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Mighty Mites Ubiquitous,
Inconspicuous, Harmful, Helpful
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Mites have successfully colonized nearly every
known habitat on Earth. They thrive in polar and alpine extremes, tropical
lowlands, and desert barrens, surface and mineral soils to depths of 32 feet,
cold and hot surface springs, and subterranean waters with temperatures as high
as 50°C. They live in freshwater streams, ponds, lakes, and
seawater—even at ocean depths of 15,000 feet.
Mites are among the oldest of all terrestrial animals, with fossils known from
the early Devonian period—nearly 400 million years ago.
Mites are also incredibly diverse, second only to insects in the number of
species known to live on Earth. Yet the 48,200 species described by scientists
may make up only 10 percent of the total number of mite species that exist; the
remaining 90 percent has yet to be studied.
Research on mites, as on many other arthropods, is hampered by their minute
size. Most species are too small to be seen without a microscope. Some are only
about as large as a good-sized bacterium. Indeed, the human follicle mite is so
small it can raise an entire mite family on one human hair follicle. And honey
bee tracheal mites live and breed within a bee's tiny respiratory tubes.
But some mites are easily seen. For example, red velvet mites, which can be up
to 0.4 inches long—among the giants of the Acari—can be seen hunting
on the ground or on tree trunks. And although water mites are rarely more than
a few millimeters long, their bright colors and rapid movement often bring them
to our attention. Unfortunately, these larger species are but a small fraction
of the total.
In this issue of Agricultural Research,
ARS researchers discuss new technologies
that apply computerization and digital imaging to help cope with these problems
of size. Through flash-freezing of specimens and use of a low-temperature
scanning electron microscope, scientists have obtained images of mites caught
in the act of feeding. This nondestructive technique also allows detailed
examination of tiny structures such as mouthparts and hairs, or setae. These
methods are shedding invaluable light for the first time on how mites sense and
interact with their environment.
This knowledge is important because mites can be both destructive and
beneficial. For example, many species cause serious damage to plants by feeding
on them or transmitting diseases. Mites also affect people and animals by
causing allergies, spreading diseases, acting as parasites on their bodies, and
contaminating dried food products.
At the same time, many groups of mites are our best hope for controlling other
mite pests. These tiny predators feed voraciously on other mites and control
their populations naturally.
Agricultural Research Service scientists have a long and distinguished history
of providing research and service on mites. Since the late 1800s, ARS'
Systematic Entomology Laboratory (SEL), in Beltsville, Maryland, and its
predecessors have been home to several well-known mite researchers, including
E.W. Baker, renowned as one of the fathers of modern acarology.
Today, SEL researchers apply new technologies to help solve problems caused by
mites. The laboratory also helps maintain and improve the National Collection
of Insects and Mites in conjunction with the Smithsonian Institution in
Washington, D.C. This unique and priceless collection of over 30 million
specimens took nearly 120 years to assemble. It is absolutely critical to our
ability to understand mite diversity and relationships, make predictions about
possible new pests, and archive records of past efforts.
The mite systematists in SEL and other ARS researchers have focused on mite
species that have invaded the United States from other countries. Of the more
than 1,900 species of plant-feeding mites now known to exist in the United
States, scientists believe that as many as 200 species have invaded this
country from other parts of the world. Escaping the predators, parasites, and
diseases of their native lands, these invaders run rampant in this country.
Accurate identification, classification, and information on their distribution
are absolutely vital to controlling these emergent pests.
Armed with new technologies, acarologists are finding a whole host of new
characters that will trigger some profound changes in how we view mites and how
we understand their relationships—harmful or helpful—with their plant
and animal hosts. These advances herald a new age for acarology and provide
easier, faster, and more efficient ways to control and use mites to benefit
humans.
Michael E. Schauff
Entomologist
Systematic Entomology Laboratory
Beltsville, Maryland |
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"Forum" was published in the
October 2000
issue of Agricultural Research magazine.
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