Physiological and behavioural effects of imidacloprid on two ecologically relevant earthworm species (Lumbricus terrestris and Aporrectodea caliginosa)

Abstract

Earthworms play key roles in soils and sub-lethal effects of environmental toxicants on these organisms should be taken seriously, since they might have detrimental effects on higher ecological levels. In laboratory experiments we have assessed sub-lethal effects (body mass change and cast production) 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. Changes in cast production, a new biomarker previously validated using L. terrestris, was assessed by soil sieving using the recommended mesh size (5.6 mm) for L. terrestris and three different mesh sizes for A. caliginosa (5.6, 4 and 3.15 mm). The 4 mm mesh size proved to be the most suitable sieve size for A. caliginosa. Cast production increased by 26.2% in A. caliginosa and by 28.1% in L. terrestris at the lowest imidacloprid concentration tested (0.2 mg kg(-1) dry soil), but significantly decreased at higher concentrations (equal to and above 0.66 mg kg(-1) dry soil) in both earthworm species after the 7 days exposure experiment. These decreases in cast production ranged from 44.5 to 96.9% in A. caliginosa and from 42.4 to 95.7% in L. terrestris. The EC(50) for cast production were 0.84 (L. terrestris) and 0.76 mg kg(-1) dry soil (A. caliginosa), 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. The biomarkers used in the present study, body mass change and changes in cast production, may be of ecological relevance and have shown high sensitivity for imidacloprid exposure of earthworms. The measurement of changes in cast production should be considered for inclusion in current standard tests.

Sensitivity of Eisenia fetida in comparison to Aporrectodea caliginosa and Lumbricus terrestris after imidacloprid exposure. Body mass change and histopathology

“…insecticide in agriculture worldwide, but it is known that this practice cause negative effects on non-target organisms (Capowiez et al 2003(Capowiez et al , 2005Dittbrenner et al 2010Dittbrenner et al , 2011aKreutzweiser et al 2009;Luo et al 1999;Mostert et al 2002). As earthworms contribute to a great extent to soil function, i.e.…”

“…Body mass change-as an integral part of the acute and chronic standard tests-is well established in toxicity testing and can sensitively indicate stress in earthworms (Capowiez and Bérard 2006;Dittbrenner et al 2010;Gomez-Eyles et al 2009;Olvera-Velona et al 2008;Zwahlen et al 2003). Without clearing the earthworms intestines prior weighing, body mass change can be interpreted as an indicator of earthworm activity (filling of the intestine) Dittbrenner et al 2010).…”

“…Without clearing the earthworms intestines prior weighing, body mass change can be interpreted as an indicator of earthworm activity (filling of the intestine) Dittbrenner et al 2010). Since there is a link between earthworm activity and soil quality, this biomarker is of high ecological relevance.…”

Ecological Impacts of Insecticides

“…Replacement of those broad-spectrum insecticides with pyrethroids such as -cyhalothrin has practically no impact on tropical earthworm populations because the latter class of insecticides is less toxic to earthworms (Table 2). Neonicotinoids are also safer to these organisms, but sublethal effects on earthworm burrowing activity have been observed after application of imidacloprid at 0.5-1.0 mg/kg in soil (Capowiez et al 2006), as well as significant weight losses and 44-97% less cast production within the typical range 0.33-0.6 mg/kg of this insecticide in soil (Dittbrenner et al 2010). Weight loss and cocoon production among earthworms are also seriously affected when concentrations of imidacloprid in the litter of treated forests exceed 3 mg/kg (Kreutzweiser et al 2008).…”

Evaluation of Earthworms Present on Natural and Agricultural-Livestock Soils of the Center Northern Litoral Santafesino, República Argentina

“…Stress generated from lambda-cyhalothrin exposure had a lower impact over A. trapezoides (endogeic) than in E. fetida (epigeic) that could be explained by the fast reaction associated to ingestion/egestion rate of epigeic earthworms as a consequence of their direct contact with the pesticide [7,102,[104][105][106][107][108][109][110][111]. Researches performed by Cerón Rincón & Melgarejo Muñoz [112] and Renella et al [113] registered stress symptoms at the microfloral, microbial and enzymatic activities which could explain the results of the higher exposure concentrations (6 and 8 mg.kg -1 ).…”