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

Julia Groening,Mandyam V Srinivasan,Dustin Venini

doi:10.1038/srep45825

Julia Groening, Mandyam V Srinivasan + Show 1 more

Open Access

https://doi.org/10.1038/srep45825

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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.

Highlights

Which animal taxa have evolved the capacity to experience pain is an ongoing debate
Cephalopods have recently been added to the list[12] due to their complex behaviour and learning ability, which is comparable with lower vertebrates
It has been demonstrated in praying mantis[28], crickets[29] and honeybees[30] that morphine injection reduces their defensive response to a noxious stimulus in a dose-dependent way and that this analgesic effect can be blocked by naloxone

Summary

Introduction

Which animal taxa have evolved the capacity to experience pain is an ongoing debate. Pain is defined as ‘an aversive sensation or feeling associated with actual or potential tissue damage’[1]. The presence of opiate receptors and response to analgesics in presumably painful conditions can be a useful indicator of pain experience in animals[27] It has been demonstrated in praying mantis[28], crickets[29] and honeybees[30] that morphine injection reduces their defensive response to a noxious stimulus in a dose-dependent way and that this analgesic effect can be blocked by naloxone. These studies suggest that insects have opiate binding sites or opioid general sensitivity similar to vertebrates[4,31] or, alternatively, non-opioid receptors to which morphine binds[32]. Two different types of injuries were tested: (i) a continuous pinch to the hind leg, and (ii) amputation of part of one middle leg

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