In search of evidence for the experience of pain in honeybees: A self-administration study

Abstract

Despite their common use as model organisms in scientific experiments, pain and suffering in insects remains controversial and poorly understood. Here we explore potential pain experience in honeybees (Apis mellifera) by testing the self-administration of an analgesic drug. Foragers were subjected to two different types of injuries: (i) a clip that applied continuous pressure to one leg and (ii) amputation of one tarsus. The bees were given a choice between two feeders, one offering pure sucrose solution, the other sucrose solution plus morphine. We found that sustained pinching had no effect on the amount of morphine consumed, and hence is unlikely to be experienced as painful. The amputated bees did not shift their relative preference towards the analgesic either, but consumed more morphine and more solution in total compared to intact controls. While our data do not provide evidence for the self-administration of morphine in response to pain, they suggest that injured bees increase their overall food intake, presumably to meet the increased energy requirements for an immune response caused by wounding. We conclude that further experiments are required to gain insights into potential pain-like states in honeybees and other insects.

Behavioral and neurophysiological evidence suggests affective pain experience in octopus

“…Reversal of pain-associated spontaneous and cognitive behaviors by analgesics is considered to be strong evidence for the presence of pain. Among invertebrates, the use of analgesics to demonstrate potential pain experience has had mixed results ( Barr et al., 2008 ; Barr and Elwood, 2011 ; Groening et al., 2017 ; Puri and Faulkes, 2010 ). Analgesia-induced place preference in mammals is widely accepted to signal pain experience; however, a common criticism of such studies is that the chosen analgesic drug is innately rewarding, and its hedonic quality is sufficient to create place preference even in animals in neutral affective states ( Sufka, 1994 ; Tzschentke, 2007 ).…”

Assessing negative and positive evidence for animal pain

“…Self-administration of analgesics provides a compelling case for pain experience (Colpaert et al 1980), but there are problems with this approach in crustaceans, not least because it is not clear what might be an effective analgesic should the animals experience pain. I am not aware of any attempts with crustaceans, but one attempt with honey bees given the opportunity to ingest morphine did not find that their preference for morphine increased when they were injured (Groening et al 2017). This might be because a) bees do not experience pain; b) they do feel pain but ingested morphine does not act as an analgesic; or c) they do feel pain, and morphine acts as an analgesic but the association was not formed because the bees could sample morphine and non-morphine solutions within the time that it took for morphine to act.…”

Ethical considerations for invertebrates

“…They also demonstrate subjective experience, evidenced by individual differences in learning ability (Dyer et al 2019;Howard et al 2019a). Thus, they achieve some of the criteria set out by M&P but may fail at other important criteria such as the experience of pain (Groening et al 2017), which has not been conclusively proven or disproven. We therefore need to consider what allows an invertebrate to be given ethical consideration.…”