AP Environmental Science

## Learning Outcomes

- Explain why integrated pest management aims to control pests rather than eliminate them
- Identify the main tradeoffs between IPM and routine pesticide use
- Distinguish between economic threshold and economic injury level
- Compare biological, cultural, mechanical, and chemical controls within an IPM plan
- Explain how IPM can reduce pesticide resistance, non-target harm, and pollution
- Apply IPM tradeoff reasoning to AP Environmental Science exam questions

## AP Environmental Science Syllabus

For the AP Environmental Science, you are expected to understand integrated pest management tradeoffs, with a focus on the following syllabus points:

- Know that **integrated pest management (IPM)** combines multiple pest-control methods and uses chemical pesticides as a later option
- Understand that IPM aims to keep pest populations below damaging or economically unacceptable levels, not to eradicate every pest
- Identify the benefits of IPM, including reduced pesticide use, reduced non-target effects, and slower development of pesticide resistance
- Explain the costs or limitations of IPM, including increased monitoring, labor, knowledge, time, and short-term expense
- Distinguish between **economic threshold (ET)** and **economic injury level (EIL)**
- Compare the tradeoffs of biological, cultural, mechanical, and chemical controls
- Understand how broad-spectrum pesticide use can cause resistance, pest resurgence, and the **pesticide treadmill**
- Apply IPM to agricultural scenarios involving monitoring, thresholds, and evidence-based decisions

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. Why does IPM allow some pest presence instead of trying to eliminate all pests?
2. What is the difference between an economic threshold and an economic injury level?
3. How can repeated use of one pesticide lead to resistance?
4. Why might a farmer choose IPM even if pesticide spraying seems faster?
5. Name one benefit and one drawback of biological control in an IPM plan.

## Introduction

Integrated pest management is one of the key sustainability ideas in Unit 5 because it asks a basic APES question: how can humans protect crop yields without causing unnecessary environmental damage? Pest control is not just about killing insects. It affects food supply, soil organisms, pollinators, water quality, human health, and long-term farm sustainability.

AP Environmental Science often tests IPM through tradeoffs. A student may know that IPM is “better for the environment,” but that is not enough. You need to explain _why_ it is better, _when_ it is better, and _what costs come with it_. That means thinking about timing, monitoring, labor, economics, and ecology together.

> **Key Term: integrated pest management (IPM)**
> An ecological-based pest control strategy that combines monitoring, thresholds, prevention, and multiple control methods to keep pest populations below damaging levels rather than eliminate them completely.

### Why IPM exists: the problem with pesticide-only control

Chemical pesticides can clearly work in the short run. They can reduce pest numbers quickly, protect crops, and lower immediate crop loss. That is why they became a major part of industrial agriculture and the Green Revolution. But APES expects you to know that this success comes with major environmental costs.

One problem is inefficiency. Only a small proportion of pesticide actually reaches the target pest. The rest may remain in soil, drift in air, wash into waterways, or contact organisms that were never meant to be exposed. This creates risks for pollinators, predators of pests, birds, aquatic organisms, and humans.

Another problem is selection pressure. If a pest population has genetic variation, a few individuals may survive exposure to a pesticide. Those survivors reproduce. Over time, the population becomes less susceptible to the chemical. This is evolution by natural selection in real time.

> **Key Term: pesticide resistance**
> The decreased susceptibility of a pest population to a pesticide that was previously effective, caused by natural selection favoring resistant individuals.

If farmers respond to resistance by spraying more often or using higher doses, the system becomes self-defeating. Costs rise, ecological damage rises, and control often becomes weaker over time.

> **Key Term: pesticide treadmill**
> A cycle in which pesticide use selects for resistant pests, leading to heavier or repeated pesticide use, which then worsens resistance and environmental harm.

IPM exists because pesticide-only control often treats the symptom, not the system. If a field has low biodiversity, weak predator populations, continuous monoculture, and poor monitoring, pests are more likely to become serious in the first place. IPM tries to change those conditions.

Cause-and-effect chain that students should be able to explain:

- Heavy use of one pesticide
- Strong selection for resistant pests
- Resistant individuals survive and reproduce
- Future spraying becomes less effective
- Farmers spray more or switch chemicals
- Costs and environmental damage increase
- Long-term control becomes harder
  > **Test Tip:** On FRQs, do not just say “pests become resistant.” Explain the natural selection process: variation exists, susceptible pests die, resistant pests survive, and their alleles become more common.

