How can chemical signals help farmers? It’s night-your favorite time-and you’re flying through a field of tomatoes. You’re a fuzzy, brown cabbage looper moth, a male of your species. Suddenly your antennae pick up an irresistible fragrance. The message shrieks like a siren: Female! Female! Female! You make a beeline-oops, a mothlinetoward the smell. Finally, you land in this strange-looking cardboard box. Hmmm. Other males are in here, but, hey, where’s the female? You have been trapped by two tomato farmers with a keen interest in cabbage loopers, beet army worms, and other tomato pests.
Science and Farming(Getting The Bugs Out)
The tomato farmers are a husband-and-wife team who are working with scientists to find ways to reduce the amount of chemicals people put on crops. They catch male cabbage loopers by attracting them into traps that are baited with sex pheromones of female cabbage loopers. The farmers count the male moths in the pheromone traps. The count helps farmers determine how many female moths are in the field laying eggs on the tomatoes. The eggs will hatch into larvae that will worm their way into the farmers’ tomatoes.
If the numbers of trapped males are high, the farmers will apply insecticide to control the cabbage looper larvae. If the numbers are low, no insecticide is necessary. Scientific knowledge about plant chemical signals can also be put to work in fields and gardens. For years, farmers and gardeners have used sprays containing pyrethrums as insecticides. With more research, scientists and farmers may find that the alarm chemical made by sagebrush plants can be useful. By spraying the chemical on fields, crops might begin to make the chemicals that protect them from plant-eating insects. Today, more than ever before, scientists and farmers are working together to use what they know about plants and insects. Their work is helping find better ways to grow crops, such as the enormous wheat crop shown below. Thanks to their work, you can leave a grocery store with a shopping cart filled to the brim with tasty, nutritious foods!
The Age of DDT
Ever since farming began 8000 years ago, people have been trying to get rid of insects and other crop pests. Early methods of pest control were hard work. People tried trapping insects, swatting them, and scaring them away. In some parts of the world entire villages still tramp through the fields beating drums to scare off grasshoppers. A history of pest control methods is shown
in the timeline on the next few pages. Follow the dates and pictures as you read. In the 1800s, people began to use chemicals to kill insect pests. A chemical that kills pests that damage crops is a pesticide (pes’to sid). Back in the 1800s, most pesticides contained metals, such as arsenic, copper, and mercury. Some of these pesticides can be very poisonous. They often killed the plants as well as the insects!
In 1939, an accidental discovery made people in this century very dependent on pesticides. In that year, Swiss chemist Paul Muller discovered that a chemical called DDT killed moths that ate wool clothes. So he began to investigate DDT. Muller found that DDT was a powerful insecticide that killed many other kinds of insects.
During World War II, DDT was used to kill disease-carrying insects such as head lice and mosquitoes. DDT saved thousands of soldiers who would have died of diseases, such as typhus and malaria, that these insects carry. Shortly after the war, Paul M?ller won a Nobel Prize for his lifesaving discovery. In the 1950s, people turned their attention to a peacetime problem-how to produce food for the world’s growing population. Farmers began to use DDT in their fields. At first, people were very excited about the new “wonder” chemical. Farmers discovered that DDT killed a wide variety of crop pests. But that’s not all. DDT was also cheap and easy to use. It wasn’t long before farmers were using DDT on everything. Harvests were gigantic! It looked as if the problem of feeding the world was solved. But slowly people began to realize that DDT affected more than just insect pests. By the 1960s, people began to see that DDT was poisoning everything the soil, rivers, lakes, wildlife, and people!
A New Day in Pest Control
The timeline on this page continues to 1972-an important date in the history of pest control. In 1972, a law was passed that made the use of DDT illegal in the United States. People’s views about pesticides were changing. By that time a great deal of evidence showed that DDT was harming the environment. And the poisonous effects of DDT lasted a long time. Studies also showed that DDT wasn’t working anymore. Malaria was on the rise again. Why? Mosquitoes that carried malaria had developed resistance to DDT the pesticide no longer had any effect on them.
Crop pests were also becoming resistant to DDT. The more the farmers applied DDT, the less it worked. Heavy use of DDT was causing more and more insects to become resistant to the chemical. Farmers were also discouraged to find that their fields had greater numbers of pests than ever before. What was going on? For one thing, DDT was also killing the natural enemies of insect pests. With their enemies wiped out, the populations of the pests could increase rapidly.
But what has happened since 1972? Many chemical pesticides quickly replaced DDT, but they have the same problems. Many of these pesticides harm the environment. In fact, some of these chemicals are even more poisonous than DDT. And, as you can see in the graph. many kinds of insects have developed resistance to pesticides. Of these resistant species, many are disease carrying insects and serious crop pests. For more than 50 years, people have been waging all-out chemical warfare against insects. At one time, people believed fthat chemical pesticides would solve the problem of producing food for the world’s growing population. But sometimes crop losses are just as high as they were before so many chemicals were used. By now, you probably wonder, “Who’s winning this war?” Solving the problems of pest control is an exciting challenge for scientists and farmers. How can they develop new chemicals and methods that do the job safely and inexpensively-and still grow enough food for people everywhere?
Many farmers are using smaller amounts of chemicals. Farmers are also applying chemicals to their fields less often. And some farmers, called organic farmers, don’t use any chemicals at all. Farmers are also using biological pest control. A biological control is a method that uses natural enemies to control insects. As you read on, you will see that biological control is one way farmers can work with, not against, nature.
