On parasites and motivation - on the wasp and the cockroach

A study conducted at Ben Gurion University explained why the cockroaches in which the wasps lay their eggs do not resist the wasp * It seems that the wasp's venom has a targeted effect on the urge to start walking and persist in it

The parasitic wasp Ampullex compressa has an interesting way of obtaining food for its offspring - the cockroach (Periplaneta americana). The wasp produces venom consisting of a mixture of different compounds and neurotransmitters that uniquely affect the nervous activity in the cockroach and thereby cause a behavioral change, and this in just two stings.

First the wasp stings its victim in the chest and causes a temporary and brief paralysis of his two front legs. She then stings him with another sting in the head and injects venom into the brain area and the SEG (subesophageal ganglion). As a result, the cockroach stops pollinating, instead it begins a typical cleaning behavior that lasts about 20 minutes, at the end of which it becomes a kind of "zombie". At this point the wasp grabs him with its tentacle and leads him, without resistance, to its burrow. There she lays eggs on it, and when they hatch, the live cockroach serves as food for the larvae for several days until their development is complete. All this without him trying to initiate a move or run away.

Why doesn't the cockroach run away? In a study conducted at Ben Gurion University Prof. Frederic Libersat from the Institute of Neurobiology in Marseille, France and Ram Gal from the Department of Life Sciences and the Zalotovsky Center for Neuroscience at Ben Gurion University tried to understand whether the cockroach's immobility is due to a decrease in its state of alertness, an increase in the stimulus threshold to start the movement or from a change in the ability to persist in walking.

Following the bite, the cockroaches do not lose the ability to move. When placed on their backs they successfully straightened up on their feet. Cockroaches that were placed in a container with water, under the risk of drowning, began to swim similarly to those that were not stung (albeit for shorter periods of time). Since the movement in swimming is very similar to walking, it seems that cockroaches do not lose the ability to use their legs. In addition, electrophysiological measurements showed that the neural activity in the leg muscles during their movement is similar to the control.

In order to check whether there is a change in the threshold of stimulation required to make the cockroach move, the researchers used a special chamber that allows an electric shock to be delivered through the insect's legs and measured the minimum voltage that causes the cockroach to move away from the place. They found that following the bite, the cockroaches escape from the electrifying environment only at voltages up to 3 times higher than the control, mainly in the first hours after the bite. Also, the stinging cockroaches reacted less to touch.

From this it appears that the wasp venom has a targeted effect on the urge to start walking and persist in it. The effect of wasp venom on the cockroach can be used as a model for cases where there is a separation between the neural areas responsible for initiating movement and areas responsible for the persistence and creation of movement patterns. Additionally, it can advance our understanding of how a unique composition of toxins or neurotransmitters modulate certain behaviors or responses. For example, even in humans, in certain cases of deep depression or brain damage following an injury or a stroke, it is seen that there is not always an impairment in the ability to activate the muscles, yet there is no self-initiated movement. It seems that there is still much to learn from the insects about the nervous system and the effect of various compounds on behavior, and perhaps to better understand processes that also occur in the human brain.

For the scientific article in current biology