Bird decline, insect decline and neonicotinoids

As an aid to testing hypotheses for the causes of colony failure we have developed a compartment model of honey bee colony population dynamics to explore the impact of different death rates of forager bees on colony growth and development. The model predicts a critical threshold forager death rate beneath which colonies regulate a stable population size. If death rates are sustained higher than this threshold rapid population decline is predicted and colony failure is inevitable. The model also predicts that high forager death rates draw hive bees into the foraging population at much younger ages than normal, which acts to accelerate colony failure.

Compelling new evidence from the US government's top bee expert that modern pesticides may be a major cause of collapsing bee populations led to calls yesterday for the chemicals to be banned. A study published in the current issue of the German science journal Naturwissenschaften, reveals how bees given minute doses of the widely used pesticide imidacloprid became more vulnerable to infections from a deadly parasite, nosema. The study, led by Dr Jeffrey Pettis, the head of the US Department of Agriculture's Bee Research Laboratory, says: "We believe that subtle interactions between pesticides and pathogens, such as demonstrated here, could be a major contributor to increased mortality of honey bee colonies worldwide."

With three million Long Islanders dependent on a single underground aquifer for drinking water, local environmental groups have asked the State Department of Environmental Conservation to immediately ban the three most frequently found chemicals, atrazine, metalaxyl, and imidacloprid, from use on the Island. The D.E.C.’s own Long Island Pesticide Use Management Plan, issued in December, shows that imidacloprid was detected 782 times at 182 locations on Long Island, metalaxyl 1,292 times at 727 locations, and atrazine 126 times at 88 locations.

Research published this month in the online edition of the Bulletin of Environmental Contamination and Toxicology finds that the neonicotinoid pesticide imidacloprid contaminates surface waters in agricultural regions. Researchers at the California Department of Pesticide Regulation collected 75 surface water samples from three agricultural regions of California and analyzed them for contamination with imidacloprid. Samples were collected during California’s relatively dry-weather irrigation seasons in 2010 and 2011. Imidacloprid was detected in 67 samples (89%); concentrations exceeded the U.S. Environmental Protection Agency’s (EPA) chronic invertebrate Aquatic Life Benchmark of 1.05 μg/L (micrograms per liter) in 14 samples (19%). Concentrations were also frequently greater than similar toxicity guidelines developed for use in Europe and Canada. A benchmark is a chemical concentration, specific to either water or sediment, above which there is the possibility of harm or risk to the humans or animals in the environment.

Previously common farmland birds such as the corncrake, curlew and yellowhammer are now perilously close to extinction in Ireland, according to a four-year (2007-2011) study of the island’s bird populations. The corncrake Crex crex, whose distinctive cry used to be the bane of sleepless farmers, has seen its breeding population plummet by more than 80 per cent in the past 20 years alone. Breeding populations of curlew Numenius arquata are following a similar trajectory, down 60 per cent. The yellowhammer Emberiza citrinella has seen its numbers drop by more than 40 per cent in the past 20 years. One farmland bird which has already become extinct here is the corn bunting Miliaria calandra. This bird was recorded in modest numbers in the previous 1988-1991 Atlas survey but has since fallen off the radar.

A very important shift may be occurring in our understanding of pesticides: risk may increase over time, rendering even very small amounts of pesticides such as some nicotine-based neonicotinoids much more toxic than previously realized. Dutch researcher Dr. Henk Tennekes, with Dr. Francisco Sanchez-Bayo of Australia, have shown this in a new article in the Journal of Environmental & Analytical Toxicology: "Time-Dependent Toxicity of Neonicotinoids and Other Toxicants: Implications for a New Approach to Risk Assessment" that is an open-access research article downloadable with the link http://www.omicsonline.org/2161-0525/2161-0525-S4-001.pdf. Dr. Tennekes summarizes his deep concerns: "The article reviews a paradigm shift in the science of toxicology. The dose : response characteristics of neonicotinoid insecticides and certain metallic compounds turn out to be identical to those of genotoxic carcinogens, the most dangerous substances we know. Such poisons can have detrimental effects at any concentration level. Current pesticide risk assessment procedures are flawed and have failed to protect the environment. Regulators so far appear to be unwilling to accept this inconvenient truth. The powerful pesticide lobby does not want to face up to it either because the adoption of new risk assessment procedures would almost certainly lead to a ban on the money-spinning neonicotinoids, which are registered in more than 100 countries worldwide for use on more than 140 crops. They also have widespread applications in non-crop, including nursery, landscape, forestry, pest control and veterinary applications. Neonicotinoids are persistent and mobile in the soil and leach to ground water, and runoff to surface waters. Insects are now quietly but rapidly disappearing all over the globe, which will ultimately lead to collapse of the ecosystem and life as we know it. This is an ecological disaster that will affect us all, and that must be stopped."

