Alumni Memories

Essays on the College of Agriculture's History

Corn Borer Epidemic

By W.D. Guthrie, professor emeritus, entomology

Editor’s note: W. D. Guthrie is a professor emeritus of entomology who served Iowa State for 26 years as a faculty member, research leader of the corn borer lab and USDA-ARS collaborator. Guthrie writes about his experiences with the corn borer epidemic and the steps that were taken to build resistance.

The corn borer was first found in Everett, Mass. in 1917. The experts in those days figured that it was there since 1913 in broomcorn (a type of sorghum) from some place in Europe, I believe it was Italy, and that’s how it got established. Then it moved northward, southward and westward from there. I don’t know how far north it has gone, but my wife is from Prince Edward Island, Canada and I have seen it there. It has moved as far south as Florida, but as of 1990, the year I retired, it had not crossed the Rockies.

The corn borer doesn’t move very fast, although it can fly. It made it to Ohio sometime in the late 1920s. We do know the exact year it made it to Iowa though — 1942. John Brindley was the one to actually find it. But I think Hal Harris, who was the department head for entomology at that time, probably got the credit for that.

When it moved into Ohio they had established a program to eradicate the corn borer or at least slow it down. The U.S. government had this program where all the corn growers in an area had to destroy their stalks, all of them and then deep plow. I don’t understand their thinking because the corn borer can live in many plants, not just corn. The corn borer can live in maybe as many as 200 different species of plants, so you’re not going to eradicate the corn borer that way. The government spent, I think it was $10 million in the 1930s on this program. The quarantine, burning of stalks and deep plowing didn’t work, like I said, they reached Iowa in 1942. It was considered an epidemic.

Infestation
It was so devastating in the beginning. All of the corn plants were really, really susceptible to the corn borer. C.R. Neiswander who was at Ohio State University told me one day that he found 80 full-grown corn borers in one plant. It’s been recorded in history in Ontario, Canada that there was 40 square miles of corn borers so devastating, that they could not even harvest a single ear of corn. They found 117 full-grown borers in one stalk — 10 borers per stalk is a heavy infestation. If you have 80 or 100 that’s just beyond belief, but that was because the corn genotypes at that time were so susceptible to the pest.

The worst corn borer infestation in Iowa was in 1949. In those days they made a survey of how many borers per plant — I don’t remember how many counties, but I think it was 30. Of the counties polled they averaged eight borers per plant or 800 borers per 100 plants. The corn was down, flat on the ground. I saw fields where all the corn was flattened. There’s a gene in corn called the lazy gene that causes corn to grow flat along the ground — they looked like they had the lazy gene but they didn’t — it was the corn borer.

Another problem with the corn in those days was the susceptibility to stalk rot, and the corn borer is a great inoculator of stalk rot. So if you have a lot of corn borers and a high susceptibility to stalk rot — you have a real bad situation. That’s what some of those fields were like, they had corn borers and stalk rot.

In 1954 in Ohio I was in a field, probably a 40-acre field, where I dissected 10 plants in 30 different locations, that’s 300 plants, every plant was infested. The infestation of those plants ranged from 10 borers to 40 borers per plant. That laid that field low, flat to the ground. There were times where it was worse than that.

The corn borer feeds on the leaves for the first generation, so first generation resistance is actually leaf-feeding resistance. When we would record data on this, I used to have 14,000 first brood nursery plots (10 plants per plot) and 6,000 second generation nursery plots. We would rate the plants on amount of leaf feeding in a scale of 1-9 broken up into 4 categories: 1-2 highly resistant, 3-4 resistant, 5-6 intermediate and 7-9 susceptible. Sometimes, things were so bad I would assign a score of 9 with 10 asterisks behind it. The plant should have been scored a 50, that’s how bad it was.

F.F. Dicke, who was involved in corn borer research for a long time, a great scientist and one of the smartest men I have ever known, died at the age of 95. He and I were the last living people who really knew how bad the European corn borer could really be, we had seen it first hand, and I had only gotten in on the tail end of it.

