Pilot trial at Sierra Streams Institute tests eugenol and TMS as humane pre‑preservation anesthesia for benthic macroinvertebrate samples
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Summary
Sierra Streams Institute piloted a field anesthesia step—using eugenol and TMS—to reduce stress in benthic macroinvertebrates prior to ethanol preservation; initial results show many taxa anesthetize rapidly and staff report reduced distress.
Sierra Streams Institute (SSI) staff presented a pilot study testing whether a short anesthesia step can reduce stress responses in benthic macroinvertebrates before preservation in ethanol.
Motivation and methods: SSI staff noted volunteer and staff concern about placing live invertebrates directly into ethanol. Drawing on published work showing reduced stress markers in some aquatic invertebrates after exposure to anesthetic agents, SSI tested two agents—eugenol (a clove‑oil derivative) and TMS/MS‑222—at field‑practical concentrations. Researchers timed exposures (15 minutes and longer in some follow‑ups), recorded movement cessation during exposure, and then moved specimens into creek water for recovery before later ethanol preservation and lab processing.
Results and observations: Both agents produced rapid anesthesia for many taxa; smaller animals anesthetized more quickly than larger ones. Some taxa (notably one large megalopteran found in a pilot test) required much higher concentrations for anesthesia. Damselflies did not survive 15‑minute immersions in the trial. Most other taxa survived the anesthetic exposure and later ethanol preservation. Field crews reported the extra step added little time and staff/ volunteer feedback was strongly positive.
“Eugenol makes me feel way better about bug collection and the preservation process,” one SSI staffer told colleagues during Q&A, and respondents noted that offering a humane anesthetic step improved volunteer willingness to participate.
Limitations and next steps: Presenters emphasized that pilot work did not include molecular or cellular stress markers; broader taxon‑specific testing, validation of effects on tissue quality for taxonomic identification, and examination of long‑term impacts on samples and DNA analyses are needed. SSI recommended that other groups consider whether non‑lethal field picks could meet monitoring goals before moving to collection and that anesthetic choices be validated for target taxa.
SSI said they will continue testing taxon‑specific responses, concentrations, and any potential effects on downstream lab analyses before recommending nationwide adoption.