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Pests & Bioamplification Foodwebs in Grassland vs. Potato Field Grassland Producers Herbivores Carnivores Food web Potato Field Pests & Bioamplification Foodwebs in Grassland vs. Potato Field Grassland Potato Field Producers 50 – 100 different species of plants Herbivores numerous species of insects, rodents, birds, etc Carnivores numerous species of insects, spiders, snakes, foxes, hawks, etc Food web complex with 100s of species Pests & Bioamplification Foodwebs in Grassland vs. Potato Field Grassland Potato Field monoculture of potato Producers 50 – 100 different species of plants Herbivores numerous species of insects, rodents, birds, etc Carnivores numerous species of insects, spiders, snakes, foxes, hawks, etc Food web complex with 100s of species plants. Other plants considered weeds few such as Colorado potato beetle, considered pests very few, if any food web effectively eliminated Pests & Bioamplification Pesticide: a substance used to kill a pest herbicides kill plants insecticides kill insects fungicides kill moulds etc Pests & Bioamplification Pesticide: a substance used to kill a pest herbicides kill plants insecticides kill insects fungicides kill moulds etc Broad-spectrum pesticide: effective against many types of pests e.g. DDT is toxic to most insect species Narrow-spectrum pesticide: effective against only a few types of pests e.g. Bt, a modern pesticide from bacteria is toxic only to caterpillars Pests & Bioamplification How pesticides work: 1. Physical harm: diatomaceous earth scratches the waxy outer coating of insects so they dehydrate Pests & Bioamplification How pesticides work: 1. Physical harm: diatomaceous earth scratches the waxy outer coating of insects so they dehydrate 2. Biological harm: some herbicides interfere with photosynthesis Pests & Bioamplification Issues with pesticides: 1. Non-target species: pesticides often kill species they were not intended to kill e.g. a broad-spectrum insecticide may kill predatory insects that normally feed on pests Pests & Bioamplification Issues with pesticides: 1. Non-target species: pesticides often kill species they were not intended to kill e.g. a broad-spectrum insecticide may kill predatory insects that normally feed on pests 2. Bioaccumulation: the increasing concentration of a pesticide as it moves up the food chain e.g. DDT is a long-lasting insecticide that wiped out song bird populations in the 1960s Pests & Bioamplification Bioaccumulation: e.g. DDT leached into a lake from fields herring gull egg (6.3 ppm) smelt (0.43 ppm) (fish) freshwater shrimp (0.03 ppm) ppm = parts per million Pests & Bioamplification Persistent chemicals: the bioaccumulation occurred because these pesticides lasted a long time in the environment and could be passed up the food chain -today pesticides are developed to break down quickly to avoid this buildup Pests & Bioamplification Pesticide Resistance: when a species targeted by a pesticide are no longer affected by it. -happens by chance mutations of DNA -once it occurs, these individuals with resistance produce the most offspring and the resistance quickly spreads to the entire species -the more frequently the pest reproduces, the faster resistance will develop Pests & Bioamplification Organic Farming: the system of agriculture that relies on non-synthetic pesticides and fertilizers Integrated Pest Management: a system that uses a combination of physical, chemical, and biological controls method example biological control predatory insects, disease causing microorganisms altered timing planting & harvesting to avoid peak pest populations crop rotation, avoiding monocultures in the same location mixed planting year after year baiting pests pheromone (sex hormone) baits can be used to confuse some mating insects