Since their introduction in the 1990s, neonicotinoids have become the most common insecticides, making up 24 per cent of the global market in 2011. In the UK, they are commonly applied to crops such as oilseed rape, maize and cereals as seed coatings before planting. Although this has met technical and commercial goals, there is growing evidence of harmful effects to non-target organisms, namely bee species and other pollinators.
Neonicotinoids are broad spectrum, water soluble, systemic insecticides. The active compound within them accumulates in plant tissue, increasing their efficiency at killing a large range of insect pests. Their application to soil or seeds ensures integration into the whole plant tissue, including the nectar and pollen of flowering plants. If ingested, this can have sublethal effects on some pollinators such as honeybees, bumblebees and butterflies.
Their mechanism involves selectively acting on the insect’s central nervous system, as an agonist of nictotinic acetylcholine receptors, a neurotransmitter. This can cause paralysis and eventually death, when ingested at lethal and sub-lethal concentrations.
Neonicotinoids are favoured pesticides as they have little toxicological risk to subsequent human consumers. They show little to no binding affinity to mammalian nictotinic acetylcholine receptors due to fundamental structural differences.
Many scientists believe further EU restrictions on neonicotinoids will have detrimental effects such as pest resistance and decreased yields.“If groups of chemistries are limited by legislation”, says a Rothamsted Research statement, “the remaining groups will be more widely used, resulting in an increased risk of pests developing resistance.”
Neonicotinoids aren’t exclusively used for agricultural purposes, but also in urban pest and veterinary ecto-parasitic control. They are extremely common; imidacloprid is used in over 120 countries, making it the most widely used pesticide in the neonicotinoid family.
However, questions remain over their impact on off-target species. Some research has shown that neonicotinoids can impair brain tissue function and development in bees, creating navigation issues and memory loss. Much of the laboratory and semi-field research has shown that neonicotinoids can reduce the number of offspring and foraging ability of bumblebees, causing a reduction in colony size.
Consequences for honeybees can be similar, and can contribute to colony collapse as worker bees get lost or die whilst foraging. Some studies suggest neonicotinoids affect bumblebees, with honeybees unaffected, and short term field research suggests exposure to neonicotinoids has no effect on either honeybee or bumblebee colonies.
However, with a limited time frame, neonicotinoids would not have spread sufficiently through the environment. Laboratory experiments are also unreliable as they inaccurately represent natural concentrations and bee interactions.
It is not recent news that bee populations are in decline. With increased demand for food comes stress on greater yields, and increased land for crop growth. This subsequently causes habitat fragmentation, making it difficult for bee populations to travel between suitable areas, and hurting wildflowers that bees feed from.
But pesticides are far from the only culprit; diseases transferred by parasitic mites, climate change and malnutrition also play a part. This is not good; insect pollinators are estimated to support 9.5 per cent of global food production, playing a vital role in the health and diversity of natural plant species and crops, ensuring genetic information is passe between habitats, driving genetic diversity. With a crucial role in pollinating food crops, bees contribute to the UK economy.
Restricting neonicotinoid use may be the safest option until more evidence, applicable to natural ecosystems, is available. It is in the hands of policy makers to decide on an alternative means of pest eradication, and whether this change is worth risking decreases in yield production. “It will be very difficult, if not impossible, to maintain production of many crops if neonicotinoids are more widely restricted or banned completely.”