How does a spider mite survive the winter in a greenhouse? - briefly
Spider mites overwinter in greenhouses by sheltering in protected microhabitats such as leaf folds, plant debris, and the humid zones near heating equipment, where they can remain active at low temperatures or enter diapause. Their capacity to reproduce slowly on evergreen hosts maintains the population until conditions improve.
How does a spider mite survive the winter in a greenhouse? - in detail
Spider mites persist through colder months in greenhouse settings by exploiting several physiological and behavioral adaptations. Adult females deposit eggs that enter a diapause state when temperatures fall below about 10 °C. Diapausing eggs possess thickened chorions, reducing water loss and allowing them to remain viable for several weeks despite low humidity.
Once laid, eggs are positioned in micro‑habitats that buffer environmental fluctuations. Common refuges include leaf axils, trichome clusters, undersides of leaves, and crevices of plant stems. These locations retain slightly higher temperatures and humidity than the surrounding air, creating a microclimate that slows development without triggering mortality.
Metabolic activity of both eggs and dormant stages declines sharply as ambient temperature drops. Enzyme systems adjust to function at lower temperatures, and cellular membranes incorporate more unsaturated fatty acids, preserving fluidity. This metabolic suppression conserves energy reserves until conditions become favorable for hatching.
Greenhouse climate control inadvertently supports overwintering. Heating systems often maintain nighttime temperatures above the lethal threshold for spider mites, while ventilation may create temperature gradients that allow mites to migrate to warmer zones. Humidity regulation, especially when dew points are kept low, reduces fungal competition, indirectly favoring mite survival.
Biological factors also contribute. Populations of predatory mites are reduced by cold, decreasing predation pressure on spider mite eggs. The resulting predator‑prey imbalance permits a higher proportion of mite eggs to survive diapause.
Key mechanisms can be summarized:
- Diapause induction – triggered by temperature ≤ 10 °C, short photoperiod.
- Protective oviposition sites – leaf undersides, trichomes, stem cracks.
- Physiological adjustments – membrane lipid remodeling, enzyme activity modulation.
- Microclimate exploitation – migration to heated zones, use of greenhouse humidity control.
- Reduced natural enemies – cold suppresses predatory mite activity.
Effective greenhouse management to disrupt these strategies includes lowering night temperatures below the diapause threshold, increasing ventilation to create uniform cooling, removing plant debris that shelters eggs, and introducing cold‑tolerant predatory mite strains before winter. By targeting each survival component, growers can diminish overwintering populations and reduce subsequent infestations.