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It’s no secret: the bees are in trouble.

Biologists, beekeepers, gardeners and the general eating public have been sounding the alarm for over a decade now about the (Apis mellifera L.), and the in the Americas and Europe — as high as 50% of species in some regions. Yet research has illuminated that rather than any one predominant threat to bees, they are being accosted by .

Bees are complex creatures with that allow for their social structure, foraging behavior and ability to find and communicate quality food sources. While the European honeybee is widely kept in managed beekeeping hives and used to assist commercial agriculture, there are nearly of bees globally that act as crucial pollinators of the world’s plants. Pollinators, and especially bees, fertilize a staggering worldwide, including the majority of fruit and vegetable crop species. They help ensure global food security and improve the nutritional quality of our food supply, which is even more critical as we contemplate feeding a human population projected to by 2050. In short, we need them.

But despite the mass interest and earnest research into the plight of the bees, American managed hives still saw their on record between April 2019 and April 2020: 43.7%. Wild bees have also suffered significant and .

So how did we get here?

Loss of Habitat from Aggressive Agriculture

Bees have been in decline in the United States since the 1940s. The birth of chemical fertilizers following World War II and the newly dawned age of industrial agriculture eventually transitioned many local botanically diverse family farms into large industrial monocultures. Rather than and pollinator-friendly to help recover soils, industrial farms depend on chemical fertilizers and the use of pesticides and herbicides to maximize yields. These shifts have had precipitous impacts on bees, whose once-symbiotic relationship to human farming is now under threat.

Professor Marla Spivak made the astute comparison in her between large-scale monoculture and a pollination food desert. Enormous swaths of land used to plant single crops not only destroys native bee habitat, but sequesters acres of land where bees are unable to locate meaningful nutrition, save for the brief flowering season of a single plant species. The result is "” for bees. This is non-trivial, as nutrient deprivation can to disease. It is especially damaging for native bee species, which may be to local flowering plants. and can help reduce these effects and boost bee health.

Ubiquitous Use of Pesticides, Herbicides and Other Chemicals

In focusing on lethality from acute exposure to a single chemical, many regulatory studies overlook the realistic exposure of multiple, chemicals on a variety of bee outcomes, such as feeding or foraging behavior, immunity and protection from parasitic or viral disease. Pollen carried back to bee hives and honey or wax derived from it have been found laced with , , and even unclassified chemicals that may be degradation products of active ingredients.

in particular are a class of insecticide that act on the neural synapse of many insects, such as beetles or leaf hoppers. Their use in the United States between 2003-2011. Bees are not a target organism. While do not demonstrate an overtly negative effect on bees, others argue that they , , , and The specific effect of neonicotinoids to weaken the may also have broad impacts for overall hive survival.

Glyphosate, the most widely used herbicide in the world, may also be impacting bees via . Bees have 5 core gut bacteria and several other groups that are often, but not always, present. One of the primary gut microbes, Snodgrassella alvi, is particularly important in , and also happens to be one of the species in a . The oxygen gradient within the gut is , meaning the loss of S. alvi, an oxygen consumer, may . Indeed, glyphosate exposure was also associated with a loss of , which are a core microbiome components that and even found in the bee diet. Thus the impact of glyphosate on the bee microbiome may render bees more vulnerable to and Glyphosate has also been implicated in during the larval stage, including at the .

Parasites

Possibly one of the most destructive blights to western honeybees has been parasitism and viral disease, in many cases from non-native species and emergent pathogens. Topping the list is the (Varroa spp.), an ectoparasite which clings to its host and or metabolic center. Varroa mites are a native parasite to the Asian honeybee, Apis cerana, which has evolved a to minimize their damage. They began moving westward with bee colony trade in the late 1940s, and . Western honeybees do not display the same protective mechanisms as Asian honeybees, making Varroa a formidable and potentially lethal foe for a hive. If that weren’t enough, mites are also ready vectors for viruses, such as or , which renders bees unable to fly.

Bees are afflicted by numerous other blights from across the phylogenetic tree of life. The hive beetle is another foe to western honeybees, within the last several decades, that damages the hive and . Microsporidians of the genus (1 species of which was to western honeybees) are gut parasites that and in the bee. also parasitize bees, the foremost of which is , which predominantly attacks larval tissues and impairs healthy hive growth.

The most of the so-called “murder hornets” (Asian giant hornet, Vespa mandarinia) to the United States and Canada in late 2019 is yet another alarming development for western honeybees. The Asian honeybee, which co-evolved with V. mandarinia, has developed a defense mechanism in which a scout hornet entering a hive is smothered by an ambush of hundreds of bees, who beat their wings and raise the . This ‘bee ball’ heats and suffocates the hornet to death, staving off future attack. European honeybees, by contrast, against the hornet, leaving them vulnerable to the . V. mandarinia has so far only been sighted in regions of Canada and northern Washington state, and active efforts are in the Americas.

