Prevalence of neonicotinoid insecticides on MDC intensively managed wetland areas and surrounding landscapes with a focus on impacts to aquatic invertebrates
July 2015 - June 2019
- Missouri Department of Conservation
Neonicotinoids are a relatively new class of chemical insecticide widely used as pre-planting treatments on crop seeds to control insect agricultural pests. Recent concerns regarding the potential acute and chronic effects of these chemicals on bees and aquatic invertebrates have resulted in restrictions on their use in both Europe and Canada. In the United States, the EPA is currently reviewing the registered uses of these products. In addition to toxicity concerns regarding non-target species, these chemicals are relatively water soluble and persistent in soil, raising alarm about contamination of surface waters in the vicinity of their use (Goulson 2013). A recent study in the prairie pothole region of Canada (Main et al. 2014) revealed widespread occurrence of these insecticides in wetlands at water concentrations shown to be toxic to aquatic invertebrates in the laboratory. Given the emerging evidence for potential harm neonicotinoids have on multiple taxa, the immediate issue for MDC is to determine if use of neonicotinoid-treated seeds in association with agricultural activities on MDC properties result in concentrations of these insecticides in MDC wetlands at levels that result in ecological impairment, particularly to aquatic invertebrates. A related issue is the prevalence of neonicotinoids in the surrounding landscape and water sources and whether this results in concentrations on MDC properties that have detrimental effects to aquatic invertebrates. Neonicotinoids are systemic insecticides that translocate an active ingredient throughout a growing plant and act on the nervous system of insects that feed on the plant (Syngenta 2011). Neonicotinoids were developed in the 1980s and have been widely adopted for agricultural use throughout North America and Europe, in large part because they are selectively more toxic to insects than vertebrates (Kollmeyer et al. 1999, Tomozawa and Casida 2005). Active ingredients used in neonicotinoid-formulated insecticides include acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam (Goulson 2013). Imidacloprid, clothianidin, and thiamethoxam, used as seed treatments for corn and soybeans as well as a number of other agricultural crops, fruits, and vegetables, are three of the most commonly used active ingredients; imidacloprid is also widely used in lawn and garden products as well as topical flea applications (Hladik et al. 2014). Use of neonicotinoids has increased considerably since 2000 due to their low toxicity to vertebrates, high toxicity to insects, flexible use, and systemic activity (Goulson 2013). Currently, the vast majority of corn seed planted in the Midwest is treated with either clothianidin or thiamethoxam while soybean seeds are treated with thiamethoxam (Krupke et al. 2012). All three have been implicated in honey bee deaths (Krupke et al. 2012, Mason et al. 2013) while imidacloprid has been linked to reduced colony growth and queen performance in bumble bees (Whitehorn et al. 2012). This has raised concerns about potential detrimental effects on bee populations, specifically, and pollinator populations, in general. The Environmental Protection Agency (EPA), although not currently banning or restricting the use of the neonicotinoid pesticides, is conducting a registration review on imidacloprid due to uncertainty regarding potential chronic effects on pollinators as well as other taxa including avian species, small mammals, and aquatic invertebrates (EPA 2008). A benefit of neonicotinoids is that application rates are low and precise; when applied as a seed dressing, rates typically range from 0.25 to 1.25 mg a.i./seed. However, >90% of active ingredients found in neonicotinoids applied as seed treatments enter the soil, where half-life can range from 200 to >1000 days (Goulson 2013). Given the relatively long half-life and high degree of water solubility of many neonicotinoids, repeated application has the potential to accumulate high concentrations in soils, which can then leach to groundwater or surface water following precipitation events (Gupta et al. 2008, Starner and Goh 2012). Recently, neonicotinoids were detected in >90% of wetlands sampled within the prairie pothole region of Saskatchewan (Main et al. 2014), while Hladik et al. (2014) reported neonicotinoid occurrence in all Midwestern streams sampled, many with concentrations exceeding acute and chronic exposure levels for aquatic macroinvertebrates. Neonicotinoids are highly toxic to aquatic invertebrates (Bayer CropScience 2010, Syngenta 2006), which are a major source of protein for many wetland dependent species, particularly migratory water birds (Rundle and Sayre 1983, Krapu and Reinecke 1992, Skagen and Oman 1996, Davis and Smith 1998). Beketov et al. (2008) demonstrated that a single pulse application of the neonicotinoid thiacloprid altered long-term community structure of stream macroinvertebrates in a mesocosm, with populations of longer-lived species less likely to recover. A study in the Netherlands reported a significant negative correlation between imidacloprid concentrations in surface waters and macroinvertebrate abundance, including orders Diptera and Ephemeroptera, which commonly occur in wetland ecosystems ((Van Dijk et al. 2013). However, this study relied on disparate, previously collected data, where invertebrate and neonicotinoid samples were collected in different locations (up to 1 km apart) and times (up to 160 days apart) (Van Dijk et al. 2013) Prolonged exposure in water to the neonicotinoid imidacloprid was linked to changes in growth, persistence and community composition of aquatic invertebrates, particularly to individuals in the functional group known as shredders, potentially reducing ecosystem functions related to decomposition, nutrient cycling and water quality (Kreutzweiser et al. 2009, Agatz et al. 2014, Chagnon et al. 2014). Additionally neonicotinoids are speculated to have indirect effects on wetland ecosystems through the ability to alter the base of aquatic food webs and reduce availability of important invertebrate prey for wetland dependent taxa (Chagnon et al. 2014). In a mesocosm experiment, annual application of two systemic insecticides, imidacloprid and fipronil, reduced benthic arthropod prey, and led to a reduction in fish growth rates (Hayasaka et al. 2012). Several recent studies have speculated that declines of many insectivorous bird species are linked to high application rates of neonicotinoids in the surrounding landscape and subsequent reductions to invertebrate prey base (Mason et al. 2013). Indeed, Hallmann et al. (2014) recently reported a negative correlation between local population trends of insectivorous birds and neonicotinoid concentrations in surface waters, and attributed the relationship to cascading trophic effects of neonicotinoids to aquatic food chains. Given the high use of neonicotinoid insecticides as a pre-planting treatment of corn and soybean seeds in the Midwest and their inherent characteristics, i.e., acute toxicity to insects, relatively long half- lives in soil, and high water solubility, that result in potentially deleterious effects, either directly or indirectly, on numerous taxa, it is imperative to determine if these chemicals are present in Missouri wetlands either due to direct application (i.e., planting treated seeds) or through surface water or ground water runoff or other means of transport, in concentrations that may cause harm to beneficial, non-target aquatic invertebrates and other taxa.