Scoping Review (2019 to 2024) Suggests Significant Variation in, and Poor Reporting of, Anesthesia Practices in Model Insects

Although insect researchers are not legally mandated to follow the 3Rs, the precautionary use of pain reduction methods like anesthesia may be an important research refinement, especially given increasing evidence that pain is plausible in some insects. This review aimed to determine if and how insect researchers working with ten model species use anesthetics in the lab. We searched four databases for publications on each model species that contained a mention of anesthesia, with the agent named, from 2019-2024. Then, we confirmed whether anesthesia was used for putative pain reduction or loss of consciousness purposes in a laboratory setting. Papers that met these criteria were found for five species: the western honey bee, migratory locust, house cricket, black soldier fly, and fruit fly. Cold was reported as an anesthetic method for all five species. Isoflurane, sevoflurane, carbon dioxide, desflurane, halothane, flyNap (triethylamine), dyclonine, etomidate, ketamine, 2,6-diisopropyl phenol, propofol, tricaine mesylate, chloroform, xenon, eugenol, alcohol, ether, and nitrogen gas were also reported (mostly, in fruit flies). The majority of studies did not report exposure procedure, anesthetic dose or exposure time; when reported, these details varied widely, suggesting a lack of standardization in anesthesia protocols. Further, 24.2% of anesthetic-records used cold, an anesthesia method not recommended by veterinarians for invasive procedures in insects. Overall, our review suggests standardized, species-specific anesthesia protocols could improve scientific reproducibility and refine insect experimentation.