### The core tradeoff: better long-term sustainability, greater short-term complexity

The main tradeoff of IPM is simple to state but needs careful explanation: IPM usually reduces environmental harm and improves long-term sustainability, but it often requires more monitoring, more expertise, more labor, and more patience than routine spraying.

IPM starts with correct pest identification. That matters because not every insect in a field is a pest. Some are pollinators. Some are predators of pests. Some do no meaningful damage at all. Misidentification can lead to unnecessary treatment or the wrong treatment.

IPM also depends on monitoring, sometimes called scouting. Farmers inspect crops, count pests, look for eggs or larvae, check traps, and keep records. This makes IPM data-based rather than automatic.

That sounds sensible, but it costs time and labor. A farmer using calendar-based spraying can simply apply a pesticide on schedule. A farmer using IPM must first inspect, identify, compare numbers to thresholds, choose a method, and later evaluate whether it worked.

> **Key Term: monitoring (scouting)**
> The regular inspection of crops or areas for pests, damage, and beneficial organisms in order to decide whether action is needed.

This is why IPM can seem less attractive in the short term, especially where labor is expensive or expert advice is limited. But the long-term benefits can be large:

- reduced pesticide runoff into streams and lakes
- reduced harm to pollinators such as bees
- reduced killing of natural predators such as ladybugs or parasitic wasps
- slower evolution of resistance
- lower risk of bioaccumulation and biomagnification from persistent chemicals
- lower risk to farm workers and nearby communities

The exam often rewards balance. A strong answer does not claim IPM is always easy or always cheap. It shows that IPM may raise short-term management costs while lowering long-term ecological and economic costs.

A useful comparison:

- **Routine pesticide use:** fast, simple, scalable, but higher risk of resistance and non-target damage
- **IPM:** slower to plan and manage, but usually more sustainable and less damaging

### Thresholds, thresholds, thresholds: why IPM does not mean zero pests

One of the most misunderstood points in IPM is that success does not mean zero pests. In fact, some pest presence is acceptable. This is because the cost of eliminating every pest may be greater than the cost of tolerating low-level damage.

> **Key Term: economic threshold (ET)**
> The pest population level at which action should be taken to prevent the population from reaching the economic injury level.
>
> **Key Term: economic injury level (EIL)**
> The lowest pest population density at which economic damage equals the cost of controlling the pest.

The distinction matters:

- **EIL** is the damage point
- **ET** is the action point before that damage point is reached

So if an FRQ asks why a farmer might wait before spraying, the answer is not “because they do not care about crop damage.” The better answer is that spraying below the threshold may waste money, increase environmental harm, and kill beneficial organisms without enough benefit.

Worked example:

Suppose a pest begins to appear in a tomato field.

- At 2 insects per plant, crop damage is minor
- At 8 insects per plant, expected crop loss would equal the cost of spraying
- The farmer sets action at 6 insects per plant to avoid reaching 8

In this case:

- **EIL = 8 insects per plant**
- **ET = 6 insects per plant**

The grower acts at 6, not at the first sighting and not after severe visible damage.

This is why monitoring is central to IPM. Without counting pests, thresholds are meaningless.

A well-known example is soybean aphid management. A widely used threshold is about **250 aphids per plant**, with most plants infested and populations increasing. That threshold is not random. It is designed to allow time for action before economic loss becomes too high.

Common student mistake: confusing visible damage with the correct action point. By the time damage is obvious, the pest population may already be near or above the economic injury level.

> **Test Tip:** If an APES question asks you to justify delaying pesticide use, mention monitoring and thresholds. That shows you understand IPM as a decision system, not just a list of techniques.

### Tradeoffs among IPM methods

IPM combines different control methods because no single method is best in every case. The exam may ask you to compare them or evaluate which is most suitable in a scenario.

#### Biological control

Biological control uses living organisms or biological agents to reduce pests. Examples include ladybugs eating aphids, parasitic wasps attacking insect pests, or microorganisms such as **Bt** used against certain larvae.

