No one likes pests: mosquitoes at your barbeque, termites in your basement, caterpillars on your garden vegetables and field crops. In the past 70 years, the chemical industry has developed a remarkably effective arsenal of chemicals designed to kill pests. DDT was among the first. Organophosphate insecticides soon followed. Now, insecticides in the family of neonicotinoid compounds are under great scrutiny, with billions of profits at stake for Bayer and Syngenta if these insecticides are outlawed.
Let’s not forget that pesticides are designed to kill things, usually by interfering with the natural physiology of the pest in question. Since many organisms share common physiology, it is not surprising that there are collateral effects. The DDT molecule mimics endocrine compounds, so it should not surprise us that DDT disrupted egg-shell development and reproductive success in birds. When DDT was banned, pelicans, ospreys and eagles recovered in the lower 48 states. For the Northern Gannet, residues of DDT have dropped more than 99% from 1969 to 2009, and reproductive success has increased markedly (Champoux et al. 2015).
DDT is implicated as a carcinogen for humans, but the case remains equivocal (Eskenazi et al. 2009). Still, there are those who believe that there is no connection between DDT and bird decline and no harm of DDT to humans. In some tropical countries, DDT is still used to fight malaria mosquitoes, since its risk to humans is thought to be less than that of malaria. When birds and other species are killed as a result of collateral damage by pesticides, we should heed the warning for humans, since we are often at the top of the food chain. Long-term low-level effects take decades to manifest.
Soon after it was in widespread use, certain insects were observed to be resistant to DDT. This was natural selection in action, for a small number of resistant individuals were able to multiply abundantly in the absence of competition with their common neighbors. Resistance to DDT begged for the development of more virulent and effective insecticides, including organophosphates and neonicotinoids.
Neonicotinoids are now among the most important insecticides protecting cereal and other crops from insect attack. Unfortunately, these compounds have been widely implicated in the collateral decline of another group of insects—bees. Insect pollinators are essential to the success of a wide variety of crops, including almonds, apples and blueberries, accounting for an estimated $15 billion in agricultural profits each year. What is good for cereal crops may not be good for fruits and nuts.
When neonicotinoids are used to coat seeds, the pesticide is then found at low levels throughout the plant as it grows. When crops are grown from neonicotinoid-treated seeds, the density and number of wild bees decline (Rundlof et al. 2015). Whether or not this effect accounts for the widespread decline in honey bees is unknown, but I am certainly suspicious of the correlation.
With the challenge of feeding 7 billion humans globally, and the prospect of that number increasing to 10 billion by mid-century, we need to think of something better than an escalating war between insecticides, the evolution of resistant insects, collateral damage, human toxicity and corporate profits. Organic farming may be one solution, but its lower crop yields per unit of land require the clearing of larger areas to maintain current production. Genetically-modified, resistant crop varieties may be another solution, provided we can show that the residual tissues of these plants have minimal effects on nature.
Several European countries have placed a moratorium on new uses for neonicotinoids. Recently, the Obama administration recommended further study of the problem in the U.S., and planting of 7 million acres of wildflowers to help restore and maintain bee populations. We cannot be proud of this shallow response in the face of solid science showing effects of neonicotinoids on bees. Have we not learned anything from our lessons with DDT?
Chagnon, M., D. Kreutzweiser, E.A.D. Mitchell, C.A. Morrissey, D.A. Noome and J.P. van der Sluijs. 2015. Risks of large-scale use of systemic insecticides to ecosystem functioning and services. Environ. Sci. Pollution Research 22: 119-124.
Champoux, L., J.-F. Rail, R.A. Lavoie, and K.A. Hobson. 2015. Temporal trends of mercury, organochlorines and PCBs in northern gannet (Morus bassanus) eggs from Bonaventure Island, Gulf of St. Lawrence, 1969-2009. Environmental Pollution 197: 13-20.
Eskenazi B, Chevrier J, Rosas LG, Anderson HA, Bornman MS, Bouwman H, Chen A, Cohn BA, de Jager C, Henshel DS, Leipzig F, Leipzig JS, Lorenz EC, Snedeker SM, Stapleton D 2009. The Pine River statement: human health consequences of DDT use. Environmental Health Perspectives 117 (9): 1359-67.
Goulson, D. 2014. An overview of the environmental risks posed by neonicotinoid insecticides. Journal of Applied Ecology 50: 977-987.
Rosi-Marshall, E.J., et al. 2007. Toxins in transgenic crop byproducts may affect headwater stream ecosystems. Proceedings of the National Academy of Sciences 104: 16204-16208.
Rundlof, M., G.K.S. Andersson, R. Bommarco, I. Fries, V. Hederstrom, L. Hebertsson, O. Jonsson, B.K. Klatt, T.R. Persersen, J. Yourstone and H.G. Smith. 2015. Seed coating with a neonicotinoid insecticide negatively affects wild bees. Nature 521: 77-80.