Pests, Pesticides & Issues with Pesticides

Pests: Organisms that compete with or damage crop species (e.g., weeds, mosquitoes, mice).
Controlling pests allows crops to grow in abundance.
Pesticides: Substances used to kill pests.
- Herbicides: Kill plants.
- Insecticides: Kill insects.
- Rodenticides: Kill rodents.

Persistence: Pesticides vary in how long they remain active in the environment (from days to years).
Spectrum of control: Pesticides vary in the number of species they can control.
- Broad-spectrum pesticides: Toxic to a wide range of species.
- Narrow-spectrum pesticides: Toxic to a limited number of species.

Pesticides cause physical or biological harm to the pest organism.
- Physical Harm Example: Diatomaceous Earth (fossilized algae remains) scratches the waxy outer coating of insects, causing dehydration.
- Biological Harm Examples: Interference with photosynthesis or damage to vital organs.

DDT
- Origin: Synthetic
- Use: Broad-spectrum insecticide
- Characteristics:
  - One of the first widely used synthetic pesticides.
  - Highly persistent in food chains, causing die-off of predatory birds.
  - Widely banned in the 1970s but still used in some countries to kill mosquitoes that transmit malaria.
Rotenone
- Origin: Natural toxin extracted from plant roots
- Use: Insecticide and piscicide
- Characteristics:
  - Highly toxic to many aquatic organisms, including fish.
  - Approved for use by some organic farmers.
Glyphosate
- Origin: Synthetic
- Use: Broad-spectrum herbicide
- Characteristics:
  - Widely used herbicide.
  - Very low persistence.
Bt (Bacillus thuringiensis)
- Origin: A protein obtained from the bacteria Bacillus thuringiensis
- Use: Narrow-spectrum insecticide
- Characteristics:
  - Highly toxic to moth and butterfly caterpillars.
  - Safer than most pesticides.

Benefits:
- Reduce crop damage from pests.
- Increase food production.
- Control populations of biting insects that spread diseases.
Environmental Costs: While pesticides result in more food and better health, their use has many environmental costs.

Pesticides are often applied through aerosols or sprays onto fields, forests, and gardens.
A significant portion of the pesticide never reaches the target species due to air currents or landing on the soil.
These pesticides become potential sources of soil, water, and air pollution.
Pesticides can also harm non-target species.

Pesticides often kill species they were not intended to kill.
Broad-spectrum pesticides may kill non-damaging and potentially beneficial organisms.
Improper use of pesticides may kill non-target species (e.g., spraying insecticide at the wrong time of year may kill honey bees).
Killing non-target species can have surprising and serious consequences.
- Borneo Example (1955):
  - WHO used DDT to control mosquitoes spreading malaria.
  - DDT killed wasps that preyed on thatch-eating caterpillars.
  - Caterpillars ravaged villagers' thatched homes.
  - DDT also killed cockroaches consumed by lizards.
  - DDT damaged the nervous system of lizards, making them easy prey for cats.
  - Many cats died from consuming poisoned lizards.
  - The rat population increased dramatically due to the disappearance of cats.
  - Fleas on rats carried the plague.
  - Large numbers of replacement cats were brought to Borneo to control the rats (Operation Cat Drop).

Pesticides can accumulate in individual organisms because they are not broken down or eliminated with body waste.
Bioaccumulation: The process where an individual continues to accumulate pesticides in the body by eating contaminated food.

Organisms are part of a food chain; toxins stored in fats and oils are passed on to the next trophic level.
Bioamplification: The process where pesticides become more concentrated higher up the food chain.
Pesticide concentrations can reach toxic levels through bioamplification.
Example: Concentration of DDT increasing more than 600 times in a food chain.

Pest species may become resistant to pesticides when they are used for long periods.
Pesticide resistance means the pesticide is no longer able to control the pest.
Individuals with the greatest resistance survive and reproduce, passing on their resistance to their offspring.
When resistance develops, farmers must apply a greater concentration of the pesticide or switch to a different pesticide.

Organic Farming: Agriculture that relies on non-synthetic pesticides and fertilizers.
Integrated Pest Management (IPM): A strategy to control pests that uses a combination of physical, chemical, and biological controls.

Biological control:
- Predatory insects, mites, and disease-causing micro-organisms prey on and infect pest species.
- Examples: parasitic wasps and ladybird beetles (ladybugs).
Altered timing:
- Better timing of planting and harvesting can avoid peak pest populations.
Crop rotation and mixed planting:
- Pest populations do not have the same opportunities to establish and prosper when farmers do not grow monocultures in the same location year after year.
Baiting pest:
- Pheromone baits can be used to confuse some mating insects.