Biological pest control – natural enemies versus chemical pesticides
BiologyEcology & EnvironmentAges 17–18
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Ecology & Environment
Simulate one rice-growing season with a brown planthopper population and its natural enemies (mirid bugs, spiders). Choose a strategy: no intervention, scheduled spraying, releasing natural enemies, or integrated pest management (IPM) that sprays only above the economic threshold. Track pest density against the threshold, natural enemies killed alongside the pests, pest resurgence and resistance, and the season's final yield and cost.
Lesson: Biological control
What it shows
Pest numbers are regulated by natural enemies as well as by pesticides. The simulation models a rice crop over one season, with brown planthoppers and predators such as mirid bugs and spiders linked by predator–prey dynamics. Routine broad-spectrum spraying kills predators along with pests, so the pest resurges quickly and each spray selects for resistance. Biological control uses natural enemies to hold the pest below the economic threshold, the density at which damage would cost more than control. Integrated pest management (IPM) combines natural enemies with spraying only when that threshold is exceeded.
How to use
Start with No intervention to see how far the planthopper population climbs above the threshold line. Switch the Strategy to Scheduled spraying and change the Scheduled spray interval, noting how the pest resurges after each spray. Try Release natural enemies with different numbers of Natural enemies released, and finally IPM – spray above threshold. Use the table to compare sprays, pest peak, yield, cost and profit across all four strategies.
Parameters you can change
- Strategy No intervention, Scheduled spraying, Release natural enemies, IPM – spray above threshold
- Natural enemies released 0–20 individuals/m²
- Scheduled spray interval 5–30 days
Questions to explore
- Why does frequent scheduled spraying lead to higher pest peaks later in the season?
- What is the economic threshold, and how does IPM use it to decide when to spray?
- Why do natural enemies keep the planthoppers below the threshold without eliminating them completely?
