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Bio-control jewel

PU Antony, July 23, 2013
the big fight The wasp injects an  intoxicating venom to paralyse the cockroach. photo by author

Meet nature’s femme fatale, the Jewel Wasp. A bio-control agent against cockroaches, she needs no male to reproduce. Intoxicating her prey before feeding its live tissues to her young ones, P U Antony finds her one fascinating species

A very important aspect of parental care in animals is to provide the best possible diet to the offspring. Here is a precocious insect which assures a continuous supply of live tissues of its kill to her young ones until they are old enough to hunt for live prey themselves.


The Jewel Wasp, also known as the “Emerald Cockroach Wasp “is known to be a bio-control agent against cockroach in some parts of the world. She typically lives for several months and can be found in various tropical regions of Africa, India, and the Pacific Islands.

The Wasp is a parasitoid, which means that she is a killer of her prey. A parasitoid is different from a parasite in that the latter does not kill its victim. It lives off its victim until it moves on to a new host or dies. The parasitoid, on the other hand, intends to kill its victim.

The wasp injects various mind controlling toxins into a cockroach’s brain and then leads it to her burrow where her hatched larva ultimately slowly eats the live cockroach from the inside out. The wasp starts by stinging the cockroach around its midsection. This temporarily paralyses the cockroach’s front legs.

When the cockroach’s ability to move is slightly inhibited, the wasp makes a much more precise sting, injecting her venom into the part of the cockroach’s brain that controls its ability to initiate walking. The venom injected into a specific part of the brain of the cockroach doesn’t actually affect its general motor skills. The venom seems to inhibit the cockroach’s desire to flee from potential danger and even pain, specifically by inhibiting its ability to begin complex behaviours, such as walking.

The venom does this by blocking a specific neurotransmitter called “octopamine”. Once they are coerced into moving, they can walk just fine, though they have trouble forcing their body to continue to move. The wasp acts like a microscopic neurosurgeon who delivers the right dosage of venom every time. If too little venom is administered, the cockroach will escape; and if too much is given it will kill her host. The host needs to remain alive in order to provide her young ones with the right nourishment.

Once the wasp has injected her venom into the right part of the cockroach’s brain, she easily leads the cockroach back to her burrow by gently pulling on the antennae. This pull provides enough external stimuli to coax the sedated cockroach to walk, so long as the wasp continues to tug and guide it. Once in the burrow, the magic happens. The wasp lays an egg on the cockroach’s abdomen. She then exits the burrow and blocks the hole. The cockroach then leads a reclusive life in the burrow. After three days, a little larva is hatched and proceeds to feed on the delectable cockroach.

 The larva doesn’t actually eat the entire cockroach right away. Instead, the baby wasp chews into its abdomen and proceeds to live there as a parasite. Over the next week, the larva eats the cockroach’s internal organs in such an order that the cockroach will stay alive for quite some time (four or five days). Once the larva has eaten all the internal organs of the cockroach and the cockroach dies, it then forms a cocoon inside the cockroach’s body from which a full grown female wasp eventually emerges.

The Emerald Jewel Wasp has only one target, and that is the American Cockroach common in south Indian households. She is the check that nature put in place, to keep the American Cockroach population under control. The precision which she exhibits when she immobilises her prey is honed over thousands of years of adaptation. To help explain this let us look at how this wasp breeds.

She does not mate. She simply lays an egg on her host and from that egg a female is born, never a male. There is no need for a male wasp to fertilise the egg. The reason for this is that her daughter is her clone. It is herself reborn with all of the knowledge that the mother had. So what we really see with these and many other wasps is a genetic copy of the mother. This is why there is no male. Breeding with a male would change the daughter and put the offspring at a significant disadvantage.

Humans receive 50 per cent of their genes from the father’s sperm and 50 per cent of their genes from the mother's egg. This is why we are not identical to our parents, or our siblings. The Jewel Wasp, on the other hand, evolved by trial and error as a product of natural selection. Those Jewel Wasp best suited to hunt the American Cockroach survived to reproduce. Those that did not adapt to this died, leaving behind a population of Jewel Wasps that could easily immobilise a prey 10 times bigger than their own size.

This is the very reason why there is no male involved in the reproduction cycle. Mixing male genes into the reproductive cycle would make for an weaker offspring. The ability to be precise comes directly from the mother, and she passes that precision on to her daughters.

A recent study using radioactive labeling proved that the wasp stings precisely into specific ganglia. When researchers removed the part of the cockroach’s brain that the wasp normally stings (the sub-esophageal ganglia), which boost the signals that cause the cockroach to walk, the wasp went on stinging the cockroach for as much as 3 minutes in various spots, trying to find the sub-esophageal ganglia.

Normally, it takes the wasps only around 15 seconds to locate and sting the correct spot. Researchers have actually successfully created an antidote for the Jewel Wasp’s venom, which allows the cockroach to exhibit more normal behaviour after being stung. Further, they have also found that if other areas of the cockroach’s brain are injected with the Jewel wasp’s venom, even those around the sub-esophageal ganglia, there seems to be no major effect on the cockroach.


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