Lesson Plan: Lures and Traps

Objectives

• To demonstrate how traps work to monitor and/or control pests
• To exhibit how lures can increase the effectiveness of traps
• To illustrate how lures can be coupled with repellents to move pests
• To show how pheromone lures can disrupt pest reproduction
• To show how the sterile insect technique can disrupt pest reproduction

Introduction

Insect pests all have at least one life stage in which they move from one place to another to find essential resources. For example, they might move to find a new food source, shelter, or mates. Traps and lures may intercept or redirect the pests during that movement, which can be used to aid in their management.

Some insect traps, such as pitfall traps and fly tape, capture insects that walk or fly into the trap by chance. These traps usually do not capture enough pests to reduce their damage, but they can be used to confirm which species of pest is present and give an estimate of its abundance. That information, combined with information about the pest, can be used to determine if a treatment is needed and which treatment is most appropriate.

Other traps include lures that can draw large numbers of pests into the trap. The type of attractant can vary depending on the type of pest. Ultraviolet lights, different colors, foods, and synthetic pheromones (chemicals that insects use to communicate through smell) have all been used as lures. Because a lure can make pests actively approach a trap, traps with lures often catch far more pests than traps without lures, to the point that they may be used to trap a significant portion of the pest population.

Lures can also be used without traps to move pests to areas where they do not cause problems. For example, a lure may be used to make pests leave a crop field, where they were damaging the crop, and settle into the field edges, where they do not harm anything. Combining lures in the area where you want the pests to go with repellents in the area that you want pests to leave can be even more effective at driving pests out. This strategy is often called the push-pull strategy.

For many insects, reproduction is the phase of life that is easiest to manipulate with lures. In some cases, insects use sex pheromones to find mates. Usually, one sex sits still and releases the sex pheromone while the other sex follows the pheromone trails to pair up. A trap coupled with a concentrated sex pheromone lure can capture most or all of the searching sex, leaving the sitting sex without mates and unable to reproduce. This strategy is called mating disruption.

An alternative way to disrupt insect reproduction is called the sterile insect technique. This technique is used against species in which the female mates only once, and some method is available to sterilize males without compromising their ability to attract and mate with females. Massive numbers of males are raised in a lab, sterilized, then released into the wild. Because the sterilized males far outnumber the wild males, females are more likely to mate with sterilized males than with fertile males, leading to no fertilized eggs and no reproduction. In sterile insect technique, each sterile male functions similarly to a lure. Each "lure" is equally attractive to its naturally occurring counterparts, but they are deployed in massive quantities. This strategy has been used most famously to eradicate the New World primary screwworm fly, a major pest of livestock, wildlife, and public health, from the continental United States.

Activity Procedures

This lesson plan will include 5 activities that will demonstrate how different trap and lure strategies work. Participants should be familiar with the introduction before doing the activities. Perform the steps of each activity in order so that results are not biased by participants knowing too much about the activity before it begins.

Trap Demonstration

1. Gather the materials:
   1. Cardboard-backed pest glue traps or strong tape
   2. Mixed seed bird seed (identify one seed, such as millet, that will represent pests; all other seeds represent non-pest insects)
   3. A 10 ft. x 10 ft. open section of floor or ground to use as a sampling arena
   4. Some sort of marker to delineate the sampling arena, if it is not naturally defined (e.g., sidewalk chalk, tape, marking flags, etc.)
   5. A pen and notebook or calculator
   6. A 10 ft. x 10 ft. or larger tarp to contain the activity
   7. A broom and dustpan for cleanup
   8. Step 4 clarifies what each item represents.
2. Set up the demonstration:
   1. Spread the tarp on the ground to serve as the arena.
   2. Place 3 glue traps or 6-inch tape strips (adhesive side up) in the arena. Spread them out, but the exact arrangement does not matter.
   3. Give each participant one tablespoon of bird seed
3. Have each participant toss their bird seed into the arena so that it scatters around the arena. They can choose how they toss the seed; a high arch, a hard line-drive throw, etc.
4. Explain what each item represents:
   1. The arena is an area where pests live or move.
   2. The glue traps or tape are insect traps without lures.
   3. The millet in the bird seed represents pests.
   4. Any other seeds in the bird seed mix are other insects that are not pests.
5. Distribute the glue traps or tape strips to three participants. Have them count how many millet seeds and other seeds are stuck to the traps.
6. Record the number of caught seeds and use the calculator or notebook and pencil to calculate an average per trap for millet seeds and other seeds.
7. Discuss the results:
   1. Did the traps attract the seed, or simply catch seed that happened to touch them?
   2. If you knew seeds well, would you be able to identify which seeds are in the area by what was caught by the trap?
   3. Did the traps catch a large portion of the pests, or only a small portion of them?
   4. Do you think the number of trapped pests is correlated with the total number of pests (e.g., if the total number of pests goes up, then the number of trapped pests will increase proportionally)?
   5. Do you think you could catch a more significant number of pests if you place more traps?
      1. Discuss practical limitations to using enough traps to eliminate the pests (e.g., cost of traps, covering the whole ground in traps, time/labor of dealing with traps, capture of too many non-pest insects, etc.)
   6. If time allows, repeat the exercise to test 7d and 7e
      1. To test 7d, repeat the exercise but have each participant throw 3 tablespoons of bird seed into the arena instead of only one. See if the number of trapped pest seeds is about 3 times that of the first iteration.
      2. To test 7e, repeat the exercise but place 9 traps instead of 3. See if the total number of trapped pest seeds is about 3 times that of the first iteration.

