Motivational trade-offs in a cockroach: impact of conditions, injury, and development

The ability to flexibly trade off access between competing or antagonistic stimuli (motivational trade-offs) is a key criterion for assessing whether animals can feel pain. However, in some commonly farmed, exterminated, and studied insect orders such as Blattodea (cockroaches and termites), the ability to make motivational trade-offs is unconfirmed, which makes it difficult to assess their welfare needs. Here we gave cockroaches a choice between access to shelter or nutrition across a series of linked experiments to assess how motivational trade-offs are flexibly adjusted due to external conditions and injury and develop across ontogeny. We found cockroaches would adjust how willing they were to access nutrition instead of shelter based on the intensity of the light they would be exposed to and how long they had been deprived of food. They can therefore make flexible motivational trade-offs. We also found that injury reduces willingness to accept light exposure when accessing nutrition, which is consistent with the idea of the sensation of pain reducing risk-taking behaviour. Finally, we showed that juvenile cockroaches can make motivational trade-offs, but only towards the end of their development, and that young juveniles do not trade-off. All together our results provide comprehensive evidence that cockroaches can make highly flexible motivational trade-offs, filling in a gap in our understanding of cognitive abilities in insects linked to their ability to feel pain. These findings indicate the need to design legislation, housing, and production methods that account for and enhance invertebrate welfare.