Have you ever thought what it might be like to not be in control of your own body?  Most people will never have to worry about such a terrifying event but for the prey of the fiendishly manipulative Jewel Wasp this is an everyday concern.  The mature Jewel wasp does not paralyse or kill its cockroach prey — that would be too kind a gesture.   Instead this parasitoid wasp stings its prey not once but twice ultimately removing any free will from the insect so that it can be used as a live food supply for both the wasp and its offspring.  The wasp first stings the cockroach in the abdomen causing front leg paralysis.  Once the insect is partially paralysed the wasp then initiates a more diabolical sting to the wasp’s brain leaving them unable to move.  After the second sting has been successfully delivered the wasp leaves its prey for 30-40 minutes before returning.

During this initial 30 minute period the cockroach vigorously grooms itself going through all the regular grooming behaviours that a non-stung wasp would display.  After the initial 30 minutes the cockroach becomes lethargic displaying a complete lack of ability to initiate or maintain walking or escape behaviours for the next 3-7 days.  The wasp returns once the lethargic process has taken over the cockroach’s free will.   The wasp can then take the cockroach by its antenna and lead it back to its nest to be used as a live food source.  If the wasp is particularly hungry at the time it may cut of the top of the cockroach’s antenna and proceed to extract hemolymph directly from the cockroach on route back to its nest.  Researchers were curious as to whether the Jewel Wasp actively searches the brain of its prey to find the specific center associated with walking behaviour?

Laboratory experimentation suggests that the Jewel Wasp does actively search the brain of its prey until it locates the SEG region (associated with walking).  To prove this theory three different groups of cockroaches where used.  The first group had their SEG regions completely removed via a surgical procedure, the second group had the connective tissues connecting the thorax and the SEG severed but nothing was physically removed from the animal, and the third group was what is known as a group of sham-operated cockroaches.  These animals were given lesions to appear as though they underwent surgery but in fact no surgery took place.  This would tell us if wasps had a preference to sting or not sting cockroaches with previous scares.   The results are difficult to refute, wasps spent more than five times as much time inside the heads of cockroaches without a SEG region than they did in those with severed connective tissues or sham-operated specimens.  This demonstrates that the wasp is in fact actively searching for the SEG region of the cockroach’s brain.  Is the sting alone enough to cause these behavioural changes in the cockroach?

The cause of these behaviour changes is not the sting alone but the injection of venom from the wasp into the SEG of the cockroach.  Scientists tested this theory by injecting venom into the SEG and other areas of the cockroach brain.  The walking drive of cockroaches was only affected when the wasp venom was injected directly into the SEG region of the brain.  This tells us that the wasp must sting and inject its venom into that precise area in order for behavioural changes to be seen in the cockroach prey.  So, next time you see an insect acting strangely you may wonder is that insect acting of its own free will or has its mind been hijacked by some sinister predator?

Source: Gal, R., Libersat, F., 2010.  A Wasp Manipulates Neuronal Activity in the Sub-Esophageal Ganglion to Decrease the Drive for Walking in its Cockroach Prey.  PLoS ONE 5(4): e10019.