Trap and Lure Demonstration

1. Gather the materials:
   1. A large table
   2. A large blanket, towel, or tablecloth
   3. Small, individually-wrapped, uniform candies (e.g., Hershey kisses, Jolly Ranchers of all one flavor, etc.): at least 3 candies per participant
   4. A permanent marker
   5. A bowl or plate
   6. Step 5 clarifies what each item represents.
2. Set up the demonstration:
   1. Place the table
   2. Place the blanket, towel, or tablecloth on the table. Ensure it is ruffled and crumpled, not smooth.
   3. Mark the wrappers of half of the candy with the permanent marker; leave the other half unmarked.
   4. Scatter the marked candies on the blanket, towel, or tablecloth. Re-shuffle the blanket so that the candies have a chance of being partially or fully covered by folds or creases.
   5. Place all of the unmarked candies in the bowl, and place the bowl in the middle of the table.
3. Invite all participants to come to the table and take one piece of candy. Be careful not to draw extra attention to the marked candy on the table or the unmarked candy in the bowl.
4. Ask all participants to check whether their candy has a mark on the wrapper or is unmarked.
5. Explain what each item in this activity represents:
   1. The table represents the pest’s foraging area.
   2. The candy represents an attractant. The marked candy represents natural attractants (e.g., food or mates) while the unmarked candy represents a lure.
   3. The bowl represents the trap that contains the lure.
   4. Each participant represents a pest.
      1. Each participant with an unmarked piece of candy represents a pest that entered a trap for a lure and was captured or killed.
      2. Each participant with a marked piece of candy represents a pest that found natural resources rather than entering the trap for the lure.
   5. Ask each participant who was a pest in the trap (i.e., had unmarked candy) to raise their hands. Make a note of the proportion of participants who entered the trap.
   6. Discuss the results. Participants may eat their candy during the discussion.
      1. Ask the participants if they thought that a greater proportion of pests get trapped if the trap includes a conspicuous lure (like a candy bowl) than if the trap depends on random chance, like in the first activity.
      2. Discuss some of the factors that might affect the effectiveness of the lure:
         1. The amount of natural attractants competing with the lure
         2. The ease of finding natural attractants competing with the lure
         3. The attractiveness of the lure
         4. The number of lures relative to the size of the space

Push-Pull Demonstration

1. Gather the materials:
   1. An air horn
   2. A large enough arena that all participants can enter and walk freely
   3. Some sort of markers (tape, sidewalk chalk, marking flags, etc.) to identify the boundary of the arena and divide it into two equal-sized halves.
   4. Two types of individually wrapped candy. The candy should be the same in every way except size (e.g., all peanut butter cups, with half small and half full-size). Each participant should have at least one candy of each size.
   5. Step 5 clarifies what each item represents.
2. Set up the activity:
   1. Mark the boundaries of the arena and include a line cutting the arena in half so there are two equally-sized, adjacent arenas.
   2. Scatter the small candies on one side of the arena and the large candies on the other side of the arena.
3. Explain the rules of the activity to the participants:
   1. One participant at a time should enter the arena.
   2. After entering the arena, go to one piece of candy and pick it up. Do not move after you have your piece of candy.
4. Invite a participant to enter the arena and find their piece of candy.
   1. For every step that a participant takes on the small candy side of the arena, blast the air horn. Do not use the air horn when participants are on the large candy side of the arena.
   2. After a participant finds their candy and stops moving, invite the next participant to repeat the exercise. Continue until all participants have a piece of candy.
5. Explain what each item represents:
   1. The arena represents a pest's foraging area.
      1. The small candy side represents a farm field where the pest would cause damage
      2. The large candy side represents a field edge where the pest would not cause damage
   2. The small candy represents the crop that the pest would eat.
   3. The large candy represents a lure.
   4. The air horn represents a repellent.
6. Discuss the results. Participants may eat their candy during the discussion.
   1. Which side of the arena did most participants end up on: the field with crops and a repellent (small candy side with air horn), or the field edge with lures (large candy side without air horn)?
   2. Do you think the use of lures (large candy outside the crop) and repellents (the air horn) caused less damage than if neither was used (i.e., there is no large candy and there is no air horn)?

