Seasonal availability and sensitivity of two field-collected mayflies for the development of a standardized toxicity test

Although insects occur in nearly all freshwater ecosystems, few sensitive insect models exist for use in determining the toxicity of contaminants. The objectives of the present study were to adapt previously developed culturing and toxicity testing methods for the mayfly Neocloeon triangulifer (Ephemeroptera: Baetidae), and to further develop a method for chronic toxicity tests spanning organism ages of less than 24 h post hatch to adult emergence, using a laboratory cultured diatom diet. The authors conducted 96-h fed acute tests and full-life chronic toxicity tests with sodium chloride, sodium nitrate, and sodium sulfate. The authors generated 96-h median lethal concentrations (LC50s) of 1062 mg Cl/L (mean of 3 tests), 179 mg N-NO3 /L, and 1227 mg SO4 /L. Acute to chronic ratios ranged from 2.1 to 6.4 for chloride, 2.5 to 5.1 for nitrate, and 2.3 to 8.5 for sulfate. The endpoints related to survival and development time were consistently the most sensitive in the tests. The chronic values generated for chloride were in the same range as those generated by others using natural foods. Furthermore, our weight-versus-fecundity plots were similar to those previously published using the food culturing method on which the present authors' method was based, indicating good potential for standardization. The authors believe that the continued use of this sensitive mayfly species in laboratory studies will help to close the gap in understanding between standard laboratory toxicity test results and field-based observations of community impairment.

Section: Discussionmentioning

confidence: 99%

“…Nominal chloride concentrations for the treatments were as follows: 37 mg Cl -/L (control), 70 mg Cl -/L, 112 mg Cl -/L, 196 mg Cl -/L, 364 mg Cl -/L, and 700 mg Cl -/L. Nominal N-NO 3 concentrations were as follows: 0 mg N-NO 3 /L, and 1300 mg SO 4 2-/L. Test conditions are summarized in Table 2.…”

Section: Chronic Toxicity Testing Proceduresmentioning

confidence: 99%

Full‐life chronic toxicity of sodium salts to the mayflyNeocloeon trianguliferin tests with laboratory cultured food

Soucek

Dickinson

2015

“…The need therefore exists to develop additional model organisms that may be more representative of native fauna and whose use could better elucidate the underlying mechanisms of ion sensitivity. Although several toxicology studies have used field‐collected Ephemeroptera, Plecoptera, and Trichoptera taxa e.g., and have evaluated that approach as a standardized method , such studies can be hampered by lack of organism availability at certain times of year and by variability in organism sensitivity . The parthenogenetic mayfly Neocloeon triangulifer (formerly Centroptilum triangulifer ) has been reared successfully in a stream‐side laboratory and used in subsequent toxicity testing .…”

Section: Introductionmentioning

confidence: 99%

Elevated major ion concentrations inhibit larval mayfly growth and development

Johnson

Weaver²,

Nietch

et al. 2014

Anthropogenic disturbances, including those from developing energy resources, can alter stream chemistry significantly by elevating total dissolved solids. Field studies have indicated that mayflies (Order Ephemeroptera) are particularly sensitive to high total dissolved solids. In the present study, the authors measured 20-d growth and survivorship of larval Neocloeon triangulifer exposed to a gradient of brine salt (mixed NaCl and CaCl2 ) concentrations. Daily growth rates were reduced significantly in all salt concentrations above the control (363 µS cm(-1) ) and larvae in treatments with specific conductance >812 µS cm(-1) were in comparatively earlier developmental stages (instars) at the end of the experiment. Survivorship declined significantly when specific conductance was >1513 µS cm(-1) and the calculated 20-d 50% lethal concentration was 2866 µS cm(-1) . The present study's results provide strong experimental evidence that elevated ion concentrations similar to those observed in developing energy resources, such as oil and gas drilling or coal mining, can adversely affect sensitive aquatic insect species.

“…In their study of the effects of imidacloprid on insects in a stream mesocosm, Mohr et al observed a significant decline in numbers of Ephemeroptera, stocked in late May, starting 50 to 60 d later (i.e., from late July onward). Echols et al , assessing the suitability of 2 mayfly species for whole effluent testing, also reported reduced availability of 2 bivoltine native North American mayfly species, in June and July.…”

Section: Discussionmentioning

confidence: 99%

Response of the mayfly (Cloeon dipterum) to chronic exposure to thiamethoxam in outdoor mesocosms

Pickford

Finnegan

Baxter³

et al. 2018

Thiamethoxam is a widely used neonicotinoid insecticide that has been detected in surface water monitoring programs in North America and Europe. This has led to questions about its toxicity to nontarget insects, specifically those with an aquatic life stage. To address the uncertainty associated with possible impacts from environmental exposures, a chronic (35-d) outdoor mesocosm study with a formulated product containing thiamethoxam was conducted. The specific focus of the study was the response of mayflies (Ephemeroptera), which have been reported to be particularly sensitive in laboratory studies. A range of concentrations (nominally 0.1, 0.3, 1.0, 3.0, and 10.0 mg/L thiamethoxam), plus untreated controls were tested, and the abundance and emergence of mayflies (Cloeon dipterum) were assessed weekly for 35 d. Mean measured time-weighted average exposures were within 6% of nominal over the duration of the study, with the mean half-life of thiamethoxam in each treatment ranging from 7 to 13 d. Statistically significant reductions in both larval abundance and adult emergence were observed at 10.0, 3.0, and 1.0 mg/L following 1, 2, and 3 wk of exposure, respectively. Exposure to 0.1 and 0.3 mg/L thiamethoxam had no statistically significant effect on larval mayfly abundance or adult emergence at any point in the study. These findings support a 35-d no-observed-effect concentration (NOEC) of 0.3 mg thiamethoxam/L for mayflies (C. dipterum) under chronic conditions. Furthermore, because the 95th percentile of environmental concentrations has been reported to be 0.054 mg/L, these results indicate that populations of C. dipterum and similarly sensitive aquatic insects are unlikely to be significantly impacted by thiamethoxam exposure in natural systems represented by the conditions in our study.