Perspective: Pollinators and People

Introduction

Humans depend on the cultivation of a wide variety of crops for their food, fuel, fibre, medicines, and cultural expression^[1]. Some crops are wind pollinated (grains, many nuts) but many require pollination by animals, including insects such as bees. A biological imperative of living organisms is to reproduce—to create offspring for the next generation. Without this, species would simply cease to exist. In plants, reproduction involves passing genetic material through pollen to ovules^[2] to set seeds, which may stimulate the production of fruit.

The diversity of plants is reflected in the diversity of animals that pollinate them including bees, wasps, flies, beetles, moths, butterflies, birds, bats, or other small mammals. Humans consume a large variety of seeds and fruit, some of which are produced and eaten globally (coffee, mango, avocado, tomato, cucumber, squash, apple, strawberry, pear, melons), and some of which are more regional (feijoa, durian, kiwano, cherimoya). Although the diversity of animals that acts as pollinators in natural systems is extensive, agricultural systems, where most human food is produced, are disproportionately dependent on a single group of insects: bees.

Bees pollinate plants by inadvertently transferring pollen between the sexual organs of plants (male stamens and female pistils) as they visit flowers to collect their food. Like humans, bees fuel their activities, maintain their physiological processes, mature sexually, and feed their offspring through nutrients consumed as food. For bees, the essential nutrients (carbohydrates, proteins, fats, vitamins, minerals) are consumed in the form of pollen, nectar, and oils. Both plants and animals have coevolved a complex system of rewards, deterrents, deceptive manipulation, and structural elements that make the system work to the advantage of all involved^[3].

Bees and People

Some bee species are more intimately connected to human behaviour than others. When people think of pollinators, they often think of the Western honey bee (Apis mellifera). Humans have a long history with the honey bee, with evidence of honey harvesting as far back as 15,000 years ago^[4]. The modern human reciprocal connection to honey bees is so strong that there are professional beekeepers who manage honey bees to produce honey and beeswax and to provide crop pollination services, in much the same way as people manage domesticated animals such as cows, sheep, pigs, chickens, and horses.

Some bees can be considered charismatic microfauna, or species that stimulate action and awareness in humans. For example, the giant panda (which is commonly referred to as charismatic megafauna), has become a well–recognized symbol for the World Wildlife Fund. For insects, bumble bees are often pictured as cute, fuzzy creatures that elicit similar positive responses from people. This intimate human-bee interconnection is deeply felt and forms the basis for the strong reaction to such slogans as “Save the Bees.”

When people think of bees, they may have a mental image of a fuzzy bumble bee. One study, however, found that for many Canadians, the honey bee is something of a stand-in for all bees^[5] and has become a symbol for conservation and environmentalism, despite the fact that honey bees in the Americas are more like domesticated animals than wild, native animals, and are not on any formal species-at-risk lists.

In tropical climates, although they produce far less honey, stingless bees are also managed by beekeepers for their pollination services^[6] and to produce honey valued for its medicinal properties.

Not all bees produce honey. Besides honey bees, bumble bees, and stingless bees, there are other solitary bee species that have longstanding reciprocal relationships with humans, often around the provision of specialized crop pollination services that surpass the efficiency of honey bees^[7]. These include: alfalfa leafcutter bees (Megachile rotundata) and alkali bees (Nomia melanderi), both important for alfalfa seed production^[8]; blue orchard bees (Osmia lignaria), important for orchard crop pollination^[9]; and squash bees (Eucera [Peponapis] species and Eucera [Xenoglossa] species), which are important pollinators of pumpkin and squash^[10].

In these cases, we have a three-way reciprocity with bees. Rather than interacting through a product like honey or beeswax, the primary exchange occurs via a human-grown crop that the bees pollinate. The crop provides forage and provisions—and sometimes sleeping and mating habitat—for the bees, and pollination results in a successful crop for people.

