3 years ago



Increasing neonicotinoid

Increasing neonicotinoid use is of particular concern to monarchs in the East because their main breeding range is coincident with the area of greatest neonicotinoid use in the Corn Belt. Seeds of other crops, such as cotton, which is a significant crop in many states where monarchs breed (including Texas, Arizona and California), are also now pre-treated with neonicotinoids. After leaving overwintering sites in Mexico, many first-generation monarchs breed in Texas, and thus quality and quantity of habitat in that state is extremely important to the size of the monarch population. Monarchs can be exposed to neonicotinoids in a variety of ways, and at different stages of their lifecycle. In brief, monarch adults can be exposed via direct contact with spray, residues on plants and other surfaces, particles released during the planting of treated seeds, contaminated water; and neonicotinoid-containing pollen, floral and extra-floral nectar and guttation liquid. Larvae can be exposed by direct contact with spray and residues, and also by eating milkweed tissues that have been contaminated, either by overspray or drift directly onto leaves, or by milkweed taking up insecticide from contaminated soil and/or water (Hopwood et al. 2012). In more detail, systemic movement of neonicotinoid insecticides increases the number of routes by which monarchs can be exposed. Neonicotinoids are taken up by plants and move through the vascular system to all tissues and organs, including flower buds, pollen, nectar, roots, leaves, and stems. They are then slowly metabolized within plant tissues, and some of the metabolites are also toxic; residues and metabolites kill insect pests for weeks, months, or sometimes for years (Oliver et al. 2010, Goulson 2013). Thus, if host milkweed plants take up neonicotinoids from adjacent treated crops (as described below), monarch larvae will be exposed. Adult monarch butterflies feed on a wide variety of flowering plants, and if they sip nectar or guttation liquids or eat pollen from treated plants, they can also be exposed to systemic neonicotinoids. As with most pesticides, only a fraction of neonicotinoid applications generally end up on or in targeted plants (Sur and Stork 2003, Goulson 2013), depending on the type of application. Also, a portion of neonicotinoids that does enter target plants is released into the environment as those plants decay. Environmental contamination with neonicotinoids occurs via several routes and thus poses risks to monarchs in different contexts: Neonicotinoids that do not contact or are not taken up by the plants during applications leach or run off directly into soil and water, where residues and metabolites can persist, remaining active for months to years (e.g. Huseth and Groves 2014). They regularly contaminate ground and surface waters near treated fields, impacting natural areas some distance from application sites at concentrations high enough to reduce insect populations (Mineau and Palmer 2013, Main et al. 2014). Monarchs can drink contaminated water, consume milkweed plants that have taken up neonicotinoids from contaminated soil and water, or drink nectar from a wide variety of plants that have taken up neonicotinoids from contaminated soil or water. Seed coatings form dust during planting as abraded seed tissues mix with talc or other carriers and are expelled from planting machines (Krupke et al. 2012, Tapparo et al. Monarch ESA Petition 96

2012, Nuyttens et al. 2013). This dust can contact monarch larvae and adults directly during the planting operation. Dust also settles on plants, soil and water in and around fields, where it can expose monarchs (both larvae and adults) after planting. Unharvested plant material from crops that have taken up neonicotinoids from foliar sprays, seed treatments, soil drenches, or other application methods contains residues and metabolites that can be released into soil (Hopwood et al. 2013) and water as the roots, stalks, and other plant parts decay, adding to environmental contamination. Given the widespread use of neonicotinoid insecticides, especially as seed treatments, it can be assumed that milkweeds and nectar plants in monarch habitats could be contaminated with neonicotinoids. According to Goulson (2013, p. 981): “Given their persistence and accumulation in soils, we might predict hedgerow plants and trees, field margin vegetation and naturally regenerating fallows to take up neonicotinoids.” Very low concentrations of neonicotinoids and other pesticides have been shown to cause sublethal effects in other insects. For example, studies show sub-lethal impacts of pesticides on bee species that include changes in foraging behavior, navigation ability, reduced reproduction, and many other processes (Blacquière et al. 2012, Bryden et al. 2013, Goulson 2013), as well as increased susceptibility to pathogens (Pettis et al. 2013). Sub-lethal effects of neonicotinoids on fruit flies include a disruption of mating behavior (Charpentier et al. 2014). These types of effects are of obvious relevance to monarch populations. Several studies suggest that levels of neonicotinoids in milkweed and nectar plants that have been exposed to contaminated soil, water, dust, or spray drift may reach concentrations that are toxic to monarchs in some situations, based on studies so far: The evidence presented here [in this review] suggests that the annually increasing use of neonicotinoids may be playing a role in driving these declines [of farmland insects and other taxa]. The concentrations accumulating in soil (1 to >100 ppb), waterways (often in excess of 1 ppb, sometimes up to 200 ppb), field margin plants (1–9 ppb) and nectar and pollen of flowering crops (1–50 ppb) exceed levels in crop tissues needed to control pest insects (5–10 ppb) and overlap with LC50 values for a range of non-target insects. They would appear to be sufficient to cause both direct mortality in the more sensitive nontarget species and chronic sublethal effects in many more. The groups most at risk are likely to include soil-dwelling insects, benthic aquatic insects, granivorous vertebrates and pollinators. Herbivorous insects feeding on field margin and hedgerow plants may also be exposed (Goulson 2013, p. 985). Monarchs are in the “pollinator” risk category as adults, and the “herbivorous insects feeding on field margin and hedgerow plants” risk category as larvae. Milkweeds have largely been eradicated from corn and soybean fields, but thelands enrolled in the Conservation Reserve Program and roadsides where common milkweed now hosts most monarch larvae and where nectaring occurs are largely within agroecosystems where neonicotinoids are widely used. Monarch ESA Petition 97

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