January 9, 2013
Emerald Cockroach Wasp: Master Of Neurochemistry and Microbiology
Alan McStravick for redOrbit.com — Your Universe Online
We all remember the dinner scene in the hit 1979 film ℠Alien´. Everything seemed fine, when all of a sudden an alien parasite emerged from the chest cavity of Ian Holm, introducing a new form of horror in the science fiction genre. But was it, in fact, science fiction? Right here on earth, in the insect world, this phenomenon appears to be nothing new.
Of course, the alien in the film was foreign and ugly and frightening. The perpetrator of this very same behavior in our world, on the other hand, is a fascinatingly beautiful creature. The emerald cockroach wasp, with its sparkling shades of blue and green, uses its natural beauty to hide its insidiously cruel behavior. This attractive insect is, at heart, a parasite. And its host is none other than the ancient and disease laden cockroach. But how does a parasite manage to maintain its health in the cesspool that is the cockroach?
It all starts when the female wasp identifies the host for her progeny and then lays her eggs onto the cockroach. The cockroach, typically far larger than an adult wasp, should have no problem fighting off its impending fate. And it would be able to but for one important fact: the emerald cockroach wasp apparently attained its doctorate in neurochemistry somewhere along its evolutionary journey.
Once a cockroach has been singled out for its gruesome fate by a female wasp, she delivers a surgical sting to the abdomen of the unlucky insect. This administration of toxin temporarily paralyzes the front legs of the soon-to-be home for her eggs. Once subdued, she then delivers the knockout blow into the head of the cockroach, delivering venom into the part of the roach´s brain known as the sub-esophageal ganglia. Short of actually killing the host cockroach, which would render it ineffective for its upcoming purpose, the strike actually puts the roach into a zombie-like state, rendering it less fearful and less likely to attempt an escape.
Just like when you take Fido for a walk, the emerald cockroach wasp then leads the cockroach by its antennae, willingly, to her burrow where she then lays her eggs on the leg of the cockroach. Despite the fact the cockroach is alive and, at this time, not inhibited from making a break for it for the full week to month after having been stung, the wasp´s new pet remains motionless, allowing for the larvae to mature inside it and finally eat themselves out into the world through their filthy, disease-laden incubator. A new study wanted to explore not just how the emerald cockroach wasp became adept at neural manipulation, but also how it is able to defend itself from the myriad unhealthy strains that live within this unlikely of hosts.
A team of researchers from the University of Regensburg in Germany, led by Gudrun Herzner, in the course of their study noted that the larval wasps, while incubating inside their host, secreted droplets from their mouths that were then spread around before consumption of the host would commence. Their initial hypothesis centered around the antimicrobial nature of these droplets and their suspected ability to kill off potentially deadly bacteria inside the cockroach.
As this process of droplet secretion occurs inside the abdomen of the already ℠zombified´ cockroach host, the researchers, using coverslips, were able to directly observe the wasp larvae depositing these small secretion droplets directly into the cockroaches body cavities.
"It was clear that a species that feeds on these cockroaches had to protect its food and ... itself from foodborne illnesses," according to Herzner, an entomologist at the Institute of Zoology at the University of Regensburg and lead author on the study. "This [environment] was a good place to look for antimicrobial defense mechanisms."
It should come as no surprise that we humans are not the only species on earth that have to maintain a vigilance regarding our food and its potential to spoil. The emerald cockroach wasp shares this need to preserve and protect its food supply as well. And why shouldn´t it? Inside their host cockroaches are a plethora of bacteria that, left alone, would be extremely detrimental to their larvae. One threat in particular, Serratia marcescens, is a particularly filthy Gram-negative bacteria that is found inside the body of the cockroach. Humans, when in contact with S. marcescens will often develop urinary tract infections and we can see the effects of this bacteria in moist locales within our own homes in the form of the pink stains that often line the grout of our showers and ring our toilet bowls. S.marcescens in insects is far more lethal, however.
To the larval cells, the bacteria contain several protein-degrading enzymes that work to cut them apart. If it weren´t for the secretion of the antimicrobial compounds noted above, the parasitic relationship between the emerald cockroach wasp and its host would never work out. Herzner and his team have published their findings this week in the journal Proceedings of the National Academy of Sciences.
The droplet secretions of the larvae, for the study, were added to bacterial cultures that were taken from the cockroach. The team found, rather conclusively, that these secretions were quite effective at eliminating a wide swath of bacteria, not the least of which was the mortally harmful S. marcescens. But knowing that the secretions killed the bacteria and knowing why the secretions killed the bacteria were two different questions entirely.
To learn this second and more important answer, researchers were able to isolate the secretions and submit them to study via gas chromatography-mass spectrometry in the hopes of learning what exactly the nature of the substances within the secretion was. Researchers identified nine previously unknown compounds in either of the species. Two compounds in particular were found in high percentage in the secretion. The first, called (R)-(-)-mellein and the second, micromolide, when combined were very effective in producing a broad-spectrum antimicrobial. It is interesting to note that micromolide is a natural product that scientists believe may hold the answer to treating forms of drug-resistant tuberculosis. On the other hand, (R)-(-)-mellein is known to be a natural inhibitor in the processing of certain proteins that are related to hepatitis C.
The researchers also took samples from both parasitized and non-parasitized cockroaches to see if they could locate these compounds. What they found was that the antimicrobial combination was found only in the parasitized samples. This gave a sense of confidence to the team that the presence in the parasitized host samples was a direct result of the wasp larvae, eager to sterilize their food.
“We found clear evidence that A. compressa larvae are capable of coping with antagonistic microbes inside their P. americana hosts by using a mixture of antimicrobials present in their oral secretion,” write the authors. The compounds are not new in nature. But this is the first instance that this exact combination of these two compounds has been seen in any animals, insect or otherwise.
It is this combination, believe the researchers, and its wide ranging ability to effectively sanitize the interior of its host that has helped the emerald cockroach wasp to thrive. “Food hygiene may be of vital importance, especially to the vulnerable early developmental stages of insects,” the authors claim. “The range of microbes that A. compressa larvae may encounter during their development in their hosts is unpredictable and may encompass all different kinds of microbes, such as various Gram-positive and Gram-negative bacteria, mycobacteria, viruses, yeasts and filamentous fungi. The secretion of a blend of antimicrobials with broad-spectrum activity seems to represent an essential frontline defense strategy,” they continued. Cockroaches are also known to be harbingers of such fun pathogens as Salmonella, E. coli and the eggs of various roundworms.
Along with the emerald cockroach wasp´s evolutionary doctorate in neurochemistry, it seems they are also working on a masters in microbiology. Scientists had already gleaned quite a lot of knowledge into the brain through their effective use of paralysis and zombification. Now this beautiful but insidious creature is leading the way for us into another field of science. Herzner and colleagues believe their findings will be instrumental in providing a vital new resource for the creation and production of natural products that will assist humans in fighting off disease.