Philip Strange considers the complex story of some popular insecticides
Late December is a low time of year for wild life, so I was surprised to see several fat, stripy bumblebees out foraging in both Dorset and in Devon when the weather allowed. According to the textbooks they should have been hibernating but I was interested to learn that one of our native bumblebees, the buff-tailed, sometimes keeps colonies going during the winter. Winter-flowering plants like mahonia and heather provide the pollen and nectar they need.
Having unexpectedly seen these insects going about their business, I was all the more saddened to read a report from the US about the mass killing of bumblebees in an Oregon supermarket car park. During the summer, the lime trees in the car park were colonised by aphids and these dropped sticky material, honeydew, on to parked cars. To deal with this tiresome problem, some enterprising individual decided to kill the aphids by spraying the lime trees with insecticide. What they failed to notice was that the trees were in flower, making them very attractive to bumblebees. The result of this unfortunate set of circumstances was that as many as 50,000 bumblebees ended up dead on the tarmac, the largest ever recorded loss of bumblebees.
The insecticide used to perpetrate this mass bee killing is one of a group of chemicals collectively known as neonicotinoids. These are relatively modern insecticides used very extensively in agriculture and in gardening for control of insect pests. For example, much of the oil seed rape grown in this country uses seed treated with these insecticides and many popular garden bug-killers are neonicotinoid-based. The neonicotinoids have the advantage that once applied to a crop, they are taken up systemically by the plant which then becomes poisonous to insects. There is concern that the poison will also be picked up by bees when they forage but the manufacturers say that the risk is low if the insecticides are used correctly. This includes not spraying crops when they are in flower and if bees are present.
Bees are very important for pollinating many of our crops and flowers. There had been worries for some time about a general decline in bee populations and although several contributory factors had been identified, including loss of habitat, pathogens and climate change, insecticides were also thought to be involved. Concerns about the effects of the neonicotinoids on bees intensified in 2012 when the results of field studies were released showing that at levels that did not directly kill bees, these insecticides impaired the survival of bee colonies and so could be contributing to the decline. These findings made the European Food Safety Authority take another look at the neonicotinoids and they came to the conclusion that safety testing on bees was incomplete for some of these chemicals. As a result, they recommended a two year moratorium on several agricultural uses of three of these insecticides. The prominent food retailer, Waitrose, took a wider view and asked all their suppliers of fruit, vegetables and flowers to phase out the three insecticides because of concerns about effects on bees, butterflies and other important pollinators.
Despite a groundswell of opinion against the insecticides in environmental groups, the UK government strongly opposed the ban on neonicotinoids, although it eventually had to follow the EU directive which came in to force in December 2013. The makers of the chemicals, Bayer and Syngenta, far from being contrite about the situation, have taken the European Commission to court over the decision and the National Farmers Union has backed the move. To be fair to the government, it has recognised that there is a problem for pollinators in the UK and is developing a National Pollinator Strategy to be implemented in 2014.
In the meantime there have been further indications of problems with these insecticides. Scientists in Japan had shown that the neonicotinoids might affect brain development in animals. Based on this and other work, the European Food Safety Authority decided that there was cause for concern and recommended that acceptable human exposure levels for some of these insecticides be reduced.
Studies in the Netherlands have shown that, following extensive use of the neonicotinoid insecticides in agriculture, they are contaminating ground water. The levels are high enough to kill invertebrates in ditches and in streams. Similarly, in Saskatchewan, prairie wetlands have been contaminated with the insecticides which may be killing midges and mosquitoes. The loss of these invertebrate species could have knock-on effects on birds that depend on them for food. The problem may be exacerbated by the persistence of the insecticides in soil. These are worrying observations and suggest that these chemicals are disturbing natural eco systems.
So, evidence is mounting that the neonicotinoids are endangering wildlife and particularly beneficial insects such as bees. Two opposing camps have emerged in this conservation battle. On one side is a wide range of environmental groups and campaign organisations who oppose the use of these insecticides. One the other side are the agrochemical companies and the farmers who want to see continued use.
What should we do? We should be aware of the effects of these chemicals on our environment and the effects they may have on pollinators. We should understand the arguments both in favour and against the use of these chemicals in agriculture. We should ask ourselves whether we really need to use these insecticides in our gardens especially if this results in the death of beneficial insects. Several prominent cities including Paris, Portland (Oregon), Seattle, Tokyo and Toronto have massively reduced pesticide use without any detrimental effects. Wouldn’t it be better if our gardens were insecticide-free and filled with bee-friendly flowers and bees?
Philip Strange is Emeritus Professor of Pharmacology at the University of Reading. He writes about how science fits in to society, hoping to bridge the gap between science and public understanding of science. His work may be read at http://philipstrange.wordpress.com/ and http://occamstypewriter.org/irregulars/