Wasp Larvae Practice Food Safety

From refrigeration and pasteurization to hand washing and health inspections, humans go to great lengths to prevent foodborne illnesses—and it turns out we're not alone. A new study reveals that the parasitic emerald cockroach wasp (Ampulex compressa) has developed its own food hygiene technique, cleansing its cockroach victim using a cocktail of antimicrobial liquids.

(Read a related article on food safety in National Geographic magazine.)

When reproducing, emerald cockroach wasp mothers attach one egg to the leg of an American cockroach (Periplaneta americana). Once the egg hatches, the larva bores a hole in the insect and moves inside. There, it feeds on the roach's internal organs before spinning a cocoon within the carcass and eventually emerging as an adult wasp. (Watch a related video on the parasitic black wasp.)

However, due to the cockroach's unsanitary living conditions, many bacteria, viruses, and fungi also make their home on the cockroach, infecting the young wasp's only food source and threatening its survival.

"It was clear that a species that feeds on these cockroaches had to protect its food and ... itself from foodborne illnesses," said Gudrun Herzner, an entomologist at the Institute of Zoology at the University of Regensburg in Germany and lead author on the study. "This [environment] was a good place to look for antimicrobial defense mechanisms." (Related: "Cockroach Brains May Hold New Antibiotics?")

A Potent Combination

Herzner and her team wanted to investigate just how these wasp larvae were protecting themselves from the microbes in their contaminated food source. So the team began collecting droplets of a liquid secreted by the larvae when inhabiting their hosts.

Analysis revealed that the two most prevalent chemicals in the secretion—mullein and micromolide—in combination were effective antimicrobial agents against bacteria commonly found on American cockroaches.

Though both compounds had been previously identified in other organisms, Herzner's study, published this week in the Proceedings of the National Academy of Sciences, was the first to find this specific combination of chemicals in the same source. "It seems that it's exactly this mixture [that gives] broad-spectrum protection from different kinds of bacteria," Herzner said.

This broad-spectrum strategy also prevents the development of bacterial resistance, similar to combination antibiotic therapy in humans. "[The wasps] virtually soak their cockroaches with these antimicrobial secretions, and in this way, they sanitize the cockroach," said Herzner.

An Ugly World

Parasitization, such as what the emerald cockroach wasp does to cockroaches, is very common in the insect world, said Jim Whitfield, professor of entomology at the University of Illinois, who was not involved with the study. "Almost every species of insect larva has some kind of parasite that attacks it ... It's a pretty ugly world out there if you're an insect larva," he said.

However, this wasp larva's specific method of defense is quite unique, Whitfield added.  "Normally the adult female wasp produces the compounds that protect the offspring, and not the larva itself. In this case, it sounds like it's the larva that produces it," he said.

The discovery of this antimicrobial combination could one day even be used in food safety techniques or antibiotic therapies for humans. In fact micromolide has been a promising lead compound against the microbe that causes tuberculosis, Herzner said.

She added that there could be other compounds, more potent and powerful than what the wasp larvae employ, out there right now. "Evolution might still be working to make an even better combination [for defense]," Herzner said. (Related: "Drug-Resistant Bacteria Found in 4-Million-Year-Old Cave.")