Is it time for insect researchers to consider their subjects’ welfare?

Box 1. Eight criteria for assessing evidence relevant to pain in animals 

1. Nociceptors. The animal possesses receptors sensitive to noxious stimuli (nociceptors).
2. Integrative brain regions. The animal possesses integrative brain regions capable of integrating information from different sensory sources.
3. Integrated nociception. The animal possesses neural pathways connecting the nociceptors to the integrative brain regions.
4. Analgesia. The animal’s behavioral response to a noxious stimulus is modulated by chemical compounds affecting the nervous system in either or both of the following ways:

   1. The animal possesses an endogenous neurotransmitter system that modulates (in a way consistent with the experience of pain, distress, or harm) their responses to threatened or actual noxious stimuli.
   2. Putative local anesthetics, analgesics (such as opioids), anxiolytics, or antidepressants modify an animal’s responses to threatened or actually noxious stimuli in a way consistent with the hypothesis that these compounds attenuate the experience of pain, distress, or harm.
5. Motivational trade-offs. The animal shows motivational trade-offs, in which the disvalue of a noxious or threatening stimulus is weighed (traded-off) against the value of an opportunity for reward, leading to flexible decision-making. Enough flexibility must be shown to indicate centralized, integrative processing of information involving an evaluative common currency.
6. Flexible self-protection. The animal shows flexible self-protective behavior (e.g., wound tending, guarding, grooming, rubbing) of a type likely to involve representing the bodily location of a noxious stimulus.
7. Associative learning. The animal shows forms of associative learning in which noxious stimuli become associated with neutral stimuli, or in which novel ways of avoiding noxious stimuli are learned through reinforcement. These forms of associative learning go beyond classical conditioning in which a single conditioned stimulus overlaps temporally with an unconditioned stimulus.
8. Analgesia preference. The animal shows that they value a putative analgesic or anesthetic when injured in one or more of the following ways:

   1. The animal learns to self-administer putative analgesics or anesthetics when injured.
   2. The animal learns to prefer, when injured, a location at which analgesics or anesthetics can be accessed.
   3. The animal prioritizes obtaining these compounds over other needs (such as food) when injured.