Advantages:

- often more target-specific than broad-spectrum pesticides
- reduces chemical use
- can preserve ecological balance function
- may support long-term pest suppression

Limitations:

- can work slowly
- may depend on weather, habitat, or timing
- may not stop a severe outbreak quickly enough
- introduced control organisms can have unintended effects if poorly managed

Biological control fits IPM well, but it is not always rapid enough for emergencies.

#### Cultural control

Cultural controls change farming practices to make pest outbreaks less likely. Examples include crop rotation, sanitation, resistant crop varieties, intercropping, polyculture, altered planting times, and mulch.

Advantages:

- preventive rather than reactive
- low pollution risk
- can improve soil health and biodiversity
- can disrupt pest life cycles before outbreaks occur

Limitations:

- requires planning
- may not fix a current severe infestation quickly
- may be less convenient for farms built around monoculture
- can involve tradeoffs with mechanization or short-term yield goals

Crop rotation is a good example. If one pest depends on the same host crop year after year, rotating crops can break its life cycle. But a farm heavily specialized in one cash crop may find rotation harder to adopt.

#### Mechanical or physical control

This includes traps, barriers, tillage, hand removal, vacuums, and exclusion methods.

Advantages:

- often immediate
- usually avoids chemical contamination
- can be targeted
- often compatible with beneficial organisms

Limitations:

- labor-intensive
- may be expensive on large farms
- may need repeated use
- often less practical over huge acreages

Mechanical controls are often strong on precision but weak on scale.

#### Chemical control

IPM does not ban pesticides. It places them later in the sequence and uses them selectively when justified by thresholds.

Advantages:

- often the fastest method
- can be effective during serious outbreaks
- scalable on large farms
- useful when other methods are insufficient

Limitations:

- resistance risk
- non-target effects
- runoff and pollution
- possible harm to pollinators, predators, and humans

Within IPM, selective pesticides are usually preferred over broad-spectrum ones because they reduce collateral damage.

A key tradeoff AP students should be able to state clearly:

- chemical control is often strongest for short-term speed
- nonchemical controls are often stronger for long-term sustainability

### A worked APES-style scenario

Imagine aphids are found in a soybean field.

A pesticide-only approach might be:

- detect aphids
- spray immediately with a broad-spectrum insecticide

This may reduce aphids quickly. But it may also kill ladybugs and parasitic wasps, increase resistance pressure, and leave the field more vulnerable to future outbreaks.

An IPM approach would be:

1. identify the pest correctly as aphids
2. scout multiple parts of the field
3. estimate infestation level
4. compare results to threshold
5. check for natural enemies already present
6. use least-harmful effective controls first
7. apply a targeted pesticide only if threshold is exceeded
8. evaluate results and keep records

Suppose scouting shows aphid levels below threshold and strong ladybug presence. Then immediate spraying is probably not the best decision.

Why?

- cost of treatment may exceed expected benefit
- beneficial predators are already providing control
- unnecessary spraying may remove those predators
- removal of predators can trigger pest resurgence or secondary outbreaks

That chain of reasoning is exactly the kind of explanation APES rewards.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Integrated pest management combines multiple control methods and uses pesticides as a later option
- IPM aims to keep pest populations below damaging levels, not eliminate every pest
- Routine pesticide use can harm non-target organisms and increase pollution
- Repeated use of one pesticide can select for resistant pests through natural selection
- The pesticide treadmill happens when resistance leads to heavier or repeated pesticide use
- Monitoring or scouting is essential because IPM decisions depend on actual pest levels
- The economic threshold is the action point before the pest population reaches the economic injury level
- The economic injury level is the lowest pest density where economic damage equals control cost
- Biological, cultural, mechanical, and chemical controls each have benefits and drawbacks
- Broad-spectrum pesticides can kill beneficial predators and pollinators as well as pests
- IPM often lowers long-term environmental and resistance costs but requires more labor, knowledge, and planning
- APES questions on IPM usually reward balanced tradeoff analysis rather than one-sided claims

## Key Terms and Concepts

- integrated pest management (IPM)
- pesticide resistance
- pesticide treadmill
- monitoring (scouting)
- economic threshold (ET)
- economic injury level (EIL)


Integrated Pest Management - IPM tradeoffs