Mating Disruption Demonstration

1. Gather the materials:
   1. An arena space that is about 10 feet by 10 feet
   2. A blindfold
   3. 10 paper clips
   4. 4 small binder clips
   5. 20 pieces of ribbon, paper streamers, or strips of toilet paper, each about 3 feet long
   6. 40 pieces of ribbon, paper streamers, or strips of toilet paper, each about 6 feet long
      1. The size of the arena and number and size of pieces of ribbon, paper streamers, or strips of toilet paper can be scaled up or down, but two-thirds of the pieces should be 2-4X as long as the remaining third.
   7. Step 3 clarifies what each item represents.
2. Set up the activity
   1. Use each paper clip to connect two of the 3-foot-long pieces of ribbon, paper streamers, or strips of toilet paper in a V shape
      1. If the exercise is scaled down, use one-tenth of the short pieces in each paper clip
   2. Use each binder clip to connect 10 of the 6-foot-long pieces of ribbon, paper streamers, or strips of toilet paper in a fan or V shape
      1. If the exercise is scaled down, use one-fourth of the long pieces in each binder clip
   3. Spread all 10 paper clip setups throughout the arena, with each V oriented the same way.
   4. Spread all 4 binder clip setups throughout the arena, with each V oriented the same way and consistent with the paper clip Vs.
3. Explain what each item represents:
   1. Each participant is an insect searching for the scent plume of a mate.
   2. Each paper clip is a potential mate
   3. Each binder clip is a lure in a trap
   4. The ribbon, streamer, or toilet paper is a scent plume
      1. Ask all participants to reflect on how smell works. It moves through the air with the wind, but you can only detect the presence/absence of the smell and the intensity of the smell, not exactly where it comes from. Knowing that it moves with the wind, if you notice a smell that you want to follow, you should be able to head upwind to find the source of the smell. If you accidentally wander out of the scent plume, you can start going back and forth across the wind until you find it again. Smoke from a campfire is visible and behaves similarly to an odor plume, except smoke rises because it is hot while an odor plume does not rise.
         1. The blindfold will be used to simulate the ability to detect presence/absence of what is immediately around you without knowing what is farther away. Participants are using their sense of touch (feeling for ribbon or paper) rather than smell.
         2. The clip at the point of each V is the source of the scent at the upwind end of the scent plume. As the scent moves downwind, it spreads, which is why each plume is V-shaped or fan-shaped.
      2. Explain the rules of the activity:
         1. Participants will take turns, going one at a time.
         2. On a participant’s turn, they will put on the blindfold.
         3. While blindfolded, the facilitator will guide them to the side of the arena with the open ends of each V
         4. The participant will then crouch down and start moving through the arena while feeling for the ribbon or paper on the floor. When they find one, they should follow it by touch to its point.
         5. When they get to a point, the participant can remove the blindfold and determine if they arrived at a paper clip or at a binder clip. Ask them to remember which type of clip they got. Do not remove the clip or the V from the arena.
         6. Continue until all participants have taken a turn.
      3. Discuss the results:
         1. Ask the participants who got paper clips to raise their hands. Make a note of the proportion of participants who got paper clips.
         2. Remind everyone that those who got paper clips successfully found mates, while those who got binder clips were trapped at a lure.
         3. Ask the participants why they think the lures had so much larger scent plumes than the insects did.
            1. Answer – since lures have synthetic sex pheromones, the manufacturer can put a large amount of pheromone in the lure. Real insects have to put metabolic energy into producing and releasing the pheromone. In addition, natural enemies can track down insects by following their odor plumes. So, real insects must balance mate attraction with the natural drawbacks of producing a large odor plume.
         4. Discuss how many participants found a mate and reproduced successfully, compared to how many were trapped at the lure.
            1. How do you think those numbers would change if the lures were not in the arena?
         5. Do you think it matters if the participants are males and the paper clips are females or vice versa?

Sterile Insect Technique Demonstration

1. Gather the materials:
   1. 100 beads of one color
   2. 10 beads of a different color
   3. An opaque bag or jar to hold the beads.
   4. Step 4 clarifies what each item represents.
2. Set up the activity:
   1. Place all of the beads in the bag or jar
3. Have one participant at a time pull a bead out of the bag or jar by touch. Have them keep their bead until the end.
4. Explain what each item represents:
   1. Each participant represents a female insect seeking a mate
   2. Each bead represents a male insect
      1. The 100 beads represent released sterile males.
      2. The 10 beads represent wild fertile males
   3. Discuss the results:
      1. If you, as a mate-seeking female insect, got a released sterile male, would you reproduce successfully? What if you got a wild fertile male?
      2. What proportion of participants drew wild fertile males and reproduced successfully?
      3. If only a small proportion of females reproduced successfully and the same number of sterile males are released in the next generation, do you think the females in the next generation have better or worse odds at getting a wild fertile male?
      4. What biological factors are required for this system to work (either in terms of this exercise or in biological terms)?
         1. Females only take one bead / females mate only one time.
         2. The beads are indistinguishable until you have committed to one / females cannot distinguish between wild fertile males and released sterile males.
         3. The sterile male beads far outnumber the fertile male beads / the released sterile males far outnumber the wild fertile males