By Richard Levine
I recently visited the USDA Beltsville Agricultural Research Center (BARC) in Maryland to check out their Electron & Confocal Microscopy Unit, a state-of-the-art facility which allows researchers to obtain incredible photos of really tiny specimens, including insects, mites, nematodes, fungi, and viruses.
The director, Dr. Gary Bauchan, is a specialist in microscopy, and he was there that day with Dr. Ronald Ochoa, a research entomologist who specializes in mites. Readers of this blog might remember their names from last February, when a graduate student at The Ohio State University named Samuel Bolton enlisted their help in photographing a new mite species he had found on campus called Osperalycus tenerphagus, also known as the Buckeye dragon mite.
Dr. Ochoa is completely fascinated with mites, and for good reason. For one thing, they’ve been around for a really long time — mite fossils that are 410 million years old have been found at the Rhynie cherts in Scotland, and recently mites that are 230 million years old have been found in amber. Next, they are incredibly diverse. Depending on the species, mites can be predators, herbivores, parasites, parasitoids, fungivores, etc. Some are host-specific, meaning they only feed on certain plants or animals, while others are generalists and will feed on multiple hosts.
While some are relatively large — ticks, for example — most are very small and difficult to see with the naked eye, so we’re not really sure how many species even exist. They can be found practically anywhere on the planet, even in Antarctica, the deep ocean, or on your face (Demodex folliculorum or Demodex brevis). In fact, Dr. Ochoa reckons that the number of mite species is probably pretty close to the number of insect species.
“If you could grab the Hubble Space Telescope looking out into space and instead move it to look towards the Amazon and see what is going on between the trees of the rainforest, I am sure you would see a universe of different mites gliding in the air,” Dr. Ochoa said recently to a reporter from the Smithsonian Institution. “You and I cannot see them, but they are there, floating from one canopy to another canopy, all waiting to be discovered.”
Dr. Ochoa and Dr. Bauchan were joined that day by three scientists from South America who traveled all the way to Maryland so Gary could take photos of mite samples they had brought with them. Javier Huanca Maldonado, from the Universidad Nacional Agraria La Molina in Peru, brought spider mites in the family Tetranychidae, which are agricultural pests. The other two scientists from Brazil’s São Paulo State University, José Marcos Rezende and Marcel Santos de Araújo, brought white mites (Tarsonemidae) and some primitive cave mites (Opilioacaridae) to be studied and photographed.
“There is a huge diversity of these mites that are still to be discovered,” Rezende said. “We know so much about the birds of Brazil, about Brazil’s mammals, its reptiles, its insects … but mites? Who knows?”
The equipment in the lab is impressive. The low-temperature scanning electron microscope (LT-SEM) can magnify tiny creatures by 120,000 times. Samples must be photographed in a vacuum, so in order to avoid damaging soft tissues — ones that contain liquids — they are first frozen in liquid nitrogen and then coated in platinum in order to protect them. Then the photos are taken at -130°C.
The LT-SEM is especially good for photos of mites because their exoskeletons are generally softer than those of insects, which means they can be more prone to damage in a vaccum. In addition, the LT-SEM can record clear images of a mite’s integument — a fancy word for its skin — which is covered by waxy microplates.
Until about ten years ago, the existence of these microplates hadn’t even been discovered. But now, thanks to LT-SEM, we know that in some mite families the integument of each species is different from all of the others, which allows scientists to “fingerprint” the different species.
Besides the LT-SEM, the lab is equipped with other microscopes that can be used for various purposes. The variable pressure scanning electron microscope, for example, can be used for larger, hardier specimens that do not need to be frozen and coated in platinum. The confocal laser scanning microscope can be used to observe fluorescent specimens in 3D, and the digital light microscope provides videos and 3D-like images of large specimens at high resolution.
In the following video, Dr. Bauchan demonstrates the equipment:
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Richard Levine is Communications Program Manager at the Entomological Society of America and editor of the Entomology Today Blog.