locust plague

Swarms of locusts have arrived in Israel from Egypt and farmers are on alert for fear of damage to agricultural produce. Let's find out what can turn a solitary and harmless grasshopper into a destructive band

By: Zvi Atzmon

A prosperous field soon turns into an oil field after the chewing visit of a group of locusts
A prosperous field soon turns into an oil field after the chewing visit of a group of locusts
Photo: A. S. A. P. Creative Schankz, Shutterstock

There are substances that have "luck in life" - they are famous for playing key roles in living things. This is, for example, the "universal fuel" of life processes, the ATP; So is the ring AMP - cAMP - acting as an intracellular "secondary messenger" in extremely diverse processes.

Serotonin, which is a common intercellular messenger in many processes in different animals, also plays a key role and publication accordingly. It recently became clear that serotonin is a key factor in the creation of locust swarms, which cause enormous damage to agriculture.

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Influence on feelings and behavior

Serotonin, which is a derivative of the amino acid tryptophan and is also known as 5-HT 5 (hydroxy-tryptamine), is involved in peripheral processes in our body, such as the narrowing of blood vessels after an injury (hence its name, serotonin: the tone caused by the serum, the blood fluid) due to the contraction of the smooth muscles in their walls. This is the first action of serotonin that was identified, about 60 years ago; The main store of serotonin used in this process is in the platelets.

However, most of the serotonin in our body is secreted by special cells in the intestinal wall. Quantitatively, only a small amount of all the serotonin in the body works in the central nervous system, in the brain, but the range of brain-behavioral processes in which it is involved is extremely broad.

Among the behaviors and brain functions in which serotonin is involved, and the deficiencies resulting from its abnormal activity or its receptors, one can name mood and depression; sleep; Appetite; body temperature regulation; learning and memory; aggression; obsessive-compulsive disorder (OCD); Hallucinations and more. No wonder that nerve fibers (axons) that secrete serotonin are spread over large areas of the brain, although their origin is much more focused - mainly from the raphe nuclei in the brainstem.

The serotonin molecule
The serotonin molecule

The effect of serotonin

Nerve cells, whose nerve messenger (neurotransmitter) is serotonin (serotonergic cells), secrete serotonin that binds to specific serotonin receptors that protrude from the membranes of nerve cells affected by serotonin. Several types, and their subtypes, of serotonin receptors have been identified in different brain areas - a minority of them are direct receptors (receptors that act as ion channels), while the majority are metabotropic receptors (that affect ion channels through secondary messengers). The wide variety of different serotonin receptors explains, among other things, the many effects of serotonin on behaviors, feelings and functions.

Many substances from an external source have an effect on the amount of serotonin or on serotonin receptors; These are psychoactive substances that affect feelings and behavior. These substances include drugs, hallucinogens ("hallucinogens") and other psychoactive substances. Among the drugs, we can mention the reuptake inhibitors (from the synaptic gap to the secreting serotonergic cell) of serotonin - SSRI's (such as Prozac and Seroxat); Among the hallucinogens - psilocin (a hallucinogen derived from a fungus), mescaline (derived from cacti such as peyote) and LSD; The substance MDMA, known as ecstasy, increases the amount of serotonin in the synaptic space and induces feelings of closeness and hallucinations.

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The plague of Egypt

But our concern here is not the effects of serotonin on man, but on one of his greatest enemies - the grasshopper, and referring to its band form, swarms of locusts. In the January 2009 issue of the weekly Science, Anstey and his colleagues from the Department of Zoology at the University of Oxford, the Department of Zoology at the University of Cambridge, and the Department of Biology at the University of Sydney, report on experiments showing that an increase in the level of serotonin is a necessary and sufficient condition for turning a solitary grasshopper, averse to society and harmless, into an individual in a flock Wreaking havoc.

Around 8000 species of grasshoppers are known in the world, of which only about 12 species form migratory swarms when the amount of food is reduced. A large swarm of the desert locust (Schistocerca gregaria) - the species studied by Anasti and his colleagues, can include billions of individuals; In its search for plant food, such a migrating swarm may travel dozens of kilometers a day. A prosperous field soon turns into an oil field after the gnawing visit of a flock of locusts, one of the ten plagues of Egypt.

The differences in color (the color of the details changes completely, darkens), in the body structure (the muscles become stronger) and in the behavior between the solitary desert grasshopper and the banded grasshopper are so prominent that they were considered separate species of insects, and only in 1921 it became clear that this is one biological species with two external appearances (phenotypes) Various.
Many locusts follow the food

Anstey and his colleagues knew that it was possible to turn a solitary desert grasshopper into a flock by tactile stimuli on its hind limbs (which under natural conditions means "crowded here") or by sight and smell stimuli of grasshoppers. When these stimuli continue, the grasshopper "decides" that it needs to be flexible, abandon the policy of peaceful isolation and join a swarming flock. The researchers asked themselves whether touch stimuli in the hind limbs and the sight of grasshoppers and their smell, would increase the level of serotonin in the grasshopper's body. It turned out that the answer is positive, and in banded grasshoppers the level of serotonin is about three times higher than solitary grasshoppers.

Furthermore, if the grasshoppers were treated with a substance that inhibits serotonin activity (serotonin antagonist), despite the appropriate stimuli, the grasshoppers did not become bandy. The complementary experiments were also crowned with success: artificially adding serotonin turned solitary grasshoppers into gregarious ones even when there were no natural gregarious stimuli.

It seems to me that it is possible that the transformation of single and isolated grasshoppers into flocks of grasshoppers can serve as a beautiful demonstration of the transformation of negative feedback into positive feedback: as long as the grasshoppers are spread out in an environment rich in food, the grasshopper does not see other grasshoppers or smell them, and certainly other grasshoppers He is not touched - and he is disgusted by such sights, smells and contacts. However, when food sources dwindle, despite the strong aversion to companionship, the grasshoppers gather at the few food sites that are still left, and each grasshopper is exposed - reluctantly - to the presence of other grasshoppers.

When the amount of stimuli increases beyond a certain threshold value, serotonin is secreted, and it activates a positive feedback mechanism: the grasshopper becomes herd in nature and longs for company, which increases the flow of stimuli, which therefore encourages the flow of serotonin in its body and its desire for the company of grasshoppers and God forbid.

* Now on the way to food: a guide to cooking locusts