Pollinators are vital to the natural environment and economy in the UK, providing services worth over £440 million per year. Recent declines in their numbers and health are concerning, and evidence linking neonicotinoid pesticide use with these has prompted further action and discussion amongst many groups.
On 12th February, the all-party parliamentary group on agroecology met to discuss these issues, focusing on how the countryside can be managed to maximise the number and diversity of pollinators and other insects. The meeting was chaired by Caroline Lucas MP, with presentations from Professor Dave Goulson – Stirling University, Dr Nigel Raine – Royal Holloway University London (RHUL), and Dr Mark Brown – RHUL.
The declines in wildlife observed across many habitats for a number of years were highlighted by Dave Goulson. Bees have suffered as a part of these, and are facing increased losses around the world in the future. Although policy decisions can explain the declines in biodiversity in the UK from 1945-1990, their continuation into recent decades is puzzling, especially with the implementation of agri-environment schemes to boost biodiversity. Habitat loss and fragmentation through altered woodland or farmland management are not the only environmental stressors that can affect the abundance and diversity of insects, however. Pests and diseases, climate change, and pesticides are also key factors.
Neonicotinoid pesticides are the most widely used series of insecticides in the world, and have been used increasingly since the 1980s in the UK. Dave Goulson highlighted the exposure that bees and other insects may receive to these pesticides. As neonicotinoids are applied to seeds, rather than sprayed onto plants, they have a systemic coverage, and are present in pollen and nectar. Application of the pesticide through a seed coating does not necessary isolate the pesticide to the plant, with problems of leakage into the wider environment still present. Only 2% of the pesticide remains in the plant, with 1% blowing off as dust when the seed is sown, and 97% moving into the soil.
The small amounts of dust blown away from seeds can still have an effect on bees and other insects, as highlighted by lethal dosage testing. To assess the lethal levels of pesticides, LD50 is used. This is the dosage level that kills 50% of a sample population. For one neonicotinoid, imidacloprid, the LD50 is 177mg for rats, and 5mg for partridges. For honeybees, it is 4ng – that’s 0.0000004mg. As bees are lighter and smaller than partridges and rats, it would be expected that they would be more sensitive to dosages. However, although partridges are 1000 times heavier than bees, the LD50 for honeybees is a million times lower than for partridges. This makes imidacloprid 1000 times more toxic to bees than to partridges. Imidacloprid is the most studied neonicotinoid, so the effects of others in the group are not widely known.
The presence of neonicotinoids in soil is also concerning, as they can take a long time to degrade. The half life of neonicotinoids is approximately 200-500 days, with some studies showing half lives of more than 1000 days. The use of neonicotinoids in consecutive years could lead to the accumulation of pesticides in the soil, exposing pollinators to even higher levels. This was demonstrated in the Draft Assessment Report for Imidacloprid in 2006. After applying imidacloprid year on year, the levels of pesticide were assessed before each sowing. Despite accumulations of 50-60 parts per billion (10 ppb is considered a lethal level), regulators of the product concluded that “the compound has no potential for accumulation in soil.”
The effects of pesticides to the behaviour and ecology insect pollinators were outlined by Nigel Raine. Generally, pesticides act on the nervous systems of insects. Small changes here can have huge consequences on physiology and behaviour. Studies using a number of pesticides in both field and lab conditions have demonstrated their detrimental effects on walking, grooming, feeding, learning, homing and foraging. There are also effects on colony function for social bees – honey bees and bumblebees – as demonstrated in a seminal paper in Science last year, where exposure to neonicotinoids resulted in an 85% reduction in queen production.
All speakers emphasised that pesticides are just one of many stressors that can affect bees, and that these can have both additive and multiplicative effects. Pests and diseases pose great threats to species across all groups in the UK, and Mark Brown highlighted this threat for insect pollinators. Bee diseases such as deformed wing virus are already present in the UK, and future threats include trypanosomes and tracheal mites. One of the main pathways for bee disease in the UK is through the import of bees and other insects, some of which are used in integrated pest management. Current management of emergent diseases for bees is dealt with by the National Bee Unit, as part of FERA, but Mark highlighted the need for screening of imports and a national assessment of emergent diseases. A project is currently underway for the latter, with the mapping of two diseases in the UK honey bee and bumblebee populations. This type of work enables the prevalence, impact, and distribution of threats to the UK bee population to be assessed.
This meeting was relevant and timely, and highlighted the need and potential of the Environmental Audit Committee’s Inquiry into Insects and Insecticides. The final evidence sessions for this inquiry are underway, and the report is likely to be published in early March. Europe’s Food Safety Authority concluded last month that neonicotinoids pose unacceptable risks to bees, and as highlighted in our previous blog, there is sufficient evidence to put a small-scale or short-term ban of neonicotinoid pesticides in place under the precautionary principle guidelines. It may not just be pesticides that are affecting bee health and abundance, but the removal of this stressor could have huge effects.