In recent years, the idea of a world without bees has transcended numerous social and political spheres. The scientific community has been warning about the disappearance of bees during years without any consequence. But now, it has become an issue of major concern, acquiring a media relevance like never before. At the end of 2017, the EU decided to take matters into its own hands to prevent this tragic ending for bees.
Why would it be a problem that bees disappear from Earth? And which measures has the UE take in order to address this problem?
The DDT and Rachel Carson
The use of pesticides has been a common agricultural practice from the very beginning of agriculture. At the beginning, the use of organic chemicals derived from naturals sources, as well as inorganic substances such as sulphur, mercury and arsenical compounds, was very common. However, they eventually stopped being used due to their toxicity (especially, phytotoxicity). The growth in synthetic pesticides accelerated in the mid-twentieth century, especially with the discovery of the effects of DDT, which became one of the most widely used pesticides of all time. DDT became famous due to its generalist insecticidal effects and low toxicity to mammals and plants, being used to eradicate household pests, fumigate gardens and control agricultural pests.
DDT resulted to be very effective against insect vectors of deadly diseases such as malaria, yellow fever and typhus, thus becoming even more popular.
However, the overuse of this and other pesticides eventually began to cause severe human and environmental health problems, because some of these products started to contaminate soils, plants and their seeds, and to bioaccumulate within the trophic nets, finally affecting mammals, birds and fishes, among others. The indiscriminate use of pesticides and their effects were denounced by Rachel Carson through her most famous publication, “Silent Spring”, which was distributed in 1962.
From Carson to the neonicotinoids
Since Carson denounced the abusive use of pesticides, the world has witnessed the birth of many new substances to fight crop pests. Since then, researches have focused on finding less toxic and more selective products in order to minimize their impact on both human and environmental health. Could we say it has been a success?
Yes… and no. Although their use stopped being so indiscriminate and famers started betting on the use of more selective products, there were still some open fronts. Fronts that would remain open until today.
Between 1980 and 1990, Shell and Bayer companies started working on the synthesis of a new assortment of pesticides to face the resistances that some insects have acquired to some of the most widely used substances those days: the neonicotinoids. Neonicotinoids are a class of neuro-active insecticides chemically similar to nicotine; they effect the insect nervous system with a high specificity, while having a very low toxicity to mammals and birds compared to their most famous predecessors (organochlorides, such as the DDT, and carbamates). The most widely used neonicotinoid nowadays (and also one of the most widely used pesticides worldwide) is the imidacloprid.
However, far from getting famous for their effectiveness, the use of neonicotinoids began to get controversial for their supposed relationship with the disappearance of bees.
How do these pesticides affect bees?
For some years now (2006 onwards) the neonicotinoids are in scientists’ spotlight as one of the main suspects of the disappearance of bees. However, it has not been until now that something that scientists had been denouncing for years has finally been assumed: that neonicotinoids cause a greater impact than it was thought.
Unlike other pesticides that remain on plant surfaces, some studies state that neonicotinoids are taken up throughout their tissues, thus being accumulated in their roots, leaves, flowers, pollen and nectar. Also, that nearby fields are polluted with the dust created when treated seeds are planted and that plants derived from these seeds will accumulate a major amount of pesticide than sprayed plants (as it is explained in this publication of Nature). This causes bees (as well as other pollinating insects) to be exposed to high levels of pesticides, both in the crops themselves and in the surrounding foraging areas. These same studies have revealed with less support that these products may persist and accumulate in soils, which may affect future generations of crops.
Some of the negative effects on bees that have been related to neonicotinoids are:
- Altered immune system, reduced overwintering success and reproduction in both honeybees and wild bees (according to this recent study published in Science).
- Risk of disorientation in bees when looking for food (foraging habits) in both honeybees and wild bees, as well as communication disruption in colonial bees.
- Enhanced negative effects by the interaction with other pesticides.
- Contribution to the CCD (Colony Collapse Disorder). This phenomenon is characterized by the massive disappearance of worker bees from a colony, which leave behind the queen along with food, its larvae and some bees that take care of them. This phenomenon has been recorded numerous times throughout history; the last one occurred in the USA in 2006, when a large number of honey bee colonies (Apis mellifera) began to collapse (until 2013, about 10 million hives have disappeared, almost 2 times more than what is considered normal). The CCD is a multifactorial phenomenon, in which the action of pesticides seems to be only one of a long list of possible triggers.
In addition to the effects of neonicotinoids, other important causes must be taken into account: climate change, less food sources and changes in soil uses.
What would happen if bees disappear?
Colonial bees (like honeybees) are the most famous among bees. However, they only represent a mere portion within the great diversity of known bees, most of which have solitary life habits and build their nests inside small cavities. The ecological importance of solitary bees is equal to or greater than that of honey bees, but effects that neonicotinoids have on them are still poorly studied. Together, bees are among the most efficient pollinating organisms.
According to this study carried out in German territory and published in POLS One at the end of 2017, a large part of flying insect diversity (including numerous pollinators) and up to 75% of their biomass have decreased in the last three decades due to the interaction of several factors. And if that was not enough, the authors say that these numbers can probably be extrapolated to other parts of the world.
What would happen if both colonial and solitary bees disappear?
- Disappearance of crops. The production of many crops, such as fruit trees, nuts, spices and some oils, depends entirely on pollinators, especially on bees.
- Decrease in the diversity and biomass of wild plants. Up to 80% of wild plants depend on insect pollination to reproduce, as it happens with many aromatic plants. A decrease in the vegetal surface would lead to serious problems of erosion and desertification.
- Less recycling of soil nutrients. With the disappearance of the plants, the washing and deposition of soil nutrients would go down.
- Less biological pest control. Some solitary bees are parasitoids of other solitary bees and other groups of insects (natural enemies); their absence could trigger the recurrence of certain pests.
- Negative effects on higher trophic levels. The disappearance of bees could cause a decrease in the diversity and biomass of some birds that feed on pollinators.
- Disappearance of bee-derived products, such as honey or wax.
The UE bans the use of neonicotinoids
Facing this reality, several governments have tried to limit the use of pesticides as a part of the measures to stop the decline of bee populations and the resulting economic losses. To give some examples, since 2006 the biomass of honey bees has decreased by 40% in the US, 25% in Europe since 1985 and 45% in the United Kingdom since 2010, according to data published by Greenpeace.
To date, the more restrictive measures limited the use of neonicotinoids in certain situations or seasons. But at the beginning of 2018, the EU, after preparing a detailed report based on more than 1,500 scientific studies carried out by the EFSA (European Food Safety Authority), decided to definitively ban the use of the three most used neonicotinoids in a maximum period of 6 months in all its member states after demonstrating that they are harmful for bees: imidacloprid, clothianidin and thiamethoxam.
Will the objectives of this report be accomplished? We will have to wait …
. . .
Although slowly, the fight against the abusive use of pesticides is paying off. However, we will have to see if the gap left by some products is filled with other substances or if governments commit to adopt more environment friendly agricultural models.
Main picture obtained from [link].
All you need is Biology 