Biological Control in Hydroponic Systems:
Beneficial Insect Application and Management
This article is the fourth part of a series on integrated pest management in hydroponic systems.
1. Basic Principles of Biological Control
Definition of Biological Control
Biological control refers to the targeted use of natural antagonists (predators, parasitoids, pathogens) to regulate pest organisms. In hydroponic systems, this approach offers particular advantages due to the controlled environmental conditions (van Lenteren, 2012).
Conservative Control
Promotion of existing beneficial insect populations through habitat design and reduction of disturbing factors.
Sustainable Cost-effective
Augmentative Control
Repeated release of beneficial insects to strengthen natural populations or when they are absent.
Cost-intensive Precise
Inoculative Control
One-time release with the aim of permanent establishment of a self-sustaining population.
Long-term Self-sufficient
2. Spectrum of Beneficial Insects for Hydroponics
| Beneficial Insect | Taxonomy | Target Pests | Predation Rate/Parasitism | Optimal Conditions |
|---|---|---|---|---|
| Phytoseiulus persimilis (Predatory mite) |
Arachnida: Phytoseiidae | Spider mites (Tetranychus spp.) | 5-20 eggs/larvae/day or 5 adults/day |
20-28°C, 60-80% RH |
| Amblyseius swirskii (Predatory mite) |
Arachnida: Phytoseiidae | Thrips, Whiteflies | 1-3 thrips larvae/day + 5-15 whitefly eggs |
22-30°C, 70-85% RH |
| Encarsia formosa (Parasitic wasp) |
Hymenoptera: Aphelinidae | Whiteflies (Trialeurodes) | 50-100 parasitizations/wasp/lifetime | 20-26°C, 50-80% RH |
| Orius laevigatus (Flower bug) |
Hemiptera: Anthocoridae | Thrips, Aphids, Spider mites | 10-15 thrips/day (nymph and adult) |
20-30°C, 60-80% RH |
| Aphidius colemani (Parasitic wasp) |
Hymenoptera: Braconidae | Green peach aphid | 200-300 parasitizations/wasp | 18-25°C, 60-75% RH |
| Cryptolaemus montrouzieri (Ladybug) |
Coleoptera: Coccinellidae | Mealybugs, Aphids | 100-200 mealybugs/larva | 20-28°C, 70-80% RH |
Banker Plant Systems
Principle: Use of alternative host plants for continuous beneficial insect production directly within the system.
Examples:
- Cereal aphids on wheat for Aphidius species
- Meal moth eggs for Trichogramma parasitic wasps
- Artemia cysts as substitute prey for predatory mites
Source: Huang et al., 2011
Microbial Antagonists
Principle: Use of pathogenic microorganisms against insect pests.
Important Species:
- Beauveria bassiana: Fungus against whiteflies, thrips
- Metarhizium anisopliae: Fungus against soil larvae
- Bacillus thuringiensis: Bacterium against lepidopteran larvae
- Verticillium lecanii: Fungus against aphids, whiteflies
3. Application Techniques and Establishment
Delivery Forms and Handling
| Delivery Form | Advantages | Disadvantages | Suitability for Hydroponics |
|---|---|---|---|
| Carrier material (Vermiculite, Bran) |
Easy application | Limited shelf life | High |
| Blister packs (Slow-Release) |
Controlled release | Higher costs | Very high |
| Spray applications (Fungal spores) |
Large-area distribution | Environmentally sensitive | Medium |
| Brevicapsules (Beneficials in capsules) |
Precise placement | Complex application | Good |
Application Strategies
Inundative Release
High release densities for rapid pest control:
- Phytoseiulus persimilis: 25-50/m² at the onset of infestation
- Encarsia formosa: 1 wasp/2m² weekly
- Orius laevigatus: 1-2/m² every 2 weeks
Inoculative Release
Lower densities for establishment:
- Amblyseius swirskii: 10-25/m² preventively
- Aphidius colemani: 0.25-0.5/m² at first aphids
Placement Strategies in Hydroponic Systems
NFT Systems
- Vertical distribution: Every 2-3 meters at plant mid-height
- Channel inlets: Beneficials migrate with nutrient film
- Plant-based application: Directly onto leaves
DFT Systems
- Floating islands: For flying beneficials
- Edge areas: Dry zones for soil arthropods
- Plant supports: Use as migration paths
Vertical Farming
- Tiered application: Separately for each level
- Ventilation systems: For distribution of flying species
- Monitoring per level: Different conditions
4. Optimal Rearing Conditions
| Beneficial Insect | Temp. Optimum (°C) | RH Optimum (%) | Light Requirement | Development Time | Special Requirements |
|---|---|---|---|---|---|
| P. persimilis | 20-28°C | 60-80% | > 12h | 7-10 days | High spider mite density |
| A. swirskii | 22-30°C | 70-85% | > 10h | 10-12 days | Pollen as supplementary food |
| E. formosa | 20-26°C | 50-80% | > 14h | 14-20 days | Direct contact with hosts |
| O. laevigatus | 20-30°C | 60-80% | > 12h | 20-25 days | Flowers for adult nutrition |
| A. colemani | 18-25°C | 60-75% | > 10h | 10-15 days | Consider host specificity |
Critical Factors: Temperature fluctuations >5°C/day and humidity <50% can significantly reduce the effectiveness of beneficial insects. Continuous climate monitoring is essential.
5. Monitoring and Population Control
Quantitative Assessment Methods
Direct Counting Methods
- Leaf samples: 10-20 leaves/parcel
- Tap samples: Over white surface
- Visual inspection: Systematic assessments
Indirect Methods
- Sticky traps: For flying stages
- Pheromone traps: Species-specific
- Damage assessments: Feeding traces, discolorations
Thresholds and Decision Making
| