Grade 9 Science Ms. Brothers There are no pests in nature it is all subjective Organisms that might compete or damage crop species (reduce yield) Weeds, mosquitoes, mice When farmers plant a monoculture, they create the ideal environment for pests Colorado potato beetles A substance (poison) to kill pests Herbicides plants Insecticides insects Rodenticides rodents (mice) Fungicides fungus Molluscicides snails Piscicides fish 1. Long-lived: lasts many years E.g. synthetic pesticides 2. Short-lived: lasts a few days E.g. Natural pesticides 3. Broad-spectrum: toxic to wide range of species E.g. DDT: Insecticide; toxic to MOST insect species 4. Narrow-spectrum: toxic to a limited # of species E.g. Bt (Bacillus thuringiensis): Insecticide; toxic to only caterpillars, beetle larvae, fly larvae Physical harm E.g. diatomaceous earth: abrasive powder scratches outer coating of small organisms Chemical harm E.g. interfere with photosynthesis; damage vital organs, etc. Direct Delivered by contact: pest must touch pesticide Indirect e.g. herbicide that is sprayed on the grass will only take effect once it is taken up by the roots of the weed. 1. Non-target species Broad-spectrum pesticides will kill species that were not intended to be killed Might even kill potentially beneficial organisms, i.e. Predatory insects that normally feed on pests Thereby causing farmers to be more dependent on pesticides Other examples: - Honeybees killed unable to pollinate fruit crops - DDT to kill mosquitoes (reduced spread of malaria), but also killed wasps. The wasps ate thatch-eating caterpillars, and since their predator was killed, they ate the villagers thatch roofs. 2. Bioamplification The concentration of pesticide that accumulates in the body of an organism Pesticides that bioaccumulate do so because they cannot easily be excreted from the body. If a pesticide bioamplifies in a food chain, it may reach toxic concentrations E.g. DDT, mercury, PCBs 3. Pesticide resistance When pesticides are used for long periods of time, it might lose its ability to control the pest. Individuals will survive an application of pesticide, and will reproduce and pass on their resistance to their offspring After many generations, the population can become highly resistant to a particular pesticide 3. Pesticide resistance continued... Global scale: pesticide resistance is a serious concern Farming without the use of synthetic pesticides or fertilizers Accept crop losses Higher prices for products Control: Biological Altered timing Crop rotation & mixed planting Baiting pest We can reduce our dependence on pesticides by using organic farming in combination with other types of management methods The goal: To maximize efficiency Keep costs low Reduce harm to the environment