Just Spray ‘Em!?

Based upon the IPM for Teachers Curriculum:IPM Tactic
Adapted by Rachel Hughes and Kirstin Bittel

Time: 1 class period
Materials: Paper and pencil
4 pesticide labels/group including one that claims to be environmentally safe.
Student data tables


After defining what a ‘pest’ is in ‘When Is the Pest’ students will consider what they are doing when they reach for the spray bottle to commit insecticide. Students look at the labels and decipher what they are actually spraying into the air, onto their floors and into their gardens. How the insecticide act on the insect and its toxicity is considered. Impact of insecticide use beyond the death of a pest is considered.

Students will be able to:-
1. Read the label of an insecticide and identify pertinent information including, whether it is a narrow or broad spectrum insecticide, what active chemical is contained and what level of toxicity is displayed.
2. tell that the higher the LD50 the less toxic the chemical
3. Begin to extrapolate the impact of pesticide use beyond the death of the insect

National Science Education Standards
Content Area C- The Interdependence of Organisms
Human beings live within the worlds ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening global stability, and if not addressed, ecosystems will be irreversibly affected.

Resource Websites




Yesterday’s homework asked students to assess the state of pest control in their lives by opening up the yellow pages to ‘Pest Control’, looking in their cupboards for pesticides and asking their families for their input.

1. Today ask students what they found out about pest control in their homes. Are pesticides everywhere?

2. On the board or overhead share with students the following statement: “The US uses over a billion pounds of pesticide-active ingredients each year. Homeowners apply at least 76 million pounds of these insecticides.” Ask students how many pounds of pesticides is that per person? What happens to all these chemicals? Throughout the class they should consider that question, “Where do all the pesticides go?”

3. Pass out copies of different insecticide labels to each group. Ask them what they can tell you about this insecticide based on the label. Students should take notes as they identify qualities of the insecticide including definitions.

4. Start by asking how the insecticide gets into the insect? From the labels students should be able to identify that there are 4 basic “routes of entry” of the poison:

  • Stomach poison (insect must eat it)
  • Contact poison (just has to hit them)
  • Systemic poison (absorbed by the plant and then eaten by insect)
    Fumigant (kills by “breathing” or vapors absorbed across membranes

5. Does this insecticide kill just one specific insect? What other organisms does it affect? Is it a broad or narrow spectrum insecticide? Students should note that a narrow spectrum insecticide might just attack one type of insect; a broad spectrum may have affect lots of different animals.

6. Have students find the active ingredient (a.i.) in the insecticide. Explain that before they can be sold, specific quantities of the active ingredient is fed to mammals, specifically rats, to see how much will kill of 50% of the experimental population. This amount of the active ingredient is known as the Lethal Dose at which 50% of animals die, abbreviated to LD50. Ask students, ‘Why do they test the active ingredient on rats and not on insects?” Rats are used instead of insects as a way to estimate the impact on humans. This assumes a rat’s physiology is similar to a human’s. Let students know that while the LD50 might not be written on the label they are reflected by the use of “signal words” that show increasing levels of toxicity:

Caution <Warning< Danger

7. While the LD50 represents what happens if the rats eat the active ingredient at one time, what would happen if they kept ingesting it at lower levels for longer periods?

8. Students should identify what is the formulation of the insecticide. Explain that insecticides come in different forms and those different forms might have different toxicities dependent on the toxicity of the chemical and how likely you are to be exposed. Ask students what form their pesticide is in. After listing the different forms have students reason which is most toxic of these.

enclosed bait —>granular —>dust —>water solution —>water emulsion
oil solution —>aerosol —>emulsifiable concentrate —>liquid concentrate

Toxicity of a formulation is related to how easily a dangerous amount might be able to get into your system. Liquid concentrates, if swallowed or contacting skin, are more toxic than a dilute or premixed version of the same chemical. Oils "soak" into the skin more. Fine particles of aerosol formulations can pass through the lungs into the bloodstream. Dusts can be breathed if you are not careful but they usually carry relatively little active ingredient. There are, of course, exceptions!

Risk to humans of pesticide use is often described as:
The simplest way to safely use pesticides is read the label, be sure you understand the label and follow ALL instructions

9. Students share within their group information about their pesticide. What is it used for, how strong is it, what might it best be used for.

Students are presented with this scenario:
” Your dad is insisting on buying a pesticide at the store to get rid of the caterpillars that are infesting his citrus plant. You’re not particularly happy about this, since the tree has yet to produce oranges that can be eaten, you’re concerned. What type of pesticide would you use? This can be an imaginary pesticide or an actual pesticide that you have a label for. Justify your reasons.
Let students discuss as a group which they would choose and present to the class. Do they have other suggestions other than use of a pesticide? The following questions can help students get started:

  • Will these products actually control the pest I have? (Am I sure I know what the pest is??! Do I know its life cycle?)
  • Efficacy; short or long term control?
  • What are the active ingredients?
  • What are the relative acute toxicities to humans by signal word? By actual LD50s?
  • What are the risks of exposure due to formulation?
  • What precautions do the labels tell you? How, exactly, would you apply the products safely?

Now that the students know a little more about pesticides have them begin to answer the initial question, “Where do these chemicals go after they are sprayed, ingested or poured into the environment to contact insects?” Students pick one target insect and a pesticide and draw out at least one possible route for the chemicals to travel into the environment. Encourage diverse thinking by questioning students as they draw different routes. Did they consider decomposition of the insect? Where does the chemical go then? Is it still active?

Embedded Assessment
The justifications provided during the scenario provide insight into students’ ability to apply their understanding of the different pesticides.

PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

1996-2007, The University of Arizona
Last update: November 10, 2009
  Page Content: Rachel Hughes
Web Master: Travis Biazo