Dataset for: CHRONIC TOXICITIES OF NEONICOTINOIDS TO NYMPHS OF THE COMMON NEW ZEALAND MAYFLY DELEATIDIUM SPP.

Neonicotinoid insecticides have been shown to have high chronic relative to acute toxicity, therefore short-term toxicity tests of ≤ 96 hours in duration may underestimate their environmental risks. Among non-target aquatic invertebrates, insects of the orders Diptera and Ephemeroptera have been found to be the most sensitive to neonicotinoids. To undertake more accurate assessment of the risks posed by neonicotinoids to freshwater ecosystems, more data are needed from long-term tests using the most sensitive taxa. Using nymphs of the common New Zealand mayfly genus Deleatidium spp., we performed 28-day 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 to Deleatidium nymphs, with respective 28-day LC50s of 0.28 and 1.36 µg/L, while thiamethoxam was the least toxic, with a 28-day LC50 > 4 µg/L (highest concentration tested). Mayfly moulting propensity was also negatively affected by clothianidin (during 3 of 4 weeks), imidacloprid (2 of 4) and thiamethoxam (1 of 4). 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 experiments using these taxa provide reliable assessments of the threats of neonicotinoids to the most vulnerable freshwater species.