How Beetle Juice Led to Virus Discovery and Solved the Mystery of Superworm Death

Scientists at Rutgers University-New Brunswick have discovered a virus that has caused a nationwide extinction of giant worms, a common food for birds, reptiles, other domestic animals and, increasingly, humans as an alternative source of protein. In doing so, they have pioneered a new way to search for and identify emerging viruses and pathogens in humans, plants and animals.

Using chopped beetle carcasses formed into a slurry and an electron microscope cooled by liquid nitrogen, the scientists report in Cell that they discovered what they called the black dieback virus Zophobas morio.

The name comes from the deadly effect of the virus on a species of mealworm, Zophobas morio, native to subtropical regions, particularly the immature larval stage of the insect when it emerges from its eggs as large brown worms. This species was named “superworm” because its larvae are larger, measuring about 5 cm long, than any other species cultivated for animal feed.

Protein-rich Z. morio larvae, a staple food for captive, often exotic, reptiles, birds, fish and amphibians around the world, mysteriously began dying in 2019, baffling pet food suppliers and pet owners.

Jason Kaelber, study author and associate research professor at the Institute for Quantitative Biomedicine (IQB) at Rutgers-New Brunswick, worked with Judit Penzes, first author of the study and a postdoctoral associate at IQB.

“Judit was trying to identify why beetle farmers were losing all their superworm colonies to a deadly disease, and I was trying to develop ways to discover new viruses that didn’t rely on DNA or RNA sequencing,” Kaelber said. “We ended up discovering the virus that swept the country and killed off the superworms.”

The scientific investigation began more than a year ago, when Penzes, a molecular virologist, was contacted by beetle farm owners whose superworms were mysteriously dying at an alarming rate. Penzes was already well-known in the industry because of previous work in which she isolated a virus that killed crickets, another popular pet food.

She began collecting giant worms from pet stores in New Jersey. “Every time I went to a pet store, I would immediately go to the feeder insect section, open the containers, and look at the worms,” she says. “They were all infected. I told the store owners what I saw that I was researching this virus and asked if I could have the container. They immediately agreed. They told me to take as many as I wanted.”

She went back to her lab, took a Magic Bullet blender, put the worm carcasses in it, and blended them at high speed. The process created a slurry of beetle juice that she took and processed using a virus purification method that separated the virus because of its density. In the final step, she shined a fluorescent light on the centrifuge tube, and the virus glowed blue.

“I said, ‘I got you,’ when I saw it,” Penzes said. “I knew then it was a virus.”

Then, Penzes worked with Kaelber, a fellow electron microscopist, to examine the virus using a cryo-electron microscope, which allows a three-dimensional view of the virus, including its interior.

“You take a virus, a protein, a cell, etc., and you freeze it so quickly that the water solidifies without turning into ice crystals,” Kaelber says. “In fact, we can determine the amino acid sequence of the protein without analyzing the DNA, and just by looking at that 3D structure, because we have very precise resolution.”

They compared the protein’s structure with all known proteins using the Protein Data Bank database hosted at Rutgers and found that it is similar to, but not identical to, a virus that affects cockroaches and is part of a family of animal viruses known as parvoviruses.

“This is something new, unlike anything that has been sequenced or imaged before,” Penzes said.

The scientists are also grateful to the country’s giant worm breeders who voluntarily sent samples once the study became known. “The breeders’ willingness to help us with our research on the virus played a huge role in getting this study published,” Penzes said.

This effort, Kaelber said, provided a “proof of concept” that cryo-electron microscopy can be used to directly discover and characterize new pathogens.

“In the future, if we have a really big outbreak, we’re going to want to use every tool we can to see what we can find,” Kaelber said. “We’d like to see diagnostic cryo-electron microscopy be routine, so that when an unknown infectious disease occurs, we have many options to identify the causative agent the same day.”

Cryoelectron microscopy has gained popularity in recent years, becoming a more widespread method for 3D analysis of known samples. However, the Rutgers work represents the first time the method has been used on an unknown pathogen.

After discovering the virus, the researchers tested a way to protect Z. morio beetles from the disease by injecting them with a closely related virus from another species that does not cause symptoms. They are now developing a vaccine based on this work.

“This finding is important for two reasons,” Kaelber said. “First, beetle farmers can use this information to protect their colonies and understand what measures will be effective or ineffective in managing the outbreak. Second, the beetle outbreak was a real-world test of the technology that we hope can be useful for rapidly investigating future outbreaks in humans, plants or animals.”

Scientists Martin Holm of the Rutgers Institute for Quantitative Biomedicine and Samantha Yost of REGENXBIO Inc. in Rockville, Maryland, also co-authored the study.