Climate Change

Climate change is famously responsible for the and its . However, for bees in particular, rising carbon dioxide levels of one of their primary food sources: pollen. Bees derive their entire foraging diet from nectar (carbohydrates) and pollen (protein), and may have limited sources of pollen during late season gathering. Nutritional deficits in pollen specifically reduce the bee’s ability to , and can have on the growth of a colony.

Beekeeping Practices

In nature, species adapt to selective pressures that generally favor those most able to overcome the stressors at hand. This applies to parasites too, which must strike the right balance between host immunity and disease spread to be successful. Highly virulent pathogens run the risk of killing off their host reservoir and being unable to spread, thus the selective pressure for many pathogens is to reduce virulence over time or elect tradeoffs with the host.

However, can artificially remove the stressors that promote such evolutionary calibration and instead provide an environment that inadvertently selects for greater disease spread and more virulent pests. This happens in the following ways:

• Increased Population Density: While wild beehives house approximately 18,000 bees, commercial bee colonies can range from . This increased density makes bees . Moreover, larger commercial apiaries are likely to cluster colonies together, which is associated with . Clustered hives have (bees that enter a different hive), which increases pathogen spread.
• Artificial Repopulation: When a hive is devastated by a disease, the pathogen’s ability to spread is limited because there are no new hosts to infect. However, in managed hives, an entirely new colony of susceptible individuals is brought in to replace the dying hive. This for a pathogen to reduce virulence, and instead rewards the most deadly pathogens. However, can help strengthen the bees.
• Incomplete Pest Removal: Treatments that only partially reduce pathogen volume without destroying them, such as routine application of ., select for resistance and more hardy pathogens.
• Agricultural Travel: Many managed honeybees follow a national circuit according to agricultural pollination needs. It’s estimated that of all managed honeybee colonies in the United States migrate to California to help pollinate during almond season. What this means practically is that bees from all over the nation are congregated in one setting, which presents the risk of disease spread across multiple geographical locations when the bees return home. There have also been reports of from such travel.

Colony Collapse and the Synergistic Effects of Multiple Stressors

Although each of these stressors are formidable on their own, the real threat is in their synergy.

For example, pesticides and herbicides are thought to be . However, the demonstrated contributes to exposed bees' susceptibility to pathogens. Meanwhile, bees are facing a higher pathogenic risk due to a combination of for which they don’t have an evolved defense, and that put them at greater risk of disease spread. The added effect of chemicals, such as  reduces their natural defenses even more, along with their nutritional status. Moreover, from neonicotinoids interfere with the foraging behavior of bees, making it difficult to bolster immunity with good nutrition. On top of that, to plant chemistry reduce the nutritional benefit of each foraging venture. The compounding malnourishment of the bees in an unvirtuous cycle.

A particular form of hive failure known as occurs when the majority of adult bees in the hive disappear, leaving only a queen, some nurse bees with larvae and plenty of food stores. Dead bee bodies are nowhere to be found. No single factor has been shown to definitively cause CCD, and it likely arises from a constellation of stressors. However, pathogenic assault on a hive is often a factor and several bee pathogens are associated with it.

It’s not just the honeybees. Wild bees are and environmental stressors that managed colonies are, with the added impact of . Where foraging habitats are shared between managed and native bees, diseases fostered in a managed environment can also and impact their survival as well.

How You Can Help the Bees

Despite the many stresses facing bees, each of us can do something to help. The following are simple ways to boost bees in your area:

• Plant Bee-Friendly Flowers: This is possibly the simplest and most . Whether it’s a single little pot of flowers outside your door or a large vegetable garden, flowering plants provide vital sources of the 2 main bee foods: nectar and pollen.
• Buy Organic: We tend to think of organic produce in terms of human health, but perhaps we should also think of the ecosystem that it supports. Organic crops can provide non-contaminated foraging space for bees on a large scale. Studies find that near retain an abundance of native bees in the area, whereas all other farms experience a much-reduced abundance and diversity of native bee species. As your budget allows, buying organic produce is a simple way to support bee-friendly agriculture.
• Build a “” to Shelter Local Bees: Many native bee species are non-aggressive and solitary. Providing them with (think birdhouse) is a fun and educational way to help local pollinators thrive, especially in conjunction with a garden or nearby park.
• Reconsider Pesticides on Landscaped Plants: Agriculture is not the only source of chemical exposure for bees. Landscaped and gardened plants are still a source of pesticide and herbicide exposure for local foraging bees. If you have a yard with plants or flowering trees, consider growing them without the use of chemicals.

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