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• Monocultures offer ideal living conditions and allow high reproduction rates for herbivores
• Populations of insects grow more quickly and are normally more mobile compared to mice, which is why their impact on crops is extremely serious
• Insecticides


  Chemical pest control
• Insecticides can be problematic

  Potential toxicity of insecticides or their decomposition products
• Insecticides do not always show the desired effect of protecting plants


  These substances interfere with the food web at various positions
• Most predators of pest insects are also themselves arthropods (e.g. spiders), their populations might concomitantly be reduced if the insecticide is not sufficiently pest-specific
• Predator population recovers more slowly than the pest populations after the application of insecticides


  Because of their lower rate of growth
• Larvae of the cotton worm live in the stems and capsules of cotton plants (leaf miners) and can significantly affect the yield of a crop
• Trying to control cotton worm larvae by externally sprayed-on insecticides is difficult as little of the insecticide reaches the pests
• Predatory insects and spiders preying on the cotton worm however live on the surface of the plants and therefore are directly affected
• Transgenic plants


  Plants genetically modified to produce insecticides by themselves
• Bacillus thuringiensis is a bacterium whose genes enable plants to synthesise toxins that do not affect vertebrates, preying insects or spiders, but that are lethal for herbivorous insects
• The use of transgenic plants is however not unequivocal
• The frequent application of the same substances can lead to the survival and unrestricted proliferation of any individuals that happen to be resistant to these substances, which then lose their effect
• This is especially true for transgenic plants as they permanently produce the same insecticide
• Fungicides


  Used against parasitic fungi that can reduce crop yields
• Arable land offers ideal living conditions to both the crop plants and to fast-growing plants such as hemp nettle, knotweed and other "weeds" that compete for limited resources such as space, light and minerals
• In order to avoid smaller crop yields, herbicides are applied
• Not only the competing plants, but also useful insects disappear as their larvae often depend on these types of "weed" as their food source
• Population ecology


  The study of how populations of organisms interact with their environment
• Pest management


  The control or regulation of pest populations
• Population ecology and pest management


  Are closely linked, especially in agricultural contexts
• Growth of food crops

  Can be heavily impacted by herbivores (termed "pests") and competing plants (termed "weeds")
• Insecticides


  Chemicals used to control pest populations
• Monoculture farming


  Provides ideal conditions for herbivores, leading to rapid reproduction rates
• Insect populations


  Can grow quickly and have a significant impact on crops
• Use of insecticides


  • Potential toxicity and unintended effects on non-target organisms, disrupting the food web
  • Recovery of predator populations is slower than that of pest populations after insecticide application
• Cotton worm larvae


  Difficult to control with external insecticide applications
• Predatory insects and spiders

  Can be adversely affected by insecticide applications
• Genetic modification of plants

  Plants can be modified to produce insecticides internally
• Bt corn


  • Contains genes from the bacterium Bacillus thuringiensis, allowing the plants to synthesize toxins lethal to herbivorous insects while sparing non-target organisms
• The use of transgenic plants is controversial
• Repeated use of the same insecticide

  Can lead to the development of resistance in pest populations
• Fungicides


  Chemicals used to control parasitic fungi
• Herbicides


  Chemicals used to control competing plants ("weeds")
• Use of herbicides


  Can lead to the disappearance of useful insects that rely on these "weeds" as a food source
• Managing pest populations involves a combination of chemical and biological methods
• Careful consideration of the potential impacts on ecosystems and the development of resistance among pest populations is required
• More than 90% of central Europe used to be covered by forest
• Forests are still of great importance to us: wood is a renewable resource