We used LC/MS-MS to analyze samples of honey bees, pollen stored in the hive and several potential exposure routes associated with plantings of neonicotinoid treated maize. Our results demonstrate that bees are exposed to these compounds and several other agricultural pesticides in several ways throughout the foraging period. During spring, extremely high levels of clothianidin and thiamethoxam were found in planter exhaust material produced during the planting of treated maize seed. We also found neonicotinoids in the soil of each field we sampled, including unplanted fields. Plants visited by foraging bees (dandelions) growing near these fields were found to contain neonicotinoids as well. This indicates deposition of neonicotinoids on the flowers, uptake by the root system, or both. Dead bees collected near hive entrances during the spring sampling period were found to contain clothianidin as well, although whether exposure was oral (consuming pollen) or by contact (soil/planter dust) is unclear. We also detected the insecticide clothianidin in pollen collected by bees and stored in the hive. When maize plants in our field reached anthesis, maize pollen from treated seed was found to contain clothianidin and other pesticides; and honey bees in our study readily collected maize pollen. These findings clarify some of the mechanisms by which honey bees may be exposed to agricultural pesticides throughout the growing season. These results have implications for a wide range of largescale annual cropping systems that utilize neonicotinoid seed treatments.

Invertebrates are an essential food source for most farmland birds. Dvac suction sampling was used to determine the abundance, biomass and community composition of those invertebrate groups considered important in the diet of farmland birds for the commonest arable crops. Approximately 40 fields were sampled at the edge and mid-field over 2 years in three different locations in England. In cereals, the fauna was primarily comprised of Araneae (10%), Coleoptera (30%) and Hemiptera (58%), whereas the oilseed rape fauna was dominated by Coleoptera (65%) and peas and potatoes by Hemiptera (89%). Beans contained a high proportion of Coleoptera (39%) and Hemiptera (49%). Aphididae were the most abundant family (20–86% of total), although in oilseed rape and beans, Chrysomelidae, Curculionidae and Nitidulidae formed ca 20% of the fauna. Aphids only formed a small proportion (7%) of the total biomass, except in peas (32%). Instead, Araneae, Carabidae, Heteroptera, Homoptera and Tipulidae formed much larger and more equal proportions. The highest abundance and biomass of invertebrates were recorded in cereals and least in potatoes. The Grey Partridge chick-food index in all crops was only a half or less of the level required to ensure that chick survival is sufficient to maintain numbers of this red-listed species.

Pesticides have major indirect effects on birds via the killing of both invertebrates important for food and also agricultural weeds which provide seed resources and also cover for invertebrates. Several pieces of evidence support the negative relationship between insecticide spraying and vital rates of farmland bird populations. Probably the best example comes from a fully replicated study of the grey partridge (Perdix perdix L.). This study showed that pesticide spraying affected the invertebrate food of partridge chicks, which was correlated with chick survival, and was the main cause of population decline. More recent examples come from another farmland bird specialist, the yellowhammer (Emberiza citrinella). A study showed that arable fields sprayed during the summer were used less frequently than fields not sprayed during the summer by adult yellowhammers foraging for food for their young. The availability of arthropods was depressed up to 20 days after an insecticide spraying event and this negatively affected yellowhammer chick survival. Both herbicide spraying and fungicide spraying have also been shown to be negatively correlated with invertebrate populations and weed populations and so these are also likely to negatively affect farmland bird populations.

Birds are widespread, readily observed, feed at many levels of the food web, and are responsive to environmental change, making them good indicators of ecosystem health. Globally, over 150 species of birds have been lost since the 16th century and one in eight is currently threatened with extinction. Over the past 20 years, the status of the world’s birds has deteriorated, with more species moving closer to extinction. Of particular concern are declines in formerly common species. The last 20 years have witnessed a steady decline of bird species in terrestrial, freshwater, and marine ecosystems. Between 1988 and 2008, the status of 225 bird species was elevated to a higher level of risk.