Photographs of a female
broad mite (Polyphagotarsonemus)
latus on the surface of a
pepper leaf. The photo
was taken with a low-temperature
scanning electron microscope.
The specimen was held on a
new, high-angle, azimuth
rotation specimen holder and
frozen in its natural position
with liquid nitrogen. These
five photographs can be
copied, cut, and folded to
create a box photo that depicts
the mite's three-dimensional
Not really insects, mites are more closely related to ticks and spiders
and come in a variety of body shapes and sizes. Some are no bigger than
the point of a needle. Yet they are a constant threat to economically
important crops and stored grains, as well as to livestock, wildlife,
The miteor any other species of insect and nematodecan
now be viewed more extensively by low-temperature scanning electron
microscopy (LTSEM) when placed in a new holder designed by Agricultural
Research Service botanist Eric Erbe.
Standard specimen holders for LTSEM viewing can cost several hundred
dollars each. The expense can sometimes curb experiments that require
several holders. Holders are also limited by the tilt capabilities of
the microscope's stage, which makes it difficult for researchers to
see all sides of a specimen once it is placed into the microscope.
Erbe's inexpensive specimen holder, made of scrap metal, allows a 90-degree
tilt for observation of the edges of flat specimens. It can also be
used to obtain side, front, and back views of specimens normally mounted
with just the top side exposed. Rotating samples in this new holder
between each observation and recording yields a series of micrographs
that provides a 360-degree view of an object or specimen.
In the field, scientists, extension agents, and farmers typically collect
samples onto a copper-plate specimen holderor even onto a penny
if that's all that's availableand then contact freeze the specimen
to keep it in optimal condition. To do this, they use a portable cryo-work
chamber filled with liquid nitrogen, which freezes samples in milliseconds.
Then they place the samples in a dry shipper, cooled to 321°F,
and send them to ARS scientists in the Electron Microcopy Unit at Beltsville,
Maryland, for examination.
There, scientists place the frozen specimens in Erbe's special holders
for observation under the LTSEM at up to 50,000x magnification.
"The specially built holder is an important accessory for scientists
interested in obtaining more complete descriptions of many small pests,"
says Erbe. "Accurate identifications will help prevent the annual
economic losses they cause, estimated to be in the billions of dollars."
Erbe has developed a unique display of insects and mites by turning
these micrographs into what he calls box photos. A single photographed
layout of the top and sides of a mite, insect, or nematode can be copied,
cut, and folded to form a cube that displays the creature in three dimensions.
You can design your own box photo by checking out our Science for Kids
web site at http://www.ars.usda.gov/is/kids/weirdscience/story7/buildamite.htm.By
formerly with ARS.
This research is part of Plant Diseases, an ARS National Program
(#303) described on the World Wide Web at http://nps.ars.usda.gov.
Eric Erbe is with the
Genomics Improvement Laboratory, Bldg. 177B, 10300 Baltimore Ave.,
Beltsville, MD 20705; phone (301) 504-8046, fax (301) 504-8923.