Algemeen

In “Silent Spring”, Rachel Carson gave society a warning about the dangers of organochlorine insecticides such as DDT or dieldrin: “These sprays, dusts, and aerosols are now applied almost universally to farms, gardens, forests, and homes - non-selective chemicals that have the power to kill every insect, the "good" and the "bad", to still the song of birds and the leaping of fish in the streams, to coat the leaves with a deadly film, and to linger on in soil - all this, though the intended target may be only a few weeds or insects. Can anyone believe it is possible to lay down such a barrage of poisons on the surface of the earth without making it unfit for all life?.” The situation is not much different today. Wild pollinators and honeybees alike have been facing an increasingly toxic landscape since the introduction and rapid uptake of neonicotinoids in the late 1990s. Mining data from USDA, EPA, industry and California's pesticide use reporting system (the only one of it's kind), here's a snapshot of what bees are facing in the field:
- Over 2 million pounds of clothianidin, imidacloprid and thiamexotham (three neonicotinoids) are used in an average year.
- At least 143 million of our 442 million acres of cropland is planted with crops treated with one of three neonicotinoids: clothianidin, imidacloprid and/or thiamexotham.
- 83+ million of these acres are corn, upon which honeybees rely for core nutrition (corn is wind pollinated, it doesn't need bees for pollination, but its sheer abundance of pollen makes it a staple source of bee forage).

Imidacloprid is a systemic insecticide effective in controlling the exotic pest Adelges tsugae (hemlock woolly adelgid) in eastern hemlock (Tsuga canadensis) trees. Concerns over imidacloprid impacts on nontarget species have limited its application in southern Appalachian ecosystems. We quantified the movement and adsorption of imidacloprid in forest soils after soil injection in two sites at Coweeta Hydrologic Laboratory in western North Carolina. Soils differed in profile depth, total carbon and nitrogen content, and effective cation exchange capacity. We injected imidacloprid 5 cm into mineral soil, 1.5 m from infested trees, using a Kioritz soil injector. We tracked the horizontal and vertical movement of imidacloprid by collecting soil solution and soil samples at 1 m, 2 m, and at the drip line from each tree periodically for 1 yr. Soil solution was collected 20 cm below the surface and just above the saprolite, and acetonitrile-extractable imidacloprid was determined through the profile. Soil solution and extractable imidacloprid concentrations were determined by high-performance liquid chromatography. Soil solution and extractable imidacloprid concentrations were greater in the site with greater soil organic matter. Imidacloprid moved vertically and horizontally in both sites; concentrations generally declined downward in the soil profile, but preferential flow paths allowed rapid vertical movement. Horizontal movement was limited, and imidacloprid did not move to the tree drip line. We found a negative relationship between adsorbed imidacloprid concentrations and soil microarthropod populations largely in the low-organic-matter site; however, population counts were similar to other studies at Coweeta.

In this study, we used two different types of bioassay, a contact filter paper toxicity bioassay and a soil toxicity bioassay, to compare the acute toxicity of twenty-four insecticides belonging to six chemical categories on earthworm species, Eisenia fetida. It was concluded that irrespective of bioassay systems, earthworms were more susceptible to neonicotinoids than to other modern synthetic insecticides.

Earthworms play key roles in soils and sublethal effects of environmental toxicants on these organisms should be taken seriously, since they might have detrimental effects on higher ecological levels. Earthworms make important contributions to the breakdown of organic matter, soil fertility, and to the formation of soils. In laboratory experiments we have assessed sub-lethal effects of imidacloprid on two earthworm species commonly found in different agricultural soils (Lumbricus terrestris and Aporrectodea caliginosa). After 7 days of exposure in contaminated soil, a significant loss of body mass was found in both species exposed to imidacloprid concentrations as low as 0.66 mg kg-1 dry soil. These losses ranged from 18.3 to 39% for A. caliginosa and from 7.4 to 32.4% for L. terrestris, respectively. The detected sub-lethal effects were found close to the predicted environmental concentration (PEC) of imidacloprid, which is in the range of 0.33–0.66 mg kg-1 dry soil.