Electron Microscopy and Pest Control
Posted November 5, 1998
By Kathleen Gregg Ph.D
Many scientists today wrestle with the challenge of researching biological controls for insect, and weed, and disease causing pests. One method to control pests that
destroy crops or plants is to introduce natural predators that will eat the pests. In determining which predators will be the most effective for a specific pest, one factor a biologist
might study is how the predator attacks and eats its prey. In many cases of these type of pests, both predator and prey are quite small. Studying details in the table manners of a predator
this size is best accomplished with an electron microscope. During the preparation of a specimen for the electron microscope, however, the predators usualy either drop their prey or
vomit on it, thus ruining the specimen for it's intended viewing purpose. Finding a method to sneak up on a predator and kill it before it realizes what is happening was quite a task
and took some special techniques developed by German photographer Volker Steger.
Steger used one particular specimen preparation technique with the seven-spotted ladybug, Coccinella septempunctata. Adult ladybugs, kept in a petri dish, are
not fed to make sure they will be very hungry when their prey, in this case a species of aphid, is introduced. The hungry ladybugs are quick to catch the aphids with two of their legs
and to start eating. Steger then rushes the petri dish to the freezer. As the temperature drops, the ladybug eats more and more slowly until finally, it stops. The petri dish is removed
from the freezer before the ladybug is dead, and so that ice crystals will not form and destroy it. Ether is then used to slowly kill the ladybug. After the ladybug has died, it is exposed
to alcohol that coagulates its' proteins so that it keeps a tight grip on its prey. They are immersed in plastic and coated with a fine layer of gold, a good conductor of electricity.
They are then ready for the electron microscope.
Steger's electron microscope photographs have been very useful for scientists. Discovering where and how an insect attacks a prey organism can indicate the efficiency
it may have as a biological pest control organism. Steger also feels that the act of using natural predators to destroy pests can be extremely helpful in a person's own garden.
Activity
Compare and contrast the use of insects as a natural biological control and the use of pesticides as a chemical control. Use the addresses given below to obtain
current documents that can be used as sources for your research. Compile the data into a report. At the completion of the report, include your views on the two methods.
To read more, see the article "Dining on the Fly", written by Josie Glausiusz in the February 1998 issue of Discover or go to their web site to search for the article
in their archive. http://www.discover.com/archive/index/html
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