into Canadian waterways at levels that are dangerous to insects, such as bees. Because of these controversial effects they are proposing to ban imidacloprid in the provinces of Ontario and Quebec. Health Canada tested surface water in these locations and discovered an amount of these pesticides that is toxic to bees(Johnson, 2016).

Neonicotinoids remaining in water is not simply the full scope of the issue. All plants that are exposed to this water will subsequently absorb the pesticides and incorporate it into all parts of their tissue. A study by Krupke et al. (2012) found that dandelions growing near fields planted with neonicotinoid treated corn contained between 1.1 to 9.4 ng/g (nanograms/gram) of the chemical, showing that nearby plants that bees forage from will also infect them with pesticides. The same study detected average neonicotinoid concentrations of 9.6 ng/g in wildflowers collected from fields adjacent to fields planted with neonicotinoid treated corn, cotton, and soybean. The daunting fact about these concentrations is that the exposure of neonicotinoid required to directly kill a honey bee ranged as low as 4.5 ng/bee (Cresswell et al., 2012). A bee collects an average of 15 mg (milligrams) of pollen per trip out of the hive. In just 30 trips to a wildflower containing 9.6 ng/g of neonicotinoid, a honey bee can accumulate enough pesticide to outright kill it (Gill et al., 2012). There is no question scientifically that neonicotinoids are present in both the pollen of treated crops and nearby plants. However, are the bees coming in contact with them? Goulson and Wood (2017) found neonicotinoid concentrations in pollen taken from bees returning to nests placed next to untreated flowering crops ranged from 0 – 0.24 ng/g while pollen from nests next to treated flowering crops ranged from 0.84 – 13.9 ng/g. This evidence shows that proximity to treated flowering crops does increase the exposure of bees to neonicotinoid pesticides.

If this accumulated exposure does not cause direct death, it leads to a variety of other issues. Elston et al. (2013) study the issue of reduced offspring production. In an experiment, several colonies ingested a sublethal dose of 1 ng/g of neonicotinoids. Dosed colonies had reduced nest-building activity and produced significantly fewer eggs and larvae, with one group producing no larvae at all over the 28-day experimental period. Colonies exposed to this 1 ng/g sub-lethal dose also experience reduced foraging, and therefore reduced growth on the individual level. Gill et al. (2012) exposed Buff-Tailed bumblebee (Bombus terrestris) colonies to two levels of neonicotinoids (0.7 and 1.4 ng/g plus control 0 ng/g). Compared to the control colonies, pesticide treated colonies had workers bringing back smaller volumes of pollen, foraging for longer durations, and overall having more unsuccessful foraging trips. Treated workers collected pollen less frequently, with 59% of foraging bouts collecting pollen versus 82% for control workers collecting pollen, a substantial decline of 28%. The conclusion of this experiment is that exposure to neonicotinoids at these concentrations significantly reduce the ability of bee workers to collect pollen. A reduced ability to collect pollen directly results in a subsequent impact on their reproductive output and individual growth.

Another threatening secondary effect of this sub-lethal exposure is a weakened immune system. An immune system is responsible for protecting a body against infections, disease and other potentially harming foreign substances (Live Science, 2016). Pettis et al. (2016) showed that bees exposed to either 0.5 ng/g or 2 ng/g of neonicotinoids both had the same substantial growth of parasites while bees exposed to 0 ng/g only had minute growth. As VanEngelsdorp et al. (2009) showed in their experiment, 55% of CCD colonies were infected with 3 or more viruses as compared to 28% of control colonies. Colonies co-infected with 4 or more viruses were 3.7 times more frequent in CCD colonies than in control colonies. Both studies conclude the simple fact that the weakened immune caused by neonicotinoids increases the risk of acquiring deleterious conditions, in both intensity and quantity.   

The indirect effects of reduced population growth, increased exposure to parasites and pathogens, reduced worker output, and memory troubles coupled with the direct effect of increased mortality, can be a dangerous combination for bees. Due to this intense threat on honey bee populations, the United States Department of Agriculture should implement and enforce a ban of neonicotinoid pesticides which both indirectly and directly cause CCD. Neonicotinoid pesticides measurably harm bees according to many studies. One study by Rundlöf et al. (2015) found that the use of neonicotinoid seed coating caused a significant reduction in wild bee population. Bees exposed to the seed coating were only found in a density of about 20 bees / 467 m². In the control group, bees were found at a density of about 40 bees / 467 m². The presence of the insecticide in this experiment caused bee population to be reduced by 50%.

Not only do pesticides play a role in the effect on bees survival, they also have a significant impact on our economy. Fishel (2006) stated that from the chemist’s laboratory bench to the market shelf, most pesticides will take an average of 5 to 9 years at a cost up to $250 million per pesticide. Banning a substance, such as neonicotinoids, would not only save time and money but it could lead to a much larger scale ban. In some parts of Europe, there was a partial ban on three types of neonicotinoids (clothianidin, imidacloprid and thiamethoxam) from 2013-2015. Europe is revising the idea and considering a total neonicotinoid ban, and France is planning on putting a full ban in place by 2018 (Loury, 2016). This is not predicting a ban of all pesticides as a whole, but those most impactful to bees. The US could implement the same type of ban if more data and examples of CCD due to pesticides are presented.


CCD is a detrimental condition bees are suffering from, unfortunately the cause of which is still being hypothesized due to numerous possible causes. Many of the scientists that conducted research on the topic admit themselves there needs to be further reasearch done to prove their theory on the cause of bee population decline (Rundlöf et al.,2015; Kuglin, 1980; Colla & Packer, 2008; Exley, Rotheray, & Goulson, 2015). CCD within a single bee population can be caused by various stressors being researched. Bee populations worldwide are suffering the effects of CCD; we need to eliminate the cause as quickly as possible. The signs point to pesticides, specifically neonicotinoids, as the major reason behind this disorder that is plaguing many hives. A ban of these chemicals has the potential to completely solve the issue, or at a minimum stall the decline and provide more time for research and understanding.



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  1. Really interesting article! Thanks for sharing! I really hope we can find a solution soon to the huge decrease in the bee population we’ve been seeing. With more people and more demand for food, less bees create huge problems when it comes to accessing certain foods. I don’t know what we would do if we weren’t able to produce certain foods because of this.

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