Abstract
In a recent study, we showed that the springtail Folsomia candida was quite sensitive the neonicotinoid insecticides imidacloprid and thiacloprid. This study aimed at determining the toxicity of both compounds to F. candida following exposure over three generations, in natural LUFA 2.2 standard soil. In the first generation, imidacloprid was more toxic than thiacloprid, with LC50s of 0.44 and 9.0 mg/kg dry soil, respectively and EC50s of 0.29 and 1.5 mg/kg dry soil, respectively. The higher LC50/EC50 ratio suggests that thiacloprid has more effects on reproduction, while imidacloprid shows lethal toxicity to the springtails. In the multigeneration tests, using soil spiked at the start of the first generation exposures, imidacloprid had a consistent effect on survival and reproduction in all three generations, with LC50s and EC50s of 0.21–0.44 and 0.12–0.29 mg/kg dry soil, respectively, while thiacloprid-exposed animals showed clear recovery in the second and third generations (LC50 and EC50 > 3.33 mg/kg dry soil). The latter finding is in agreement with the persistence of imidacloprid and the fast degradation of thiacloprid in the test soil.
Highlights
Neonicotinoids are widely used to protect crops against herbivorous insects, with application as seed-dressing agents (Tomizawa and Casida 2003; Douglas and Tooker 2015), soil treatment and spraying (Goulson 2013; Van der Sluijs et al 2015)
Neonicotinoids are systemic, being distributed throughout the plants via the sap stream, in this way making the entire plant toxic to, i.e., the target insects. They bind to nicotinergic acetylcholine receptors on the post-synaptic membrane of the neurons of insects
Concentrations measured after 28 days were 91.2–101% for the two lowest concentrations analysed (1.1 and 3.3 mg/kg dry soil), and 56.7% at 10 mg/kg
Summary
Neonicotinoids are widely used to protect crops against herbivorous insects, with application as seed-dressing agents (Tomizawa and Casida 2003; Douglas and Tooker 2015), soil treatment and spraying (Goulson 2013; Van der Sluijs et al 2015). Neonicotinoids are systemic, being distributed throughout the plants via the sap stream, in this way making the entire plant toxic to, i.e., the target insects. They bind to nicotinergic acetylcholine receptors (nAChR) on the post-synaptic membrane of the neurons of insects. Exposed animals show signs of disorientation and paralysis, from which they eventually die (Buckingham et al 1997; Goulson 2013; Matsuda et al 2001; Millar and Denholm 2007; Sheets 2001; Tomizawa and Casida 2003)
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