In experimental research, insects have become an important component in fields as diverse as genetics, infection biology and the environment. They are often used for 'relative replacement', as they are considered to be less sensitive species. Despite not being protected by Directive 2010/63/EU on the protection of animals used for scientific purposes, recent advances raise ethical questions: should we re-evaluate our practices regarding the use of insects?
Animal consciousness: generalizing with caution
The term “consciousness” in defined as the process by which an animal experiences perceptions and emotions, based on the material substrate of its nervous system (Irwin et al. 2022). Since Darwin's theory of evolution, consciousness research has been extended to various animal species. The scientific study of consciousness has experienced a resurgence in the 21st century. The phylogenetic tree of animals, reveals that consciousness emerged independently in at least three distinct clades (vertebrates, arthropods, and cephalopod mollusks) with very different neuronal architectures. According to Barron et al. 2016, insects could thus have subjective experiences analogous to those of vertebrates. In accordance with the collective expertise of the France’s National Research Institute for Agriculture, Food and the Environment (Inrae) on Animal Consciousness for the year 2017, it is necessary to ascertain whether the cognitive capacities that give rise to consciousness can result from evolutionary processes and whether these capacities could be the product of evolutionary convergences in unrelated species but faced with similar environmental constraints. In April 2024, 287 experts signed the New York Declaration, establishing an emerging consensus on the reality of consciousness in certain vertebrates and invertebrates, including insects. This position emphasizes the importance of giving a prominent place to the consideration of animal consciousness in our reflections and actions in favor of animal protection.
Animal pain and Directive 2010/63/EU
The French Commission Nationale de Protection des Animaux Utilisés à des fins Scientifiques (CNEA) defines pain as "an unpleasant sensory and emotional experience associated with or resembling that of an actual or potential tissue lesion". The 2010/63/EU Directive on the Protection of Animals Used for Scientific Purposes specifies that procedures involving animals should be designed to avoid causing pain. When pain or distress is unavoidable, it should be minimized to the greatest extent possible. In mammals, and more specifically in mice, observations such as facial expression, behavioral assessment, weight loss and nest building can help assess pain.
Pain in insects
The evidence for the existence of pain in insects is still subject to debate. In order to understand the current state of evidence for pain in these invertebrates, an in-depth review of over 300 studies on six insect orders was conducted by Gibbons et al. in 2022. The review employed eight criteria based on nociception, analgesia and behavior to assess pain:
Nociception and sensory integration (criteria 1, 2 and 3): Nociceptors in insects connect to higher brain regions, suggesting integration of nociceptive information.
Analgesia and preferences (criteria 4 and 8): Local analgesics affect insect behavior and preference in ways compatible with pain, but may also influence other aspects such as locomotion and learning.
Behavior and motivation (criteria 5, 6 and 7): Behavioral studies indicate that insects can heal specific wounds and make flexible choices based on rewarding and aversive stimuli.
Despite the lack of sufficient scientific data, the study by Gibbons et al. concludes that several orders of insects are likely to feel pain. The strongest evidence comes from adult flies (Diptera) and cockroaches (Blattodea), which are well-studied species. Signs of pain have also been observed in bees, wasps and ants (Hymenoptera), although fewer criteria have been met. Notably, no adult insects have been found to fail the criteria. However, there are gaps in the evidence, as pain-related neurobiology and behavior have not been sufficiently studied in most insects.
Insects and the 3Rs
Although insect research often overlooks pain, it is essential to consider their well-being. In an article published in June 2023, Crump et al. argue that taking these aspects into account can boost public confidence in science and encourage ethical practices. The ethical principle of the "3Rs" (replace, reduce and refine) can serve as a starting point for entomologists wishing to integrate insect welfare into their research and teaching activities. For instance, in 2024, the Insect Welfare Research Society proposed guidelines for the protection and promotion of insect welfare in research concerning sampling, housing, invasive methods, anesthesia/analgesia and euthanasia.
In conclusion, the growing recognition of animal consciousness, supported by the New York Declaration, together with research demonstrating that adult insects are likely to feel pain, underlines the importance of reflecting on future ethical considerations in our research practices using insects.