It’s arguably one of the more terrifying things to happen as a researcher. Imagine all your research colonies suddenly dying due to a mysterious cause.

Not only were these cockroaches dying, but they were dying in perhaps one of the most gruesome ways possible. American cockroaches are well-known for their quick movements and reactions to stimuli like wind, light, touch, and more. However, these cockroaches first exhibited slow, sluggish movements, while holding their wings out like they were about to take flight. Then, the cockroaches were eventually decapitated, with their heads found completely separated from their bodies.

The researchers isolated a few of the sick roaches into cups, and they waited for their culprit to emerge. A few yellow-black larvae appeared and were quickly followed by yellow pupae. Eventually, adults emerged from the pupal case, and moved in a unique manner.

They confirmed the identification of the suspect using a Scanning Electron Microscope (SEM). Using these photographs, they were able to determine that the suspected parasitoid was none other than Megaselia scalaris, which is a well-known member of the scuttle flies. Scuttle flies are part of the family Phoridae, which contains over 4000 species. Scuttle flies get their common name from the adult’s unique way of “scuttling” around, rather than taking flight. These flies are more commonly known for infesting anything rotting, be it plant material, carcasses, and more gross things. In the pest management sphere, these flies are commonly known for infesting unclean drainpipes, sewers, and more. They are also commonly known as “coffin flies” for their penchant for infesting carcasses.

 

 

However, a few species of this group are known to parasitize other arthropods and are also known to decapitate their hosts when they are done with them. Yet, this was the first time that scuttle flies were documented parasitizing American cockroaches, as previous documentation only described this group parasitizing ants and bees.

So, are we in for a brand new method of managing American cockroaches? Hard to say at this juncture. But, we at least now have documentation that Megaselia scalaris, a scuttle fly, can parasitize American cockroaches in such a way that does lead to their demise. As we well know, American cockroaches can harbor some of the highest percentages of pathogens that cockroaches can carry. Therefore, any kind of tool that we could potentially have against these pests could be a boon. However, further research is necessary to determine if M. scalaris could potentially become a problem following the death of the cockroaches. After all, we don’t want to create a new problem while we’re trying to solve one!

While this biocontrol agent may be a bit of a pipe dream at the moment, at the very least, this study provides a starting point, albeit a slightly morbid one. For example, by examining the biochemistry of how M. scalaris can “take over” its host, we may be able to find a novel biocontrol agent that can specifically target the nervous system of American cockroaches, and lead to their demise. So, while we solved the hijinks in this murder mystery of these American cockroaches, there’s still mysteries to be solved down the line.

Article by Laura Rosenwald, BCE

References

Arafat, E.A., El-Samad, L.M. & Hassan, M.A. Scuttle fly Megaselia scalaris (Loew) (Diptera: Phoridae) endoparasitoid as a novel biocontrol agent against adult American cockroaches (Periplaneta americana). Sci Rep 14, 9762 (2024). https://doi.org/10.1038/s41598-024-59547-w

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