Program Begins
When you have first-generation resistance, the young larvae die off in the first five days after the eggs hatch. The plants prevent the corn borer from feeding on their leaves. Second generation resistance is a different situation entirely. The corn borer will feed on the collar tissue of the leaf and on the inside of the stalk. In a very bad situation, the sheath will fall off and take the leaves with it while destroying the plants vascular system. The corn won’t be able to photosynthesize and the nutrients pulled up from the roots can’t go anywhere because the inside of the stalk has been destroyed. This is how most of the corn in the 1930s and 1940s was, incredibly susceptible.

So they started a program for breeding for resistance. Professor Dicke was involved in that in Iowa after working in Ohio. George Sprague, an internationally recognized corn geneticist and breeder, was in charge of corn breeding here in Iowa for many years. When the corn borer moved into Iowa, the U.S. government figured they should move the lab here from Toledo, Ohio. The lab in Ankeny, I believe it was 1,800 acres to start with, belonged to the government during World War II as an ordinance plant. They gave that land to Iowa State, as I understand, for a dollar.

My Colleagues
The Corn Insects Research Unit was first known, as the European Corn Borer Lab. Bill Bradley was the first lab leader. Tom Brindley was half-time ISU and half-time USDA-ARS and coordinated research between the department of entomology and the Ankeny lab. The first scientists were: F.F. Dicke, Ken Arbuthnot, Elmer Beck, Dave Questel and L. Patch. Eventually, all of the researchers except Professor Dicke moved to other assignments and Professor Brindley became Research Leader. We all had a lot of fun working for him. He was a great leader.

During my 15-year tenure as research leader, there were six project heads including myself. Les Lewis was in charge of insect biological control, Bill Showers was in charge of insect ecology, Ed Berry was in charge of insecticide, Jerry Klun was in charge of chemical basis of insect resistance in plants and insect pheromone, Bob Lynch and Jim Jarvis were in charge of economic threshold and I was in charge of the plant resistance to insects. This small group of researchers was noted for doing a lot of research with little funds. Many graduate students received their research training in the Ankeny lab.

After I retired, the Ankeny lab was moved to the ISU campus and was combined with other USDA-ARS units. Professor Lewis is research leader of this large group of researchers.

Breeding the borers

So the lab was moved to Ankeny, under Iowa State, in the fall of 1950. I came to Iowa in 1951. I started working with Professor Dicke on breeding for resistance to the European corn borer. In the beginning we didn’t have a good source of moths for egg production. We built three screen cages that were 100 ft. long, 16 ft. wide and 7 ft. high. We filled those cages full of cornstalks that were heavily infested with corn borer. Then in the spring when the corn borer emerged we collected them from those cages and moved them to ones for egg production. Some years we raised 100,000 egg masses. The most we ever got with that system was 500,000 egg masses. An egg mass averages 20 eggs. But when we developed this “meridic diet,” as we called it, we could produce 2 million egg masses for our resistance program and other purposes. By developing meridic (artificial) diet we could produce enough eggs to properly infest our plots each year. Very little, if any, progress could be made relying on natural infestation.

They started the resistance program in the 1930s, but they didn’t do much work on it in the beginning. It really accelerated when we developed a method to rear the corn borer. Then the companies got into this, we’d invite them to Ankeny and show them how to rear the corn borer. Several companies got into breeding for full resistance on a large scale. Some would produce 10 million egg masses a year. That’s a lot of eggs with 20 eggs per mass.

Developing Inbred lines

The amount eggs was no longer a problem, it became how many genotypes we could evaluate each year. Professor Russell and I did a lot of work along with other corn breeders at Iowa State cooperating with the corn breeders in Iowa. This is how any host plant resistance program should be operated — a highly cooperative effort between plant breeders and entomologists. We would evaluate 14,000 plots for first-generation resistance and about 6,000 plots for second-generation resistance. We had to breed for leaf-feeding resistance so we’d infest the plants at the whorl stage of plant development, when they’re about knee high. Then about three weeks later we’d go in and rate the plants on the amount of leaf feeding.

We could usually find first-generation resistance in most plant populations — that was an easy find. It was very difficult to find second-generation resistance; the genetics is different. Corn borer resistance is a quantitatively inherited character. In first generation there are six genes involved and in second there are seven genes involved. We used reciprocal translocations to locate which chromosome arm these genes are on. This means we should not be bothered by biotypes in the corn borer. When I say biotype, I mean a new race.