Commercial Beekeeping

Social honey bees are the most abundant bees on Earth, primarily due to the global breeding programs for extensive use in agriculture, and their large colony size: about 100,000 individuals per colony, as compared to 300 individuals per colony for bumble bees, and about 5 offspring per nest for solitary bees.

The pollination services of honey bees in their constructed, mobile hives have long been thought to be critical for conventional agriculture that relies on large swathes of monocultural crops. However, increasingly, even in commercial systems, the important role of wild bumble bees, solitary bees, and stingless bees is being recognized, in some cases as more important than honey bees^[11].

Commercial beekeepers use the honey bee’s easy mobility and large numbers to deliver commercial pollination services to food crops across the United States. For example, every year in February, about 1.7 million honey bee colonies^[12] are taken to California’s Central Valley to pollinate the more than 800,000 acres of almond trees (Figure 2). After almond pollination is complete, the movement of managed honey bees across the United States by commercial beekeepers then continues to cherry, plum, avocado, apple, alfalfa, sunflower, clover, clementines, tangerines, squash, cranberries, and blueberries, across Washington, Texas, Florida, the Dakotas, Wisconsin, Michigan, and Maine (Figure 3).

Globally, crop pollination has an estimated market value of up to US$577 billion annually, far more than the value of honey. However, the movement of so many bee colonies to crops causes physiological stress to bees. Bees require a varied diet from a wide range of plants, in much the same way as humans need a diversity of foods to maximize nutritional intake. When generalist bees^[13] are forced to visit a single crop species instead of visiting a wide range of plants for their food, they, too, may experience reduced nutrition^[14]. Furthermore, at pollination hubs such as the California almond crop where millions of colonies are concentrated, pests and diseases are easily spread from one colony to another, and there is increasing evidence of pathogen spillover from managed bees to wild bee species^[15].

The term colony collapse disorder (CCD) became part of the mainstream narrative during the first decade of the 21st century when entire managed honey bee colonies began to mysteriously disappear from their hives in the United States, baffling beekeepers and scientists alike. Colony collapse disorder has become a catch-all term for all mysterious, undiagnosed deaths of colonies and it is likely that it has many causes. While colony collapse is not currently a significant problem, high rates of seasonal honey bee colony losses, especially in winter, are still of great concern to commercial beekeepers and anyone who enjoys insect-pollinated food.

Many management practices, including best practices for agricultural pesticide use, often dictate that honey bee colonies should be moved before spraying pesticides or that pesticides should be applied in the evening or early morning when honey bees are not active. These honey bee–centric guidelines do not protect wild bees that nest in or above ground, on or around these sites, and which cannot be moved. Unlike honey bees, many wild bees are active in the early morning or evening and so risk exposure to pesticides if spraying occurs at those times. In addition, there is a growing literature on the negative impacts of pesticide residues at sub-lethal levels for both managed and wild bees.

Honey bees are also used as surrogates for all bee species in risk assessments of agricultural pesticides, despite the fact that they are highly unusual compared to other bees. This surrogacy approach^[16] in risk assessment and best management practices does not consider the unique needs, behaviours, or habitat of native, wild bees, who do not live in mobile hives that can be moved during pesticide application.

Bee Diversity

Bees are a vastly diverse group of living organisms, with an estimated 20,000 species that have been identified on Earth—nearly the same number as all the mammal and bird species combined^[17]. These diverse bee species also have diverse foraging needs and food preferences. Bees are intimately involved in pollinating roughly 75% of the most productive crops, accounting for 35% of global crop volume^[18]. This is where the notion of “one in three bites of food” is derived, which is commonly cited as the contribution of bees to human food crops. While all bees forage on plants to collect their food, bees vary greatly in biology, behaviour, food and habitat preferences, sometimes based on millenia of coevolution with the plants they feed from and hence, pollinate.

The differences in social behaviour, food preferences, and living conditions of these myriad species are many—some are social, others semi-social, most are solitary.

Most bees collect and eat nectar and pollen in unprocessed form. Others, such as honey bees, process nectar into honey and form bee bread from pollen, while still others collect and consume plant oils instead of nectar. Not all bees can fly the same distances from their nests to food sources. Honey bees can forage at distances up to 8 kilometers from their hives, whereas bumble bees are restricted to a radius of about a kilometer, and many solitary bees can only access nectar and pollen from plants within a range of 100 to 500 meters from their nests. This raises further questions about the effects of commercial honey bee migration and introduction of millions of managed honey bee colonies into agroecosystems at crop pollination hubs (such as the California almond crop). While evidence is still lacking in this area, the potential for managed honey bees to spread parasites, pathogens, and outcompete native, wild bee species in these contexts is clear.

In terms of nesting sites, some bees live in large cavities or constructed hives, others live in the hollow stems of plants or other small cavities, and some bees are nest parasites: instead of making their own nests, they insert their eggs into the nests of other bee species and have no role in provisioning those nest cells, much like the behaviour of cuckoo birds^[19]. Most, however (about 70%), build their nests in the ground.

Pollinators in Peril

Beyond concerns for the Western honey bee, there is evidence that other pollinators are in peril. In North America, of the native bee species with sufficient data to assess, more than half are in decline with nearly one in four at risk of extinction.^[20] The emphasis on only a couple of bee species, and the lack of understanding of the diversity of bees, has significant implications for conservation efforts and action campaigns. Unfortunately, due to a lack of research, the extent of threats and population declines in many species is not known.

In contrast to a positive reciprocal relationship, humans may also contribute to the decline of bee species. This takes place in several ways: by degrading and fragmenting landscapes so that there is less habitat for bees; by driving climate change that may create inhospitable conditions for bees or the plants that provide them with pollen or nectar; by inadvertently introducing invasive species, pests, or pathogens, often via managed bees such as honey bees or bumble bees; and by exposing bees to pesticides used to control pests in crops.^[21] Our own food system, which need bees, is also putting them in peril.

These anthropogenic pressures may lessen the strength of the reciprocity of the human-bee-crop relationship. Increasingly, humans have become aware of the connection between bees and food and the human role in bee declines. As such, initiatives to address these concerns (e.g., World Bee Day and Bee City) are growing in popularity, including increasing and enhancing education and creating pollinator habitat in a wide variety of eco-regions and contexts.

One example of such an initiative is Bee City (Figure 5). The Bee City movement began in the United States in 2012 in Asheville, NC. In 2016, it established itself in Toronto, ON, with a growing number of Bee Cities being created each year. As the American and Canadian programs expanded, they merged with the Xerces Society for Invertebrate Conservation (June 2018) and Pollinator Partnership Canada (December 2020), respectively.

To get Bee City certification, municipalities (and First Nations communities in Canada) commit to pollinator education and habitat creation. The ways that each Bee City chooses to do this is determined at the local level. Every Bee City has unique characteristics that help to inform decision-making processes and interventions, making Bee City a truly place-based initiative. For example, municipalities containing a significant amount of agricultural land may focus on different interventions than those with a lot of urban green space or those with primarily residential properties.

Conclusion

Human food systems currently depend on the mobility of one species of bee, the Western honey bee, to pollinate vast swaths of monocultural crops. This is a precarious dependency that has negative outcomes for both bees and humans. Honey bees are stressed by traveling long distances on trucks, and then become exposed to a melting pot of disease and parasites at each stop (as they mix with other transported colonies). Humans are also at risk, potentially losing all crop pollination services should this single species collapse under a devastating disease or disorder such as colony collapse disorder (CCD).

A better approach would be to recognize the value of the diverse pool of insect pollinators available to pollinate crops and then create systems that support those insect pollinators in the localized areas where they are needed. This includes protection from exposure to pesticides and maintaining flowering plants outside of the period when the crop needs to be pollinated. The very cropping systems that depend upon pollinators thus have the potential to support those pollinators or to harm them, depending on whether humans regard pollinator diversity in the context of reciprocity or resource exploitation. True reciprocity requires adjustment, but provides long–term sustainability to the plant systems that humans and bees alike depend on for food.

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