Minute Creatures Raise Mighty Concerns
Becker, Hank, The World and I
Allowing scientists to study mites in unprecedented detail, an exciting new technology reveals information useful for fighting species that are pests and employing others as biological control agents.
Ronald Ochoa, the U.S. Department of Agriculture's expert on mites, is about to transform the 200-year-old study of mites--a science called acarology. Ochoa is a research associate at the Systematic Entomology Laboratory (SEL) of the Agricultural Research Service (ARS) in Beltsville, Maryland. He specializes in the systematics of mites--that is, the discovery, scientific description, classification, and naming of agriculturally important mite species.
"Mites have attacked the world's vertebrates, invertebrates, and plants for millions of years," he says. "Although they remain a constant threat to economically important crops, stored grains, livestock, wildlife, and humans, only about 10 percent have been described or named."
Ochoa is also curator of mites for the National Collection of Insects and Mites, housed at SEL and belonging to the Smithsonian Institution's National Museum of Natural History in Washington, D.C. Recently, he teamed up with cytologist William Wergin and botanist Eric Erbe, both of ARS' Beltsville Agricultural Research Center Nematology Laboratory, to study mites with a sophisticated new technology called low- temperature scanning electron microscopy (LT-SEM).
Mites come in a variety of body shapes and normally have four pairs of legs. "But because of their small size--some no bigger than the point of a needle (80 micrometers in diameter)--mites are difficult to study biologically," Ochoa explains. "Their intricate structures and the distribution of their hairs, called setae, are important for identifying them, but their minute size can be a problem."
Lack of detailed, accurate information about the identity, biology, and ecology of mites often has serious consequences for U.S. agriculture. "More than 6,000 mite species infest nearly every plant important to agriculture," notes Ochoa. "In the United States, they cause annual economic losses estimated in the billions of dollars from decreased food, fiber, and ornamental [plant] production. Invasive mite species are among the primary culprits."
Increased world trade will continue to distribute mite infestations widely. "Once they've become established in a new area, certain biological characteristics allow mite populations to escalate rapidly to pest status," Ochoa observes. "High egg production, various modes of reproduction, short life cycles, many dispersal techniques, and adaptability to diverse environmental and ecological conditions all contribute to their success."
Magnifying the minuscule
Wergin, who developed LT-SEM technology, explains how it works: "Unlike conventional microscopes, a SEM apparatus does not use light passed through a glass lens to magnify images of a specimen. Rather, the images are formed and magnified by electrons passing through a magnetic field that functions as a lens. The images can be displayed and recorded on a cathode-ray tube similar to one in a television."
According to Ochoa, "LT-SEM was used to obtain--for the first time ever--highly magnified, clear images that show the details of intact mites and how they interact with and attack plant and insect hosts." He adds that LT-SEM technology provides a powerful new tool that can benefit not only the systematics of mites but research on other microorganisms as well.
To prepare (or fix) a mite specimen for viewing, Ochoa and Erbe use liquid nitrogen, which is at -320*F. This cryofixation instantly freezes the mite in its natural state on the host and prevents it from moving or becoming distorted.
"Although conventional SEMs have been used by acarologists for the past 30 years, Wergin's technique has many advantages," says Ochoa. "We can magnify mites more than 50,000 times. …