Managing the Threat - Soybean Aphids

Managing the Threat - Soybean Aphids

Target Grade Level / Age Range:

High School (9-12)

Estimated Time:

90 minutes

Purpose:

Students will identify pests in agroecosystems – specifically soybean aphids – and determine how to address them and protect the harvest.

Materials:

  • Printed copies of page 28 of Soybean Aphid Field Guide – one per student
  • Printed copy of Soybean leaves aphid count document
  • Tape

Essential Files (maps, charts, pictures, or documents)

Vocabulary (with definitions)

  • Soybean – also called soja bean or soya bean, annual legume of the pea family (Fabaceae) and its edible seed. The soybean is economically the most important bean in the world, providing vegetable protein for millions of people and ingredients for hundreds of chemical products
  • Aphid – small sap-sucking insects and members of the superfamily
  • Economic threshold – In integrated pest management, the economic threshold is the density of a pest at which a control treatment will provide an economic return. An economic threshold is the insect's population level or extent of crop damage at which the value of the crop destroyed exceeds the cost of controlling the pest. Economic thresholds can be expressed in a variety of ways including the number of insects per plant or per square meter, the amount of leaf surface damage, etc.
  • Yield – the amount of a given agricultural product produced
  • Bushel – a measure of capacity equal to 64 US pints (equivalent to 35.2 liters), used for dry goods. A bushel of soybeans weighs 60 pounds
  • Hectare - a metric unit of square measure, equal to 2.471 acres or 10,000 square meters.

Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)

The soybean aphid, Aphis glycines Matsumura, is the only aphid known to extensively colonize soybean fields in North America. This pest is a potential threat to virtually all soybeans grown in the US and Canada. However, some states are more at risk of economic infestations than others. In addition to geographical considerations, soybean fields at highest risk include those planted late and those that experience hot, dry weather that stresses the crop. Because soybean aphid populations can increase rapidly, growers should scout regularly, monitor population levels and be prepared to treat if necessary. Soybean aphids have many natural insect enemies such as lady beetles and their larvae that can help keep moderate populations in check. Fungal diseases are also emerging as important factors in aphid population regulation.

Interest Approach – Engagement (what will you do to engage students at the beginning of the lesson)

 Aphid count on soybeans is used to determine if/when to spray insecticides to control the aphids. Soybean aphids have been a problem since they were first introduced between 2000 and 2004. Play the video Soybean Aphids from AgPhD https://youtu.be/8fGo9OGIl-g. Present slides 2-6 in the PowerPoint – Managing the threat.

Procedures

1.       Graphing the problem: Present students with the following data set from the 2007 paper entitled Economic Threshold for Soybean Aphid:

Cost of control ($/ha)

Market price ($/ton)

Yield Potential (ton/ha)

Cumulative aphid-days

Aphids per plant

16.41

202.09

2.02

5649

684

16.41

202.09

2.69

4188

507

16.41

202.09

3.36

3309

401

16.41

202.09

4.04

2715

329

16.41

220.46

2.02

5160

625

16.41

220.46

2.69

3821

463

16.41

220.46

3.36

3015

366

16.41

220.46

4.04

2471

300

16.41

238.83

2.02

4747

575

16.41

238.83

2.69

3510

425

16.41

238.83

3.36

2766

335

16.41

238.83

4.04

2264

275

  • Ask students to work in pairs to sort and graph the data. They can use graph paper, a graphing calculator, or other graphing software as available (MS Excel or other).
  • Ask students to plot or graph the yield potential. Number of aphids should be across the X axis and tons per hectare should be up the Y axis. A sorted data set might look like:

 

Aphids per plant

Yield Potential (ton/ha)

275

4.04

300

4.04

329

4.04

335

3.36

366

3.36

401

3.36

425

2.69

463

2.69

507

2.69

575

2.02

625

2.02

684

2.02

 

  • A plotted line graph might look like:

  • What can students deduce from the graph? How do aphids affect soybean yield? Are there levels of aphid infestations that cause decreases in yield?
  1.  Diagnosing the problem, identifying the threshold
    1. Play the following scouting video to help students understand the procedure of crop scouting and counting aphids: https://youtu.be/KXg_pOyZeqE OR use slides 7-8 of the Managing the threat PowerPoint.
    2. Prior to class, past the printed soybean leaves (from soybean leaves aphid count.pptx) around the classroom. Pass out copies of the soybean aphid field guide to each student. Explain to students that each leaf that is placed around the room represents a random sample of a much larger field. Each leaf is 30 rows or paces from the next plant.
    3. Have students follow the instructions on the Speed Scouting for Soybean Aphids worksheet to collect their data. Directions for Speed Scouting:
      1. Go to a plant at random and start counting aphids. If less than 40 aphids are on the ENTIRE plant, mark a minus [-] for that non-infested plant. If you reach 40 aphids, STOP COUNTING (this is the speedy part!) and mark a plus [+] for that infested plant.
      2. Walk 30 rows or paces at random to find the next plant. Repeat Step #1 until 11 plants are sampled in different areas of the field. Total the number of infested plants [+] to make a treatment decision.
      3. If you must ‘CONTINUE SAMPLING’ (7-10 plants with a [+]), sample 5 more plants and use the new total number of plants to make a decision.
      4. If no decision is reached, sample additional sets of 5 plants until 31 plants are sampled. Remember, always use the total number of infested plants [+] to make a decision. If no decision can be made after sampling 31 plants, resample the same field in 3-4 days.
      5. A ‘TREAT’ decision must be confirmed a second time 3-4 days later. If confirmed, apply an insecticide in 3-4 days.
    4. After all students have gathered their individual data, bring the class back together and have them discuss whether or not they should treat the field or not. NOTE: Based on data collected, some students may decide that the field should not be treated. But, most students will likely discover that the field should be treated based on their counts. Lead a discussion on how students arrived at different answers. Facilitate a discussion until the group can reach a consensus.
    5. Break students up into three groups. Have each group be responsible for researching one treatment option and then reporting back to the class.
      1. Group 1: Chemical Treatment
        1. Possible resource: https://www.pioneer.com/home/site/us/agronomy/soybean-aphid-management/
        2. What are the spraying considerations?
        3. How do farmers ensure coverage of their field?
        4. When should it be applied? What are the timing considerations?
        5. What safety procedures should farmers follow when applying?
        6. What are the pros and cons of each prospective chemical?
      2. Group 2: Maintaining a balance in the ecosystem by increasing the number of biological controls the aphids.
        1. Possible resource: https://www.pioneer.com/home/site/us/agronomy/soybean-aphid-management/
        2. What are the natural enemies of soybean aphids? Use slide 9 of the PowerPoint – Managing the Threat.
          1. Asian lady beetle (larva and adult)
          2. Green lacewing (larva)
          3. Insidious flower bug (nymph)
          4. Spined soldier bug (nymph)
          5. Parasitoid wasp (adult)
      3. Group 3: How do ecosystems achieve or maintain balance?
        1. Could wild cultivars resistant to aphids be used to genetically engineer new domestic varieties?
          1. Possible resource: https://www.pioneer.com/home/site/us/agronomy/soybean-aphid-management/
          2. Possible resource: https://www.sciencedirect.com/science/article/pii/S2352340917304432
          3. What is soybean antibiosis?
          4. What are aphid resistant cultivars?
    6. After students have completed their research, each group should develop a news report to share their material with the rest of the class. One (or two) students would serve as the reporters and the rest of the students in the group would role play and act as the experts. Reporters ask questions of the experts. Reporters should write down their questions and experts should be prepared to answer them. Have the group practice their news report before presenting to the rest of the class.

Did you know? (Ag facts)

  • As many as 31 states have seen soybean aphids in fields. Eight states around the Great Lakes and upper Midwest are at highest risk for infestation. These include Illinois, Indiana, Iowa, Michigan, New York, Ohio, Pennsylvania, and Wisconsin.
  • Soybean aphids are wingless in their colony-building phase. They later form wings and can migrate.
  • Common soybean aphid natural enemies include: a) multicolor Asian lady beetle, b) green lacewing; c) insidious flower bug, d) spined soldier bug, e) parasitoid wasp.

Extension Activities (how students can carry this beyond the classroom)

  • Have students look at other diseases or insects that can affect crop yield. Have then find datasets that can showcase the yield decline as the disease/insect infestation takes hold.
  • Have students identify treatment options for different diseases/insects.
  • Have students calculate economic return based on current soybean prices. Can the farmer afford the cost of spraying?

Suggested Companion Resources (books and websites)

Sources/Credits

Author(s)

Will Fett

Organization Affiliation (your organization)

Iowa Agriculture Literacy Foundation

Agriculture Literacy Outcomes

  • T1.9-12.c. Discuss the scientific basis for regulating the movement of plants and animals worldwide to control for the spread of potentially harmful organisms (e.g., invasive species and disease-causing organisms such as foot and mouth disease and avian and swine flu) as well as the methods of control in place (state, national, and international policies, economic incentives)
  • T1.9-12.g. Identify non-native or invasive species in your state that impact the sustainability and/or economic value of natural or agricultural ecosystems

Iowa Core Standards

  • HS-LS2-2. Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales.