What is the role of bees in the food system and the preservation of global biodiversity?
Bees are the main pollinators of plants and crops in terrestrial ecosystems thus, they are essential providers of the ecosystem service of pollination -the transfer of pollen from stamens to pistils in the flower-, that is, from male to female organs in the plant, a process of great value for natural ecosystems and the agroindustry. Pollinators are, thus, central to global biodiversity due to their fundamental role in natural systems and agriculture: without pollination, ecosystems collapse, and many food sources would be lost, among other consequences.
Bees are pollinators par excellence and suffer high pressure: reduced flower diversity, continued exposition to pesticides and contact with parasites we humans accidentally spread with the bee trade. It seems this situation will worsen in the future and to all that, we must add climate stress and the disappearance of green spaces due to the insatiable demand for land for urban developments. Estimations indicate that the human population will reach 9 thousand million in 30 years, and together with the accompanying landscape conversion, the role of bees will be even more related to human survival.
Bees such as the European honey bee (Apis mellifera) and wild pollinators such as bumblebees (Bombus terrícola, Bombus dahlbomii i Bombus occidentalis) have been declining in the few last decades and some species are even considered extinct, as in the case of Bombus franklini, of which there are no observations since 2006. Despite the existence of studies indicating wild bees and bumblebees population decline, there is still a need for data as they comprise a diversity of taxa with complex responses. There is also a lack of data about pollinators in certain regions of the world since most available information comes from the Americas and Europe.
We need good answers to many questions so studies on bees have been encouraged in all five continents. In particular, we need descriptions of the population status of the various bees species (their abundance, above all, for there is a large gap in that knowledge) dynamics and the factors affecting their survival, such as pesticide use, changes in land use, urban development, habitat loss, parasites, invader species, interactions among factors, etc. to be able to intervene in their responses to climate change..
Climate change will impact bee biodiversity, as with most insects, and forecasting the precise effects is difficult since they will be the sum of many different factors. That said, many studies agree that habitat loss will be the strongest and most universal of those factors. followed by invading species and parasites, and pesticide use
The problem with the lack of studies is that we don’t have data on bee abundance and distribution, especially for wild bees. In addition, there are still undescribed species. Without this knowledge, it is difficult to estimate bee populations decline and to design prioritised conservation strategies.
THE PRICE OF CROPS AND POLLINATORS
Most crops grown in natural conditions depend on insects for pollination. More specifically, 73% of the world’s crops are pollinated by bees, while the remaining portion would involve flies, bats, wasps, beetles, birds and butterflies in this order.
In exchange for their help in plant reproduction, pollinators get food (nectar, pollen or both). This relation of mutualism (both parties involved benefit) has lasted and evolved for centuries by means of the coordinated anatomical and functional characteristics of its members; for example, the length of the proboscis in insects and the depth of the floral tube. Thanks to this mutualism many terrestrial ecosystems, natural and artificial, are possible.
The fraction of crops requiring animal pollination has increased approximately by 45% since the lands covered by crops depending on pollinators have increased. This fact takes us to a situation where demand outstrips supply.
Nature supports all human activities and life. The goods and services nature provides are vital for our current and future well-being and our economic and social development. Of all these goods and services, which we call ecosystem services pollination is indispensable, both for natural systems’ correct functioning and food production. In fact, this is also so in terms of monetary value: the total economic worth of the world’s crops has been estimated at 156 billion euros annually. This increase in dependence on pollination together with a climate change scenario marked by a reduction in bee biodiversity and its physiological effects and behaviours of lesser pollinating efficacy, has worried a number of sectors.
On the other hand, it is important to note that most crop pollination at a worldwide scale is done by wild pollinators and not by honey bees. This is why increasing the number of honey bees is unlikely to work as a solution for a pollination crisis in a situation of climate change. And even if it were part of the solution, relying on only one species would be a risky strategy.
EFFECTS OF CLIMATE CHANGE: BEES, PLANTS AND THEIR POSSIBLE MISMATCH
Honey bees (Apis sp.) are the main domestic pollinators used given their high foraging potential and are currently the pollinators of the most economically valued crops globally. They are widely distributed, comprising a diversity of climates: thus, they have a high genetic biodiversity and, as a consequence, a high adaptation potential. Moreover, honey bees are among the few bee species whose adults remain active in winter and regulate the temperature of the hive. This is why many of the studies assessing the decline in pollinator populations and the associated economic losses focus on this species. Below, we list the potential effects of climatic change on bee populations:
- Climate change happens too fast, and, despite their adaptability, bees wouldn’t have time to adapt so, they would migrate to higher latitudes and altitudes in search of more adequate climate conditions. Plants, on the other hand, would have the same problem and would answer similarly. Then, two scenarios are possible:
- If plants and pollinators simultaneously migrate together, pollination could keep happening, but this coupling between flower and pollinator could be compromised and could finally be lost since pollination depends on the phenology (the relation between periodic changes in climate factors and stages in the life cycle of organisms, such as reproduction) of crops and insects and climate change.
