SETAC Spotlight: The impact of environmental factors on the growth and development of a lab culture of Cloeon dipterum

CEA presented 1 platform and 9 posters at SETAC Seville in May 2024. We will be showcasing each of these presentations in a series of ‘SETAC Spotlight’ articles. This week is the last SETAC Spotlight.

SETAC Spotlight: The impact of environmental factors on the growth and development of a lab culture of Cloeon dipterum

Authors: Katie Smith¹, Hanna Schuster¹, Nadine Taylor¹,

¹Cambridge Environmental Assessments, RSK ADAS, Boxworth, UK

Non-standard test species are used in the refinement of aquatic risk assessments of plant protection products (PPPs) in the European Union. EPT taxa (Ephemeroptera, Plecoptera and Trichoptera) are of particular interest as they are classed as sensitive and vulnerable to PPPs, however, they are difficult to work with in a laboratory setting and the seasonality of their life cycle restricts the frequency and scale of ecotoxicity testing.

The mayfly, Cloeon dipterum, is a highly abundant species across the UK and Europe, with larval stages residing in ponds and river margins. Yet little is known about how laboratory conditions affect survival and sub-lethal endpoints such as emergence and larval growth, physiology and morphology, resulting in challenges for a standardised testing approach. In the natural environment there are many confounding factors contributing to growth and development, adults emerge across varied time periods and the emergence success rate and survival of larvae are largely unknown.

To improve of our understanding of these influences, wild-caught C. dipterum larvae were used in non-standard, bench-scale, laboratory tests. The larvae were subjected to different variations (from a perceived optimal to stressed conditions) of environmental conditions, i.e., modifying temperature, photoperiod and food provision. They were monitored from early instars (L1 and L2) at the beginning of the test, until emergence. Data was collected for body length, instar stage, food intake, molting, time to emergence and survival.

C. dipterum showed distinct trends in response to different conditions. In particular, sub-optimal temperature and food availability resulted in a significant impact on development and survival. High temperatures resulted in a faster rate of development, while at low temperatures development was found to be slower. Mortality increased with both low (16˚C) and high (22 and 24˚C) temperatures and occurred between Day 12 and 23. At lower food provision levels, mortality was recorded between Day 12 and 37. This increased mortality was mainly observed at instars L5 – L7 for all stress conditions. No clear trend was found for different photoperiods.

At optimum conditions (20˚C and higher food provision), there was a larger range of body length and instar stages, which indicated the natural variability of the individual development compared to the stress conditions.

These results will be help, to progress the reliability of mayfly testing in a regulatory context and inform future effect modelling.