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The bees (Apis melifera) are a species of insects widespread throughout the world and with great economic importance. Thanks to bees we can obtain products such as honey, pollen, royal jelly, propolis and wax, in this article you can see the importance of bees. In addition, they have a very important role in agricultural and floristic production thanks to pollination. At the same time, numerous threats loom over them, including the destruction of their habitat, climate change, mites and parasites, diseases and pesticides. There are currently a large number of pesticides on the market and many of them are not well known about the consequences they can have on the environment. However, neonicotinoids, a type of insecticide, have caused great controversy due to the population declines of bees, bumblebees and solitary bees that they have caused in recent years. For this reason in Green Ecologist we are going to talk about what are neonicotinoids and their effect on bees.
What are neonicotinoids
The neonicotinoids They're a relatively modern family of insecticides widely used to treat and prevent insect pests in crops. They are applied against a wide range of chewing, boring and sucking insects such as coleopterans (beetles), lepidopterans (butterflies, moths and their larvae) and heteropterans (bed bugs).
These insecticides were developed and introduced to the market in the 90s of the last century as a safer alternative for the environment and human health. Previous insecticides such as DDT (dichlorodiphenyltrichloroethanes), organochlorines and organophosphates were banned due to increased resistance of insects, high toxicity in vertebrates (fish kills) and other organisms, and because of the potential bioaccumulation in fatty tissues and the poisoning of farmers and farmers.
Neonicotinoid insecticides derived from the natural toxin nicotine and they are classified according to their molecular structure. The different neonicotinoids that are known by their trade names are:
- Imidacloprid (first commercialized neonicotinoid).
- Thiamethoxam.
- Clothianidin.
- Dinotefuran.
- Nitenpyram.
- Acetamiprid.
- Thiacloprid.
Characteristics of neonicotinoids
Next we will talk about the characteristics of neonicotinoids:
- They are systemic: This means that the plant incorporates them into the sap and as it develops, it distributes them throughout the body (stems, leaves, pollen, flowers). They are applied by spraying on the leaves, in the form of granules that are buried in the ground or coating the seeds of the plants.
- High solubility in water: Thanks to this chemical property, the plant can incorporate them into its body at the same time it takes in the water.
- Low ground holding capacity: As they are not retained in the ground, their mobility through the environment is favored. This, together with the ability to dissolve in water, allows its displacement to aquatic ecosystems through surface and groundwater.
- Persistent in the environment: They present a high persistence in soils as they can be accumulated for years. In aquatic systems the persistence is moderate, and can last from several minutes to weeks. The persistence of neonicotinoids in both media depends on the light, pH, temperature, their chemical composition and the microbial activity of the place.
- They are neurotoxic: They block the transmission of the nervous impulse causing the death of the animal.
Effects of neonicotinoids on bees
Although neonicotinoids were designed as specific insecticides to kill the insect pests in agricultural systems, several studies have proven that they can affect other organisms for which they were not designed. The neonicotinoid controversy began in France in 1994, after the introduction of imidacloprid in agriculture, when some beekeepers noticed that bee populations in their hives were declining.
The effects of neonicotinoids in bees include an alteration in smell, memory and locomotion and the inhibition of feeding. The effects of neonicotinoids take a while to appear, and what's more, at first it is observed that hives increase honey production. This is due to the lack of food and the death of the workers. As the workers do not feed on it, the honey accumulates in the hives where it serves as food for the rest of the bees and the queen. To compensate for the losses of the workers, the hive produces new individuals until it reaches a point, the queen dies from excess neonicotinoids in your body as a result of chronic long-term exposure. Afterwards, the production rate of queens decreases by 85%, which hinders the future of the populations. Additionally, exposure to neonicotinoids weakens the immune system and makes them more susceptible to parasites and disease.