- On the other hand, climate change could affect the quality of the floral environment and, in addition, increase or reduce the development ability of bee colonies, impacting their life cycle and, thus, causing a reduction in pollination.
- These timing (phenological) mismatches between plants and bees could have serious consequences: they could affect plants too because they would not receive as many visits by insects and would spread less pollen, while bees would face a reduction in food availability and the consequent increase in vulnerability to pathogens. If, in addition to climate and nutritional stresses, plants are exposed to pesticides, the vulnerability would only increase since the effects of pathogens on bees would be stronger to the point of affecting their biological fitness (essentially, survival and reproduction).
- Climate change will bring atmospheric instability and with it floods, droughts and a higher global temperature. Will plants be able to survive the fast arrival of these climate conditions? If the answer is positive, will their pollen and nectar be good for bees? One example of this is that, when it rains, honey bees avoid acacia flowers because their nectar becomes too diluted. On the other hand, during droughts, pollen production and nutritional quality go down.. This is important because larvae are the ones in need of a pollen diet.
- Extreme heat is also an obstacle to storing food. As a consequence, bees don’t have food enough for the winter and they will not be able to adequately feed the larvae. The effect is that there will be fewer workers the following spring and the members of the colony will have a weakened immune system.
PESTICIDES, ONE MORE PRESSURE
Bees have been exposed to pesticides due to the intensification of farming, to the point of altering their biological fitness. The situation is likely to worsen since routine exposure to pesticides is unlikely to decrease, causing sublethal and even lethal effects on bees.
At the individual level, continued exposition to toxic substances can affect both the detoxification mechanisms and the immune responses, causing bees to be more vulnerable to parasites. The usual pesticides, such as imidacloprid, fipronil or thiacloprid, negatively affect the learning processes and orientation ability of adult bees and cause an ailment in bees they may convey to the larvae. These products are among the main ones responsible for the bee population decline. They belong to the neonicotinoid group, neurotoxins that affect the nervous system of insects.
Pesticides also have unfavourable effects at the colony level, since some outbreaks of diseases have been associated with them. This would indicate that more intense infections may affect bees’ tolerance to pesticides. Thus, pathogen-pesticide interactions can contribute to increased mortality in bees and other pollinator populations.
HABITAT LOSS AND URBAN BEES
The effects of habitat loss will show in the long run. It is one of the more important factors responsible for bees’ decline since flowers, places for hives and other resources are found precisely in the habitat.
As urbanisation increases, the loss, fragmentation and destruction of natural habitats accelerate, and the need emerges to intensify the studies on the bee populations living in cities, still a relatively unknown environment. In fact, if a sustainable city model and adequate conservation measures were to be applied, urban surroundings might become an opportunity to relax the loss of pollinators.
We must attain city designs with enough adequate habitats for natural populations of bees; it must happen sooner or later, so the sooner the better.
BEE PROTECTION AND SUSTAINABLE POLLINATION
With all we have expounded here, it should be evident that we need to take measures for stopping bees’ decline. A diversity of factors affects bees and it can be complicated to draw clear conclusions, but this does not mean that we don’t need conservation measures. Such strategies must consider the type of land and the socio-economic development of the area. Below we list some generalist measures that would help bees:
- Enhance biodiversity of floral resources: provide pots and gardens with suitable floral species, plant flowers in field margins, or leave patches of natural habitat between or near farmland. This promotes crop pollination and bee biodiversity.
- Education and popularisation: explain the problem implied by losing bee populations and help citizens to get closer to nature since we live more and more in urban surroundings.
- Spatial planning: sustainable cities. A city with enough green areas, urban vegetable gardens or vertical gardens would be compatible with social and economic activities as well as with the environment. At the end of the day, green areas are necessary to produce oxygen and thermoregulate city air.
- Pesticide reduction: especially of those used without due measure and, often, without motive. It would be highly desirable to develop short- and long-term risk assessment programmes, a habitat and pesticide-specific application protocol, and an effective advisory and incentives system for the farming community.
- Provide suitable nesting sites, whether structures, cavities, bare ground or simply by increasing native floral diversity. This should also be considered in city planning.
- More studies and monitoring programmes: there is a general lack of knowledge on some fundamental issues. It is important to develop more efficient monitoring methodologies and methods to estimate the diversity, abundance and distribution of bee species. Finally, it would be useful to develop indices or a warning system to indicate how far we are from this pollination crisis in order to take appropriate measures as soon as possible.
- Prevention of introductions of non-native bees and pathogens: control trade in bee species and implement strict quarantine controls for every movement made. The introduction of non-native bee species must be prevented at all costs, and for this reason, policies must also be tightened.
- Learn more about bees and climate change in this talk by Ignasi Bartomeu: What is wrong with bees?
