Pollination is of paramount importance for the world agricultural production. The service provided by pollinators is figured up to 153 billion $ equivalent to 9.5% of the value of total world food production. Bees are the major players in this activity, whether domestic or wild bees. For information, in 2009 the value of pollination of honeybees represented 11.68 billion dollars in the United States while that of wild pollinators amounted to $ 3.44 billion.
This fundamental ecosystem service is nevertheless threatened for many years because of multiple pressures on pollinator populations (pesticides, diseases, parasites, monoculture, invasive species, etc.). This trend has recently accelerated, with losses of exceptional herd numbers by beekeepers since 2006 (from 30% to 90% in the United States in 2006). This phenomenon is called Colony Collapse Disorder (CCD). It is characterized by the abandonment of the hive by bees and is differentiated by the effects observed due to traditional pesticides (dead bees «carpet»). The causes of this scourge are still unclear, but the impact of neonicotinoid insecticides combined to the action of new pests and diseases of bees, is one of the most plausible hypotheses.
Appeared in 1990, neonicotinoids are innovative by their systemic action. Used mostly as a seed coating, they have the ability to translocate through the plant to protect it from pests during its early stages. Popular because of its ease of use and flexibility (they can also be sprayed as a foliar application or irrigation), they are the most sold in the world with a market share of 2.6 billion dollars.
However, many scientific studies have highlighted the dangers of these substances to pollinators. Besides their immediate toxicity, which led to the successive ban of many products placed on the market (Gaucho, Regent), a study of the INRA recently proved their sublethal effects, which could explain the CCD. This led to the creation of a European moratorium in 2013 which is partially banning for two years the three molecules considered as the most dangerous (Chlothianidine, Imidacloprid and Thiamethoxam).
Neonicotinoids: a threat for bees
Despite the fact that pollinators are not the targets of neonicotinoids, they may be exposed and are particularly sensitive.
Routes of exposure to neonicotinoids for pollinators are manyfold. They may be faced orally ingesting pollen, nectar and honey after fabrication. This contamination can be done through flowers of treated crops or those from surrounding land due to the diffusion of neonicotinoids in the soil. They are achieved by direct contact when neonicotinoids are sprayed or due to releases of dust while sowing coated seeds.
It is possible that bees are also affected due to the contamination of their environment (soil, water, plant compounds). Wild bees are particularly sensitive to it because they usually nest in the ground and build their nests from plant materials.
The toxic effects of neonicotinoids are not confined only to the immediate death of pollinators:
Lethal doses causing death of bees are rarely reached orally (via pollen and nectar) on crops treated by seed coating but can be on crops treated by spraying or irrigation. Direct contact with dust coating during planting is deadly. The pollinator can succumb after exposure or chronic ingestion of sublethal doses. More problematic still are sublethal effects characterized by a multitude of symptoms. Motor and behavioral capacities of bees are disturbed causing their decline over time. Synergies were observed between neonicotinoids and other pesticides or pathogens. Few studies have been conducted on wild bees. Nevertheless, there are clear indication that they are also affected and even more because of their small size.
Recent studies (Vidau, 2011; Henry, 2012; Lu, 2014) link the symptoms observed in the case of CCD to sublethal effects that neonicotinoids have on bees. The widespread use of neonicotinoids in agriculture, coupled with the increased losses of pollinators, scientific studies supporting its harmfulness prove that they are not without risk and that drastic measures must be implemented.
Moreover, the persistence and accumulation of neonicotinoids in the soil, yet little studied, may increase the danger of contamination for pollinators.
Crops untreated by neonicotinoids can be contaminated with residues in the soil due to previous crops. Indeed, the service life of these molecules in the soil can reach several years. Neonicotinoids content in soil increases through accumulation when the cultures are treated consistently over time. Pollinators can then be exposed to much higher doses than those planned.
Limitations of the moratorium
Faced with the obvious danger of neonicotinoids for pollinators and thus for agricultural production in the long term, we conclude that these insecticides are clearly not sustainable. The EFSA has realized the importance of this issue by ordering the moratorium in 2013, however, the limitations of this decision are obvious: The ban of only two years do not allow to measure possible improvements without the use of neonicotinoids because of their characteristics (accumulation in soil, retention).
The ban of three molecules is insufficient. The neutrality of the other neonicotinoids still allowed was not proven. It is always possible to use these three neonicotinoids in periods when the bees are less likely to be exposed (winter crops, fruits and vegetables after flowering, etc.). However, the risks associated with contamination of the surrounding land through propagation and persistence of these molecules are not taken into account. Wild pollinators are not sufficiently considered in this Directive. Treatment of crops that do not attract honeybees remains authorized while they are likely to be pollinated by wild bees (potato, tomato, etc.).
Further more the partial authorization of the use of neonicotinoids affects wild bees because they nest in contaminated soils. Further studies on wild bees seem necessary for their importance in the pollination of wild and cultivated plants.
Available scientific studies already allow to measure the extent of risks arising from neonicotinoids. This partial and temporary ban seems incoherent. Logically, neonicotinoids substances should be permanently banned and under any conditions.
Literature review of Goulson on environmental risks caused by the use of neonicotinoids. Many interesting figures and bibliographic sources. GOULSON D., 2013. Review : An overview of the environmental risks posed by neonicotinoid insecticides. Journal of Applied Ecology, 50, 977-987.
Document containing most scientific studies until 2012 about the impact of neonicotinoids on bees. HOPWOOD J., VAUGHAN M., SHEPHERD M., BIDDINGER D., MADER E., HOFFMAN BLACK S., MAZZACANO C., 2012. Are neonicotinoids killing bees? A review of research into the effects of neonicotionoids insecticides on bees, with recommandations for action. The Xerces society for invertebrate conservation, 44p.
State of play of the current situation of bees and their disappearance, as well as potential causes. LEVEILLE, 2013. Bees, queens of survival. Inra, Science et Impact.
One of the few news articles that addresses the theme of wild pollinators:
MISEREY Y., 2013. Les insectes pollinisateurs vont très mal. Le Figaro.
Survey compiled by the government website about the disappearance of bees. SCIENCE.GOUV.FR, 2008. The disappearance of bees: survey (Dossier Biologie / Sciences du vivant).
Inventory of losses of herds in the Midi-Pyrenees region conducted by the Association for the Development of Beekeeping in the Midi-Pyrenees. ADAM.ITSAP.ASSO.FR, 2014. Identify livestock losses: Summary of livestock losses during the last 3 winters in the Midi-Pyrenees.
Descriptions of the various families of wild bees and their lifestyle. VILLEMANT C., 2005. Nests of solitary and social bees. Insects, 137, 13-17.