The resistance to an insect like the Haitian fly is a single gene. Scientists had trouble from the very beginning. They would develop a variety of wheat that would be resistant to the Haitian Fly and within a few years that fly could overcome the resistance. When there’s several genes involved you’re not likely to have that problem. We have not been bothered by biotypes of the borer like they have with the Haitian fly; we’re fortunate that way. The resistance won’t kill every single insect, it might kill 99 percent of them, but there’s still one percent left at any time and that insect will build up a tolerance and overcome the resistance. So you’d call that a new biological race that has developed. We’re fortunate not to have that with the European corn borer.

Results

We developed a number of inbred lines that were used. In Ohio, for example, there was Oh43 and Oh45. Oh43 was used a lot back then. However, when I was working, the average life of an inbred line was only 5-7 years. That’s understandable because you were producing new inbred lines all the time. We even developed some inbred lines that were highly resistant that weren’t used in commercial production because they had drawbacks. D73 was produced by Professor Russell, Arnel Hallauer and Lowel Penny. They discarded that line because of corn borer susceptibility. But, because it yielded so well they later went back and got remnant seed and finally released it.

The only second-generation resistant inbred line was B52. Professor Russell and I crossed it with Oh43, hoping to get some of its first generation resistance in there along with B52 second-generation resistance — it worked. We released that line as B86, it had resistance to both generations. We also had resistant populations from recurrent selection programs. Recurrent selection is used to concentrate several genes and to get as many of those genes into the inbred as possible and that’s why that type of breeding procedure is used. So, Iowa State had material that had resistance to both generations.

Compared to the old days when all the corn was extremely susceptible we made a great advancement to have plants with intermediate resistance — which was of great value to the American farmers.

But with this new technology of putting Bt in the corn plant — I understand that’s a single gene — my guess would be that if every single acre here would be planted with Bt corn, it wouldn’t last more than 10 years and a biotype would develop. I think they are managing it correctly, they don’t plant all acres in Bt corn they plant some to normal corn. I think that will prolong the usefulness of the technology.

I always preached that an insect resistance program is important if it did one thing — it kept from releasing highly susceptible inbred types of corn. We don’t really need really high resistance. On this 1-9 scale, if you have a field that would rate a 5 that’s good. You don’t have to have it completely immune. My thought is that if the corn borer ever manages to overcome the Bt, if companies are not paying any attention to the natural corn borer resistance in time we could get in trouble. Without selecting for natural corn borer resistance we’re going to have things that are as susceptible as they were in the 1930s, ’40s and ’50s again. Every breeding program is an ongoing project; there is no endpoint.

My Life at Iowa State

Now I am a professor emeritus. That just means I’m retired. While I was at Iowa State, a cooperative effort with USDA-ARS furnished our (corn borer personnel) salaries and most of our operating budget. Iowa State furnished some of our operating budget, graduate students, facilities and the utilities. It was a great cooperative effort between the two agencies and I think that’s the way it ought to be done.

I taught a portion of the host plant resistance course. I taught the plant breeding and genetics parts. Most of my time was spent on research. For 15 years, I was the research leader of our little research group, which was made up of five entomologists. Before my time the research leader was just administrative. I continued to do research as well. I also served as a multi-faceted consultant for other country’s plant-breeding programs. Because of my training in entomology, genetics and plant breeding I was often hired as a consultant overseas, advising scientists in all aspects of breeding crop plants for resistance to insects. I served as an adviser in China, Taiwan, Thailand, India, Austria, Bulgaria, Yugoslavia, France, Italy, Switzerland, Israel, Nigeria, Mexico, Kenya, Egypt and the Philippines. I worked with corn, sorghum, cowpeas, chickpeas, rice, yams, cassava and sweet potatoes at various times in various countries.

During the rice project in India I worked with breeders, geneticists and entomologists there. We reviewed their programs and worked with them in the rice fields. I tried to use the model we have at Iowa State to show them how it ought to be done, and then we’d go to the field and write up a report to show them what they could be doing with the rice.

I would brag about the fact that ISU is the best university in the country and I was fortunate to work with the best plant breeders and geneticists in the country. ISU had the best breeding program in the world, because we had the best people. It was a privilege for me as an entomologist to work for that department and the people involved. I always liked everyone there, still do.

I had a 41-year career. If my eyes were still good, I’d probably work 10 more years. It was a great experience being at Iowa State for as long as I’ve been there.