Pesticides:

1. Pesticides: Poisons in the food chain

2. Pesticides • As much as 30% of the annual crop in Canada is lost to pests. • The pests include weeds, rusts and moulds, birds, small mammals, and insects. • For each of these pests, we have created a pesticide. • Pesticides are chemicals designed to reduce the populations of unwanted organisms, both plant and animal.

3. Tires and Mosquitoes • What do we do with worn out old tires? • Can’t bury them in landfills – they just keep popping up. • Can’t burn them – thick choking smoke – bad for the environment • Let them sit???

4. Still water – breeding ground

5. Still Water • The still water – warmed by the sun hitting black rubber, makes an agreeable ecosystem for hatching mosquitoes. • Why is it a problem to create a favourable ecosystem for mosquitoes??

6. Mosquitoes and Disease • Some mosquitoes carry microbes that cause disease. Malaria is one such disease. • Thousands of people in tropical areas of the world die of this disease every year. • Used tires are often stored in one area and then moved to another area for disposal. What problem might this cause?

7. Using Pesticides • Scientists developed a pesticide spray that could eliminate mosquitoes. When it was tried on an island, other effects were soon noted. • Insects other than mosquitoes began to disappear, and then the number of lizards began to fall. • What do you think caused some other insects to begin to disappear? • Why did the lizards begin to disappear?

8. The Problems Spreads • Most people on the island were not too worried about the disappearance of a few insects and some lizards. • However, they took notice once the local wildcats, which had fed on lizards, began to get sick and die. • Without cats the rat population soon increased. • Fearing an outbreak of diseases linked with rats, the local people imported domestic cats. • What problem could be caused by bringing in domestic cats?

9. The Invasion • Changes to the food web became even more obvious when caterpillar populations began to increase • The pesticide affected wasps and other predators of the caterpillar, but had little effect on the caterpillar. • One the predators were gone, the caterpillar population increased greatly. • Eventually hungry caterpillars moved into the fields and devastated food crops

10. Biological Amplification • Pesticides tend to stay in the bodies of animals that come in contact with them. • The result is that the concentration of harmful pesticides increases at each level in a food chain. • Predators always have more toxic chemicals in their bodies than their prey.

11. Biological Amplification • If the body of a prey contains harmful pesticides, the pesticides will be taken in by the predator. • Predators eat many prey over their lifetimes. Each time prey is eaten, the amount of pesticide in the predator increases. • This process is called biological amplification. • Predict how scavengers, such as beetles, might be affected by biological amplification.