Integrated pest management| Land and Water Use| AP Environmental science| Khan Academy

Let's imagine you're a corn farmer and you would dream of having a nice, healthy corn crop like we see in this picture.

But being a farmer isn't as simple as planting the seeds and making sure that the crop gets enough sunshine, water, and fertilizer. You also have to deal with pests. Pests can be viewed as anything that might eat your crop, destroy your crop, or make it just really hard for you to have a good crop.

Now, some of you all are familiar with the notion of pesticides, where you're essentially poisoning the pests. For various reasons, that might not be a good idea, and we'll talk more about it. There's a notion of integrated pest management, which is how we can do multiple things that might include pesticides or might not include pesticides to really keep things under control.

To get a good sense of how bad a pest can be, I will introduce you to the western corn root worm. The reason why it's called a worm, even though its adult face does not look like a worm, is that in its larval phase, when it's a baby, it looks like a worm. Even though the adult will also feed on the corn silks, the real damage is done in the larval stage when they're feeding on the roots. That's why they're called corn root worms.

The USDA estimates that just in the United States, damage due to the western corn rootworm is about 1 billion dollars per year. About 800 million of that is just lost corn crop, and about 200 million of that is all the cost in order to prevent this pest from doing its damage.

As I mentioned, if we're thinking about integrated pest management, there are many ways of addressing this. One way, of course, that many people think of is pesticides. This is an image of crop dusting. I don't think this is a cornfield here, but you can see the pesticides coming from the biplane. It's a way of spreading the pesticides—it's not the only way—but for various reasons, this is not optimal.

You could view it as polluting the environment in certain ways. A lot of us aren't so keen on eating crops that have pesticides on them. And we've learned in other videos on evolution and natural selection that there's variation in any population. The more you expose a population to something and it kills off the ones that are susceptible, the more chances that the ones that aren't as susceptible reproduce and thrive.

At some point, you might have an insecticide-resistant pest on your hands, and then your insecticide isn't going to be all that useful. So when we think about integrated pest management, we think about what are other ways to address this, maybe in conjunction with ways that could be perceived to be more natural.

Well, one obvious thing is to think about what are the predators of that pest. This is the wasp spider and this is what's known as a ladybug in North America and a ladybird in much of the rest of the world. They will actually feed on the western corn rootworm, so you might want to introduce this onto your farm if you're trying to grow that corn.

Another thing that farmers have done to some degree of success is early planting. By planting the crop early, it's less favorable for the rootworm to lay their eggs, and it gives a chance for the roots to get stronger so that by the time that they're attacked by the rootworm, they're going to be more resilient.

You could also have hybrid versions of corn that just have larger roots, so once again, they're going to be more resilient to the rootworm. Another technique is to genetically modify the corn, and that also is a bit of a controversial topic. Depending on who you talk to, you might have heard things about GMO—genetically modified organisms. Some people think they're fine; some people are wary of them.

But there is a transgenic version of corn. Transgenic means that we took DNA from some other organism and put it into the corn. That transgenic version is known as Bt corn. It actually has DNA from a bacteria which produces a protein that is harmful to certain types of root worms.

Now, another really interesting technique, which people have used to some degree of success, is known as crop rotation. Let’s imagine we're looking down from the sky onto a corn crop here. So, we're looking down from above.

What normally happens is that the eggs are laid near the corn, and the larvae can't travel so far. So, if they're near the corn, they get to the roots, and then the reproduction cycle goes on. But if we rotate the crops so that next year we're not planting corn here, but maybe we are planting the corn over here, and then in that first place, we're planting soybean, well that can solve the problem.

The eggs will be laid here, but next year the corn is going to be here, and over here we will have the soybean, which is not a suitable food for the corn rootworm. Now what's really interesting—this is another one of those fascinating stories of evolution and natural selection—are there cases because there's variation in populations where some of the adult rootworms actually don't lay their eggs in the same corn crop where they feed? They lay it in an adjacent corn crop so that next year when the crop rotation happens, then their larvae are going to have access to the corn in the other field.

You might say, “How did they know that? How did they know that the farmers were planning to rotate?” Well, generally, the rotations are pretty simple. You keep alternating between two crops like corn and soybean. Most of the western corn rootworm would not have done that, but just some of them might have started to randomly travel a little bit further, and then those would be more likely to reproduce.

So the ones that are more likely to reproduce will then exist more, and that behavior would be passed on if it is a genetic trait. There are other situations, once again because of variation in populations, where some of the eggs stay dormant for an extra year. So, even though you might rotate to corn this year, the year after that you rotate back to corn, and then the eggs hatch and the larvae could feed.

So, it's a fascinating almost arms race between the farmer and these pests. But I hope you appreciate it's far more interesting than you might have realized before. I haven't even given you a comprehensive list of all the types of pests and all of the ways that you might want to manage them.

You can do physical removal. You can do barriers. Maybe you'll think of another creative way to have integrated pest management.