Nerve research: eating the cake and keeping it alive - a parasitic wasp dictates the behavior of its prey by injecting venom straight into its brain. A fascinating glimpse into the connection between biochemical processes in the brain and behavior
Yael Laban, Ben Gurion University of the Negev
Ampulex compressa on a stamp from Malaysia
Every mother tries to provide her children with fresh and clean food, and the wasp Ampulex compressa, whose larva feeds on cockroaches, is no exception. But the parasitic wasp, which lives in tropical areas, does not have a refrigerator and must keep its food fresh in another way. At the same time, she must make sure that the food stays in its place from the moment the egg is laid until the end of the meal and the embodiment of the larva. How does a wasp cause an American cockroach, three times its size, to follow it to its burrow and wait "patiently" - while still alive - for 8-7 days until the wasp larva finishes eating it? The answer is amazing: the wasp is able to dictate to the beetle a series of certain behaviors it desires by injecting venom directly into its brain.
"This is the only case known to us in nature of a direct injection of venom into the central nervous system," says Prof. Frederic Libersat, a researcher in the Department of Life Sciences and the Zalotovsky Center for Nerve Research at Ben Gurion University. Neuroscientists use the cockroach as a laboratory animal, just as other scientists use mice. The patchy nervous system is relatively simple, but it is similar in many respects - structurally and functionally - to the nervous system of vertebrates, including humans. The wasp ampholex compressa provides researchers with an opportunity for fascinating research.
The use of venom to change behavior is rare in nature. There are many venomous predators, but most use venom to kill or paralyze their prey, in order to eat it immediately. "In such cases," explains Libersat, "paralysis of the prey also paralyzes the respiratory muscles and blood vessels, and the prey dies quickly." On the other hand, the wasp has to keep the cockroach alive and fresh, but prevent it from escaping during the week that the larva feeds on it." To achieve this, the wasp inserts its stinger into the cockroach's head and the venom is injected directly into the brain. Libersat and his group marked the wasp's venom with a radioactive substance that allows its location to be discovered after the sting. In a microscopic examination of the stinging cockroaches, you can see that the venom is concentrated in a certain area of the brain. In another study, receptors were found at the tip of the stinger with the help of which, apparently, the wasp senses or "tastes" the brain and makes sure that the sting is done in the right place. The result of the bite is surprising: the cockroach opens in thirty minutes of intensive self-cleaning, after which it turns into a kind of "zombie".
Self-cleaning (grooming) is a common action in animals, the purpose of which is to get rid of dirt, parasites, fungi and the like. Even in insects it is a complex behavior that includes, among other things, cleaning the head and abdomen with the front legs and cleaning the legs and tentacles with the mouth. How does the venom injection trigger this? A chemical analysis found that wasp venom contains dopamine, a neurotransmitter that is also active in the human brain and is related to the mechanisms responsible, among other things, for movement and motivation. It was found that artificially injecting dopamine into the cockroach's brain causes it to self-clean, and if the cockroach is injected with a substance that contradicts the action of dopamine (dopamine antagonist) before the wasp sting, the self-cleaning decreases significantly. From this it seems that the presence of dopamine in the venom causes the cockroach to clean itself with such vigor.
What benefit does the wasp derive from self-cleaning? One of the hypotheses put forward by Prof. Libersat is that this way the caterpillar will eat food as clean as possible from fungi and other parasites, just as we wash our hands before eating.
After the meal has finished cleaning itself, the wasp grabs the cockroach's tentacle and pulls the captive after it into the burrow it prepared ahead of time. The cockroach is not paralyzed: it walks on its feet, its muscles are not damaged and in experiments it was found that it is also able to fly and swim. And yet he does not resist and does not run away! Libersat explains: "The leg muscles are reflexively controlled by local ganglia, which are the cockroach's equivalent system to the spinal cord of vertebrates. On the other hand, as in humans, it is the brain that decides when to walk, where to turn and which legs to move. The wasp takes over the control mechanism of the brain in the nervous system."
The wasp leads the cockroach like a dog on a leash into the burrow, and lays one egg on it. Then she closes the burrow with dry leaves and leaves. In another study, Libersat's research group found that cockroaches stung by a wasp survived without water and food better than cockroaches that were not stung or injected with a paralyzing toxin derived from another venomous wasp. It turns out that the wasp sting also affects the captive's metabolism and oxygen consumption, with the aim of keeping it "fresh" for a longer time.
The larva hatches from the egg two days after laying, pierces a hole in the cockroach's body and feeds on the hemolymph (the "blood" liquid in insects) for three more days. Then the larva penetrates the cockroach's body, eats its internal organs (thus finally killing it) and incarnates inside it. After three weeks, a mature wasp emerges from the cocoon, ready to look for a new victim.
Libersat's research is basic research, but it may have applied implications. The inability to control movement and produce voluntary movements also characterizes some diseases in humans, such as Parkinson's disease. It is interesting to note that in Parkinson's patients there is a dramatic change in the amounts of dopamine in the brain. A better understanding of the processes in the brain of the stung cockroach may advance research in this area. Changes in the amount of dopamine in the brain or its absorption capacity are also characteristic of various mental disorders - depression, schizophrenia, drug addiction and more. The wasp venom Ampolex Compressa may help in finding pharmacological tools that will affect the dopamine system.
In a completely different field, six-legged insects, and especially the cockroach, serve as an excellent model for building mobile robots because they have an amazing ability to walk in varied terrain conditions. The engineers must learn how to control the movement of six legs, coordinating them and adapting to the surface. Experience gained over millions of years of evolution will be at their disposal, if they know how to get to it.
