Behavioural, but not motivational, trade-offs in a cockroach

Abstract

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 (Blaptica dubia) a choice between access to shelter or to nutrition across a series of linked experiments to assess whether they are capable of motivational trade-offs and if they are flexibly adjusted due to external conditions and/or injury and develop across ontogeny. We found cockroaches avoided a food reward when it was exposed to light (a behavioural trade-off), but they did not adjust their preference flexibly in response to lighting intensity or increased hunger level (no motivational trade-off). We did find 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 match adults in not making a motivational trade-off. All together our results provide much-needed evidence for criteria of whether insects feel pain and suggest upper limits to cognitive complexity and flexibility in Blattodea. These findings can be integrated with other neurological and behavioural measures to help us judge how we treat insects and other invertebrates in our care.