Ampulex compressa (the emerald cockroach wasp) relies almost completely on the American cockroach (Periplaneta americana) for both a food source and reproduction. The emerald cockroach is a solitary wasp (like the wasp species Sceliphron caementarium) and along with all other adult wasps, is unable to eat firm food but rather relies on sucking or drinking the hemolymph of the American cockroach and other insects that differ based on their differing locations (Bartlett 2004).  

However, wasps are not only predators but prey as well. Some common predators of wasps include dragonflies (such as Somatochlora hineana), a very large variety of birds that vary by the location of the wasp but include tree swallows (Tachycineta bicolor), red-winged blackbirds (Agelaius phoeniceus), frogs such as the American bullfrog (Rana catesbeiana) and even other wasps.

Interactions with the American Cockroach

The emerald cockroach wasp has one of the most advanced known methods for disabling and utilizing its host. Although it is not uncommon for parasites to use their host for reproduction, the emerald cockroach wasp has a tactic that is unlike any other organisms’: a venomous sting directly to the brain that completely deteriorates the cockroach’s desire to escape. However, the cockroach isn’t paralyzed, without sensation, or dead but rather fully alive with motor functions intact. Only the cockroaches desire to escape from the wasp is changed.

What exactly happens to the cockroaches ganglia is still a mystery. The state of a stung cockroach known as “hypokinesia” is bizarre in that while the cockroach will not voluntarily move, it will still regain its upward position if flipped on its back, groom itself when it is aggravated by a stimulus and even swim when placed in water. Banks, et al. conducted an experiment to test if this strange behavior exhibited by a stung cockroach is due to a lessening of biogenic amines in the cockroach’s central nervous system.  The test compared control cockroaches, cockroaches stung by Ampulex compressa and cockroaches with decreased amines (induced by reserpine, a sedative compound). The varied cockroaches were placed into an arena where their physical activity was measured by how many times they crossed quadrants over a 10 minute time period. As expected, the control cockroach population had the highest level of activity, crossing quadrants an average of 11.2 and 15.5 times in two separate tests. However, the reserpinized and stung cockroaches both remained in their exact location with only a few slight turns on their axis for the extent of the 10 minutes (Banks, et al. 2012). Unfortunately, although both the reserpinized and stung cockroaches behaved similarly in this test, when amine levels were evaluated in the both the head and subesophageal ganglia it was found that the stung cockroach population had a normal or even slightly higher than average amine level than the control. The reserpinized cockroaches had miniscule amounts of amines as expected, proving that a reduced level of amines is not the cause for the hypokinesia state in stung cockroaches. Other experiments have attempted to determine how exactly the strange venom of the emerald cockroach wasp works, but its true method can still only be hypothysized. Ampulex compressa is truly amazing and unique in its techniques for immobilizing its host, making it an incredibly successful parasitoid.

Graph 1


More about the experiments relating to the emerald cockroach wasps venom can be found through at Toxicon and Current Biology as well as A Wasp with a Taste for Brain.

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