Insects Feel Pain Just Like Us, New Study Says

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As the world population will reach 10 billion by 2050, the United Nations has recommended mass production of insects for food. But ethical values ​​and the defense of the animal cause have never been so present in the news. Consumption and thought patterns are changing in the face of discoveries concerning animal pain. Recently, British and Iranian scientists demonstrated that the fly is very likely able to feel pain via a certain biological mechanism, nociception, present in mammals. The finding rekindles the heated debate about protecting animal welfare, which should now include insects, say the study scientists.

Nociception—the ability to sense pain—is essential to an organism’s survival and general well-being. It corresponds to all of the body’s functions allowing it to detect, perceive and react to potentially harmful internal and external stimuli. This goes through the nociceptive receptors, located on the nerve endings, giving the alert and provoking a nervous message of “pain” when they “spot” an actual or possible attack.

Pain is a negative subjective experience, generated by the brain. Nociception and/or pain can be inhibited or facilitated by what are called descending neurons in the brain or “descending pain controls”, a real adaptive advantage. Indeed, for example during a fight, an injured animal will not feel pain immediately (the receptors are inhibited). But once the fight is over, top-down pain controls can facilitate nociceptive processing, so the animal will seek to protect its wound while it heals.

This is why, today, vertebrate studies go before ethics committees to prove that the value of the research outweighs any harm to the subjects. Cephalopods such as octopus and squid are beginning to benefit from the same protection. But this is not the case with insects, since the question of whether they have such top-down control, or the neural circuits allowing it, has rarely been explored.

Recently, researchers from Queen Mary University in London and Tehran in Iran, compiled the available literature on pain in insects, including behavioral, molecular and anatomical studies. Their unexpected findings of pain perception similar to humans are published in the journal Proceedings of the Royal Society B: Biological Sciences.

Modulation of nociception

You must first know that indeed, nociception can be accompanied by the sensation of pain, but this is not always the case. Previous research has shown that animals and insects possess physiological systems that respond to what in animals would be described as a painful experience. But it is very difficult to judge whether an insect feels pain, because this negative experience is strongly controlled by the brain.

According to the authors, behavioral work shows that insects can modulate behavior after stimulation of nociceptive receptors, both by their peripheral and central nervous systems. In other words, some insects visibly act “normally” after injury, continuing to feed or not changing their behavior. This evidence was used, first, in the scientific literature, to indicate the absence of pain in insects.

However, the authors note that it is ” more likely to demonstrate insect prioritization of other behavioral needs », in fact reducing the nervous message of pain in certain contexts. For example, a cricket that is eaten by a praying mantis continues to eat, or a fly, one of whose legs is amputated, acts in a normal way in the face of a palatable stimulus. Such modulation is at least partly controlled by the central nervous system since the information mediating it is processed by the brain. It is the same process that in humans, faced with certain emergency situations such as an accident, inhibits the pain resulting from an injury. The latter does not manifest itself immediately, in particular thanks to adrenaline. Once “safe”, the pain appears.

Central nervous system control of nociception is further supported by neuroanatomical and neurobiological evidence. Indeed, the researchers explain: Anatomically, insects have descending neuronal projections from the brain to the ventral nerve cord, where nociceptive behavior is performed “.

The defensive strike reaction and the nervous system of the tobacco hornworm (the larva of the tobacco hornworm Manduca sexta). © M. Gibbons et al., 2022

Finally, molecular studies reveal the pathways involved in inhibiting this behavior. Even though insects lack animal opioid receptors, other neuropeptides, such as drosulfakinin, allatostatin-C and leukokinin, could be possible modulators of nociception in them.

Taken together, these data seem to indicate that insects possess some kind of pain response control system, similar to ours.

The research team says in a statement: We argue that insects most likely have central nervous control over nociception, based on behavioral, molecular, and anatomical neuroscientific evidence. Such control is consistent with the existence of an experience of pain “.

Well-being of insects and intensive production

In a 2021 report, the UN explains: Edible insects can diversify diets, improve livelihoods, contribute to food and nutrition security and have a smaller ecological footprint than other protein sources “.

In the context of an ever-increasing world population and conventional farming, which is a major contributor to climate change, the massive production of insects for food would therefore seem to be the best alternative. But the ethical implications have not been taken into account, as animal welfare protections do not currently cover insects.

Future research should therefore aim to better characterize the modulation of nociceptive behavior, and determine whether this is associated with pain in insects. These studies will help clarify whether we should afford ethical protection to insects in potentially harmful contexts, such as agriculture and research, as is beginning to be the case with octopuses. However, earlier this year, scientists called for the closure of the world’s first octopus farm, fearing for the welfare of farmed animals. That hasn’t stopped Spanish multinational Nueva Pescanova from announcing that it will start marketing by 2023.

The authors conclude: Furthermore, elucidation of the neural and molecular pathways of top-down control of nociception in insects may lead to the use of insects as a model organism for human pain states involving top-down control dysfunction. “. Insects, considered pests or parasites, are much closer to us. This study will make us think twice before using an insecticide or crushing a spider. Being at the top of the food chain does not give us the right to mistreat the other links for our appetite alone, under cover of the ecological argument.

Source: Proceedings of the Royal Society B: Biological Sciences

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