Abstract
Neonicotinoid insecticides have come under increasing scrutiny for their impact on non-target organisms, especially pollinators. The current scientific literature is mainly focused on the impact of these insecticides on pollinators and some aquatic insects, leaving a knowledge gap concerning soil invertebrates. This study aimed at filling this gap, by determining the toxicity of imidacloprid and thiacloprid to five species of soil invertebrates: earthworms (Eisenia andrei), enchytraeids (Enchytraeus crypticus), Collembola (Folsomia candida), oribatid mites (Oppia nitens) and isopods (Porcellio scaber). Tests focused on survival and reproduction or growth, after 3–5 weeks exposure in natural LUFA 2.2 standard soil. Imidacloprid was more toxic than thiacloprid for all species tested. F. candida and E. andrei were the most sensitive species, with LC50s of 0.20–0.62 and 0.77 mg/kg dry soil for imidacloprid and 2.7–3.9 and 7.1 mg/kg dry soil for thiacloprid. EC50s for effects on the reproduction of F. candida and E. andrei were 0.097–0.30 and 0.39 mg/kg dry soil for imidacloprid and 1.7–2.4 and 0.44 mg/kg dry soil for thiacloprid. The least sensitive species were O. nitens and P. scaber. Enchytraeids were a factor of 5–40 less sensitive than the taxonomically related earthworm, depending on the endpoint considered. Although not all the species showed high sensitivity to the neonicotinoids tested, these results raise awareness about the effects these insecticides can have on non-target soil invertebrates.
Highlights
Neonicotinoids are neuroactive insecticides which act on nicotinic acetylcholine receptors on the post synaptic membrane, disrupting neural transmission in the central nervous system of insects (Tomizawa and Casida 2003, 2005)
The aim of this study was to investigate the toxicity of imidacloprid and thiacloprid to five species of soil invertebrates—the collembolan Folsomia candida, the oribatid mite Oppia nitens, the isopod Porcellio scaber; and two oligochaetes: the earthworm Eisenia andrei and the enchytraeid Enchytraeus crypticus
This study shows that: 1. F. candida and E. andrei were the most sensitive species to both neonicotinoids, enchytraeids and isopods showing intermediate sensitivity, and the oribatid mite O. nitens being relatively insensitive (Table 1); 2
Summary
Neonicotinoids are neuroactive insecticides which act on nicotinic acetylcholine receptors (nAChR) on the post synaptic membrane, disrupting neural transmission in the central nervous system of insects (Tomizawa and Casida 2003, 2005) This can lead to sub-lethal effects, such as paralysis or even the death of the animal (Simon-Delso et al 2015). Apart from seed dressing, these insecticides can be used as soil treatments and foliar spray (Jeschke et al 2011), soil drench, irrigation water and trunk injection (Goulson 2013) Due to their broad application methods and persistence in soil, different species of non-target organisms can be affected, involving different routes of exposure (pore water, food or skin contact)
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