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Pest Control
Methods

Explore chemical, biological, and integrated approaches to managing pest populations, and understand their environmental trade-offs.

AP Environmental Science

What Is a Pest?

A pest is any organism that interferes with human activities: damaging crops, spreading disease, or competing for resources. Pests include insects, weeds, fungi, rodents, and even invasive species.

Why Pest Control Matters

Food Security
Pests destroy roughly \(20-40\%\) of global crop production annually, threatening food supply chains.
Human Health
Vector-borne diseases like malaria (mosquitoes) and plague (fleas) kill hundreds of thousands each year.
Ecosystem Balance
Invasive pest species disrupt native ecosystems, outcompeting local organisms and reducing biodiversity.

The Three Major Categories

Chemical Pesticides Herbicides Fungicides Insecticides Fast-acting Broad-spectrum Environmental risk Biological Natural predators Parasitoids Pathogens (Bt) Sterile males Species-specific Slower onset Lower toxicity IPM Monitoring Cultural practices Biological + Chemical Threshold-based Holistic approach Cost-effective Most sustainable

Chemical Pest Control

Chemical pest control uses synthetic or natural toxins to kill, repel, or inhibit pests. These include insecticides (target insects), herbicides (target weeds), fungicides (target fungi), and rodenticides (target rodents).

1
Broad-spectrum pesticides kill many species, including non-target organisms like pollinators and soil microbes.
2
Narrow-spectrum pesticides target specific species, reducing collateral ecological damage.
3
Persistent pesticides (e.g., DDT) remain in the environment for years, leading to bioaccumulation and biomagnification.

Bioaccumulation and Biomagnification

Producers (Plants) Primary Consumers Secondary Consumers Apex Predators
\(0.01\,\text{ppm}\)
\(0.1\,\text{ppm}\)
\(1\,\text{ppm}\)
\(10\,\text{ppm}\)
 Increasing concentration

The Pesticide Treadmill

Apply pesticide Susceptible pests die Resistant pests survive Resistant pop. reproduces Cycle repeats: stronger pesticide needed

Biological Pest Control

Biological control uses living organisms to suppress pest populations. This mimics natural ecological relationships, typically predator-prey or host-parasite dynamics.

Predators
Ladybugs eat aphids; barn owls hunt rodents. Introduced predators can reduce pest numbers naturally.
Parasitoids
Parasitic wasps lay eggs inside pest larvae, killing them as the wasp develops. Highly species-specific.
Pathogens
Bacillus thuringiensis (Bt) produces toxins lethal to specific insect larvae but harmless to most non-target species.

Chemical vs. Biological Control

Chemical Biological
Speed of action Fast (hours to days) Slow (weeks to months)
Specificity Often broad-spectrum Usually species-specific
Resistance risk High: pests evolve quickly Low: co-evolutionary arms race
Non-target effects Significant: pollinators, soil life Minimal if well-chosen
Persistence Can bioaccumulate Self-regulating
Cost pattern Recurring purchases One-time + monitoring

Integrated Pest Management (IPM)

IPM is a holistic, threshold-based strategy that combines multiple pest control methods while minimizing environmental harm. It is considered the gold standard by the EPA and AP Environmental Science curriculum.

Prevention & Cultural Controls Monitoring & Thresholds Biological Controls Chemical First Second Third Last resort

Control methods act at different points in pest ecology

Crop mesh,parasitoid-caterpillar interaction and directed pest treatment in a cabbage setting.Pest controls can interrupt host availability, exclude pests physically, use natural enemies, or apply a directed treatment. Effective choices depend on the pest, host, timing and non-target effects.

Pest controls target different mechanisms

Pest controls target different mechanisms. Pest controls can interrupt host availability, exclude pests physically, use natural enemies, or apply a directed treatment. Effective choices depend on the pest, host, timing and non-target effects.Pest controls can interrupt host availability, exclude pests physically, use natural enemies, or apply a directed treatment. Effective choices depend on the pest, host, timing and non-target effects.

How to Apply IPM

1
Identify the pest. Accurate identification prevents treating the wrong organism or misapplying controls.
2
Monitor and scout. Regularly inspect fields or areas to measure pest population levels.
3
Set action thresholds. Determine the pest density at which economic damage justifies intervention (the Economic Threshold).
4
Use cultural and mechanical controls first: crop rotation, intercropping, physical traps, and habitat manipulation.
5
Deploy biological controls if thresholds are exceeded: natural predators, parasitoids, or Bt.
6
Apply targeted chemicals only as a last resort, using the narrowest-spectrum pesticide available at the lowest effective dose.

The Economic Threshold

Time Pest Population EIL ET Treat Treat

Case Study: DDT and Bald Eagles

DDT was widely sprayed to control mosquitoes in the mid-20th century. As a persistent, broad-spectrum organochlorine pesticide, it entered aquatic food chains and biomagnified up to apex predators.

1
Sprayed on wetlands to kill mosquito larvae. DDT entered water at \(0.000003\,\text{ppm}\).
2
Phytoplankton absorbed DDT, concentrating it to \(0.04\,\text{ppm}\).
3
Fish accumulated further to \(2\,\text{ppm}\) in their fatty tissues.
4
Bald eagles reached \(25\,\text{ppm}\), causing eggshell thinning and population crashes. DDT was banned in the U.S. in \(1972\).

Case Study: Cactus Moth in Australia

In the 1920s, prickly pear cactus (Opuntia) had invaded over \(24\) million hectares of Australian farmland. Chemical control was impractical at this scale.

✓ Pros
Self-sustaining, no chemicals needed, extremely cost-effective long-term.
✕ Risks
The moth later spread to the Americas, threatening native Opuntia species: an unintended consequence of biocontrol.

Genetic Control: Sterile Male Technique

Lab Irradiate male insects Release Sterile males into wild Mate Females mate with sterile males No viable offspring

Common Mistakes

✕ Confusing bioaccumulation with biomagnification
Bioaccumulation is within one organism over time. Biomagnification is concentration increasing across trophic levels.
✕ Saying IPM avoids all chemicals
IPM does not ban chemicals: it uses them as a last resort after cultural, mechanical, and biological methods are tried.
✕ Assuming biological control has no risks
Introduced biocontrol agents can become invasive themselves (e.g., cane toads in Australia). Always assess non-target effects.

Pest Control Summary

Method Chemical Biological IPM
Approach Synthetic toxins Natural enemies Combined strategies
Effectiveness Rapid, powerful Gradual, sustained Balanced, adaptive
Resistance risk High Low Low
Ecosystem impact High Variable Minimal
Cost over time Increasing (treadmill) Low after establishment Cost-effective
AP Exam focus DDT, biomagnification Bt, predator-prey Threshold concept

Question 1 of 5

A farmer notices that the concentration of a pesticide increases at each successive trophic level in a nearby lake ecosystem. This phenomenon is best described as:

Question 2 of 5

In Integrated Pest Management, which step is performed first?

Question 3 of 5

The "pesticide treadmill" describes a situation where:

Question 4 of 5

A scientist releases sterilized male screwworm flies into a wild population. This technique is an example of:

Question 5 of 5

Which statement about biological pest control is most accurate?