Thanks to the demands of environmental groups and scientific studies done over the years, at the beginning of 2022 the European Union has banned the use of three neonicotinoids (imidacloprid, clothianidin and thiamethoxam) in all outdoor fruit crops, although it does allow its use in the greenhouse. This could be good news for bees and other threatened land pollinators such as butterflies, moths, bees and hoverflies. Their disappearance in ecosystems is endangering ecological functions such as pollination in agricultural systems. However, there are other organisms threatened by neonicotinoids and of which not much is known, the aquatic macroinvertebrates.
In the following article we explain the causes of why bees are in danger of extinction.
Effects of neonicotinoids on aquatic ecosystems
Given the high solubility in water and the low capacity to be retained in the soil, concentrations of various neonicotinoids have been found in lakes, rivers, wetlands, groundwater and even in the sea. The presence of neonicotinoids in water puts aquatic communities at risk since organisms such as macroinvertebrates can be very sensitive to these chemicals.
The Aquatic macroinvertebrates are key bioindicators to study water quality, and also represent a significant component of biodiversity in most freshwater ecosystems. They act as predators of other organisms and plants or as a source of food for their predators such as other invertebrates, fish, birds and mammals. Some of the most sensitive macroinvertebrates are insects (ephemeroptera, woodpecker) and some crustaceans. The decline of macroinvertebrates due to neonicotinoid contamination can modify food chains. For example, in the Netherlands population declines were detected in some birds associated with the disappearance of aquatic macroinvertebrates due to the use of imidacloprid in agriculture.
According to the European Water Framework Directive (2000)[1] all member states must ensure the good quality of their ecosystems aquatic. There are maximum permitted thresholds for these compounds in water bodies, but in many cases they are based on the limited scientific knowledge that exists.
Recently, a Spanish study[2] has tested the effects of imidacloprid and a mixture of five neonicotinoids (imidacloprid, acetamiprid, clothianidin, thiamethoxam and thiacloprid) in Mediterranean aquatic macroinvertebrate communities. These neonicotinoids have been proposed to be included in the Observation List of substances that must be studied in water and which is included in the Water Framework Directive.
The results obtained show that the species most affected have been the larvae of various insects, an ephemericopter (Cloeon dipterum) and a subfamily of mosquitoes (Chironomini), and an order of copepods (Cyclopoida), small crustaceans that are part of zooplankton. These organisms have shown greater sensitivity to neonicotinoids than in other studies conducted in areas of northern Europe and other tropical areas. In this way, it can be seen how the presence of these toxins supposes an additional stress for organisms apart from the already harsh climatic conditions typical of the Mediterranean region that they have to face (high temperatures and lack of rain).
Furthermore, this study proposes maximum thresholds for these insecticides in the water so that they do not pose a danger to the organisms found in our aquatic ecosystems. These thresholds would be 0.1 micrograms per liter (one microgram equals 0.001 mg) and lower, depending on the duration of exposure, a much lower range than currently allowed by the European Union and which stands at 0.2 micrograms. per liter. Finally they demonstrated that the additive effect of neonicotinoids works in the short term, this means that the effects that each neonicotinoid individually has on organisms add up when they appear together in bodies of water. On the other hand, this additive effect has only been observed in short periods of time since it depends on the time it takes for each insecticide to degrade in the environment.
Finally, it should be noted that there is still much to know about the effects of neonicotinoids both in terrestrial and aquatic organisms, how environmental factors influence the effect they can have, nor what can happen when they are mixed with other insecticides, herbicides, fungicides or other chemical products that may be found in the environment. Therefore, it is necessary to investigate and stop the uncontrolled use of these chemicals.
If you want to read more articles similar to What are neonicotinoids and their effect on bees, we recommend that you enter our Ecosystems category.
References- https://eur-lex.europa.eu/legal-content/ES/TXT/?uri=LEGISSUM%3Al28002b
- Rico, A., Arenas-Sánchez, A., Pasqualini J., García-Astillero, A., Cherta, L., Nozal, L., Vighi, M. 2022. Effects of imidacloprid and a neonicotinoid mixture on aquatic invertebrate communities under Mediterranean conditions. Aquatic Toxicology. 204. 130-143.
