BioWiki / Pests

Spider mites

tags: - public-ready - export-bio

Spider mites

Overview

Spider mites thrive in hot, dry conditions and can crash crops quickly if missed early.

Symptoms

  • Leaf stippling / bronzing
  • Webbing (later)
  • Hot spots on stressed plants

Conditions that increase risk

Biological control options

IPM notes

  • Focus on early detection + rapid response

Further guidance

  • Spider Mites — Biocontrol Foundations

Key natural enemies

Environmental drivers

  • Strongly favoured by hot, dry conditions and plant water stress.
  • Populations can explode in summer/high radiation periods; damage escalates quickly once webbing begins.
  • Dusty conditions and disrupted predator activity can worsen outbreaks.

Predator–Pest Ratio Example (Spider Mite)

Typical field observations:

  • 1 Phytoseiulus per 5 spider mites → suppression phase
  • 1 per 10–15 → lag risk
  • 1 per 20+ → likely acceleration

Temperature modifier:

  • At 18°C → slower growth
  • At 25–30°C → explosive reproduction

Hot weather reduces margin of safety.

Interpret ratios with: - Predator–Pest Ratio Modelling - Hot Dry Weather - Intervention Decision Logic — Act Or Hold

Thermal Overlap Example — Spider Mite × Phytoseiulus

Spider Mite (Conceptual)

  • Accelerates above ~25°C
  • Explosive reproduction 28–32°C
  • Favoured by dry conditions

Phytoseiulus (Conceptual)

  • Performs well in warmth
  • Requires moderate humidity
  • Efficiency declines in extreme heat + dryness

Overlap Analysis

Moderate warmth (20–26°C): Strong suppression possible.

Hot, dry period (28–32°C): - Pest acceleration increases sharply. - Predator efficiency may plateau or decline. - Rp − Rd gap widens.

Risk increases even if ratios initially acceptable.

Practical Implication

During forecast heatwaves:

  • Shorten monitoring interval
  • Reinforce predator populations early
  • Consider humidity management
  • Avoid disruptive sprays

See: - Thermal Overlap Risk Model - Temperature Driven Pest Acceleration Modelling

Risk Index Scoring (Spider mite)

For consistent scoring and decisions see: - Spider Mite — Risk Index Calibration (V1)

Key anchors: - Heat + dry spell compresses generations → score Thermal Acceleration higher. - Webbing + spread beyond hotspots usually means Pest Trend ≥ 3. - Predator ratios must be interpreted with distribution (coverage) and heat stress.

Related: - Hot Dry Weather - Thermal Overlap Risk Model - Predator–Pest Ratio Modelling

IPM Risk Engine Integration

Spider mites are classified in the IPM Risk Engine as:

Dry Heat Amplifiers

See: - Ipm Risk Engine Hub - Ipm Risk Engine — Protected Crops

Risk escalates under sustained temperature rise and canopy RH suppression.