European Corn Borer, Ostrinia nubilalis, and Its Microsporidian Pathogen, Nosema pyrausta

Editor's note: We strongly believe that changes in attitude are necessary to promote changes in pest management practices, such as the broader adoption of biological control. By teaching school children about biological control, hopefully they will be in a better position to make informed decisions as adults. This article was written by 17 fourth graders at Leal School, Urbana, Illinois, who conducted their biological control experiment with the help of Dr. Lee Solter, University of Illinois.

The European corn borer (ECB) was brought to the United States from Europe (that's pretty obvious) in 1917. ECB were first found in Massachusetts, later spreading to Illinois, Minnesota, Iowa, South Dakota, Nebraska, Kansas, Missouri, Indiana, and Ohio.

It costs farmers 1.1 billion dollars because of the damage European corn borers do to corn crops. ECB damages over 5% of the corn in a field. This damage is caused by the ECB eating through the vessels of the cornstalk, which keeps the nutrients from flowing from the ground to the leaves. Eventually, the plant loses its nutrients and may die. Besides corn, the ECB also eats peppers, cotton, potatoes, and many other vegetables.

Pesticides can be used to control ECB, but pesticides can kill other insects that are harmless, such as ladybugs and spiders, that may even help farmers. So scientists are experimenting with microsporidia, a one-celled protozoan that infects the ECB and sickens it. The disease or microsporidia that we used in our experiment to infect the European corn borer is called Nosema pyrausta.

Lee Solter came to our classroom to talk to us about the ECB, and the experiment we were going to do with microsporidia. We wanted to see if the microsporidia would spread from infected ECB larvae to uninfected ECB larvae in cups of insect diet and on corn leaves. We did research in books in our classroom and we searched the Internet, then we each wrote a hypothesis about what we thought would happen with the experiment. Sixteen students predicted that the microsporidia would spread from the infected larvae to at least one uninfected larva; one predicted that the microsporidia would not spread to any of the uninfected larvae.

We went in two different groups to the University of Illinois entomology laboratory to perform the experiment. First, we had a tour of the lab. Lee told us about a hood that scientists use to protect themselves from any harmful fumes or insect scales, a refrigerator that would not burn if the entomology lab caught on fire, and an electron microscope that takes an hour to start up. We saw liquid nitrogen tanks where they preserve microsporidia and insects. The liquid nitrogen is -196 degrees C. We also saw a water purifier, an emergency shower that is used in case of a chemical spill, and a growth chamber. Inside the growth chamber there are lots of different kinds of larvae. Because of all the insect food, the growth chamber had a nose-plugging stench.

After the tour, we started our experiments. Each person used forceps to put 3 uninfected ECB larvae in a diet cup. Then we put 3 larvae infected with N. pyrausta in the diet cup, placed a lid on the cup, and wrote our name on the lid. Next, each person put 5 uninfected larvae and 5 infected larvae on the top part of a corn plant which was in a 250-ml flask of water. Cotton was stuffed around the cornstalk to keep the ECB larvae from climbing down into the water. We put a netting called a sleeve over the corn plant and tied the sleeve tightly around the neck of the flask. We wrote our names and the date on a piece of blue tape on each flask. We put the corn plants and the diet cups in the growth chamber.

After a few weeks of wondering what would happen in our experiment, Lee sent us the results by e-mail and we recorded our individual results on a classroom chart. To find out how many larvae were infected and how many were uninfected, Lee dissected the European corn borers in the diet cups and looked at them under the microscope. If she found microsporidia, the larva was infected. If she didn't see microsporidia, the larva was not infected. Then Lee cut the cornstalks in half. If there were any European corn borers inside the cornstalk, she dissected them as well.

In the diet cups, there was some transmission of the microsporidia from the infected larvae to the uninfected larvae. We knew transmission took place because there were more than three infected ECBs in almost every diet cup. The most infected larvae in one cup was 6; two people recorded those results. Three people recorded the lowest number of infected larvae, which was 3. Seven people recorded 4 infected larvae and five people recorded 5 infected. For our group of 17 students, the average number of infected ECB larvae was approximately 4.35. Some of the ECB died and disintegrated in the diet cup. We think that the ones that died early were probably the infected larvae.

Our experiment in the diet cups was a success because the microsporidia transferred to over half of the uninfected European corn borers. On the cornstalks, some of the ECB tunneled through the cotton and drowned, some chewed through the sleeves and escaped. At the end of the experiment on the cornstalks, there were not enough European corn borers left to determine if transmission occurred.

If we were to try the experiments with European corn borers and N. pyrausta again, these are some things we might do differently:
Try using larger diet cups so the ECB might not eat through the lid of the cup during their wandering stage. We know that some of the ECB escaped from the diet cups during the wandering stage before they pupated because Lee found some European corn borers pupating somewhere in the growth chamber and some on the floor of the lab.
To prevent the ECB from boring through the cotton and cornstalk in the flask of water, we could try a more natural environment like in a greenhouse or in a simulation of a cornfield.
To keep the ECB from boring into the water and drowning, we might try using wax, clay, plastic, or a sponge around the cornstalk in the neck of the flask.
Put netting around the bottom of the corn plant and then stick the plant in a pot of dirt.
Try to make the water smell like something unpleasant for the ECB, perhaps even one of their predators.

The Authors:

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