Chronic Toxicities of Neonicotinoids to Nymphs of the Common New Zealand Mayfly Deleatidium spp.

Abstract

Neonicotinoid insecticides have been shown to have high chronic toxicity relative to acute toxicity, and therefore short‐term toxicity tests ≤96 h in duration may underestimate their environmental risks. Among nontarget aquatic invertebrates, insects of the orders Diptera and Ephemeroptera have been found to be the most sensitive to neonicotinoids. To undertake a more accurate assessment of the risks posed by neonicotinoids to freshwater ecosystems, more data are needed from long‐term tests employing the most sensitive taxa. Using nymphs of the common New Zealand mayfly genus Deleatidium spp., we performed 28‐d static‐renewal exposures with the widely used neonicotinoids imidacloprid, clothianidin, and thiamethoxam. We monitored survival, immobility, impairment, and mayfly moulting propensity at varying time points throughout the experiment. Imidacloprid and clothianidin exerted strong chronic toxicity effects on Deleatidium nymphs, with 28‐d median lethal concentrations (LC50s) of 0.28 and 1.36 µg/L, respectively, whereas thiamethoxam was the least toxic, with a 28‐d LC50 > 4 µg/L (highest concentration tested). Mayfly moulting propensity was also negatively affected by clothianidin (during 3 of 4 wk), imidacloprid (2 of 4 wk), and thiamethoxam (1 of 4 wk). Comparisons with published neonicotinoid chronic toxicity data for other mayfly taxa and larvae of the midge genus Chironomus showed similar sensitivities for mayflies and midges, suggesting that experiments using these taxa provide reliable assessments of the threats of neonicotinoids to the most vulnerable freshwater species. Environ Toxicol Chem 2019;38:2459–2471. © 2019 SETAC

Time-Cumulative Toxicity of Neonicotinoids: Experimental Evidence and Implications for Environmental Risk Assessments

“…Two of them used imidacloprid and the others thiamethoxam; data from another test could not be used (Table S1). The same finding applies to two tests using imidacloprid: one on the amphipod Gammarus pulex [34] and another on the midge Chironomus riparius [35]. A further test using thiacloprid on the caddisfly Notidobia ciliaris suggests the same pattern, as indicated by n = 0.91 despite the poor fit of the model to the data (r 2 = 0.47) [9].…”

Multiple Stressors in Aquatic Ecosystems: Sublethal Effects of Temperature, Dissolved Organic Matter, Light and a Neonicotinoid Insecticide on Gammarids

“…The present study, however, contrasts earlier studies reporting a reduction in molting rate, for instance, in cladoceran Daphnia magna (Qi et al 2013 ) or the mayfly Deleatidium spp. (Macaulay et al 2019 ) at higher concentrations of other neonicotinoids, namely guadipyr, imidacloprid, thiamethoxam and clothianidin. These contrasting effects point towards species- or neonicotinoid-specific effects in molting requiring further research to uncover the underlying mechanisms.…”

Physiological Effects of Neonicotinoid Insecticides on Non-Target Aquatic Animals—An Updated Review

“…Clothianidin and imidacloprid depicted persistent toxicity impact on Deleatidium nymphs with LC 50 at 28 d as 1.36 and 0.28 ppb, respectively, with thiamethoxam being lowest in toxicity with 28 d LC 50 > 4 ppb. The molting of mayfly was negatively affected by imidacloprid (2 of 4 weeks), thiamethoxam (1 of 4 weeks) and clothianidin (3 of 4 weeks) [52]. Further in an acute and chronic toxicity study with imidacloprid exposure to freshwater arthropods, it was observed that caddisfly and mayfly species were utmost sensitive to imidacloprid exposures in short-term, whereas, mayflies were most sensitive to imidacloprid (long-term).…”