Neonicotinoids are Harmful to More Than Just Honeybees

Posted on: 27 April 2015

‘Neonicotinoids’ are synthetic insecticides that are less toxic to mammals than some other pesticides, and thus have become widely used. However, they are still toxic to non-target insects and, in 2013, the European Commission restricted their use on flowering crops attractive to bees. This decision was highly controversial, and unpopular with many farmers and manufacturers. The European Academies Science Advisory Council (EASAC), established to help European policy-makers deal more objectively and efficiently with scientific issues, formed a working group in 2013 to review the evidence for the impacts of neonicotinoid pesticides – not only bees – but on other pollinators and ecosystem service-providers as well. This working group, comprising 13 experts from across Europe, has just published its report (EASAC policy report 26, www.easeac.eu).

Jane Stout, Professor of Botany in the School of Natural Sciences, Trinity College Dublin, was the Royal Irish Academy nominee on the expert working group.

She said: “Although much of the debate so far has focussed on honeybees, this report highlights that there are much wider implications of neonicotinoid use. Of course it is not surprising that insecticides are toxic to insects – they are designed to be. The problem is that neonicotinoids are often applied as seed dressings, which dissolve in water, enter the plant as it grows, and exert toxic effects on insects that feed on the plant tissues. This includes sap-sucking or leaf-chewing pests, but also nectar- and pollen-feeding insects – not just honeybees, but also other bees, flies, beetles, moths and butterflies. In addition, once the insecticide is in the soil, it can enter non-crop plants growing adjacent to crops, such as herbaceous and woody hedgerow plants. As such, flower-visiting insects feeding on these can also be exposed. Natural enemies of crop pests can suffer through consumption of contaminated prey, soil organisms through consumption of contaminated organic matter, and aquatic organisms through neonicotinoids – which are water-soluble – finding their way into aquatic systems accidentally.

“Thus the range of organisms potentially exposed to neonicotinoids is far greater than just honeybees, which are quite resilient to the loss of individuals from their hives as colonies can contain several thousand bees and reproductive success depends on combined effort. Other organisms, including most other bee species, are less fortunate. Because many of these organisms provide services that are beneficial to farmers (such as pollination, natural pest control, soil formation, nutrient cycling, and soil carbon storage), and because they are part of the biodiversity of agricultural landscapes, there are much wider consequences of neonicotinoid use.

“There is now a large body of evidence from laboratory-based and natural field experiments, which demonstrates the negative impacts of neonicotinoids on a range of non-target organisms. For example, in a study published in the leading peer-reviewed journal Nature this week, we showed that bees (honeybees and large earth bumblebees) cannot taste low-concentrations of neonicotinoids in sugar solutions (see http://nature.com/articles/doi:10.1038/nature14414), and may actually prefer to forage on food containing neonicotinoids. Our findings imply that even if alternative food sources are provided for bees in agricultural landscapes where neonicotinoid pesticides are used, the bees may prefer to forage on the neonicotinoid-contaminated crops. Since neonicotinoids can also end up in wild plants growing adjacent to crops, they could be much more prevalent in bees’ diets than previously thought. Previous studies have suggested that exposure of this kind can affect bees’ fitness (i.e. their reproductive success), with potential knock-on negative impacts on bee populations.

“While farmers need to protect crops from pests that reduce their yields, the prophylactic use of neonicotinoids – such as using them as insurance measures against pest outbreaks – is inconsistent with the basic principles of Integrated Pest Management (IPM), where chemical control should only be used as a last resort. In addition, widespread use of pesticides which harm non-target organisms constrains the potential to restore biodiversity on farmland.

“What we need is a paradigm shift in agricultural pest control: this must include the reduced use of chemicals and the development of compounds and application methods that reduce exposing non-target, beneficial organisms to harm. Farmers need practical solutions so that they can farm in a way that doesn’t threaten organisms that provide essential ecosystem services and underpin agricultural sustainability.”

• This article was originally featured as an expert comment in the Irish Examiner, on Monday April 27th, 2015.
• To read more about Dr Stout’s research into neonicotinoid pesticides, see here.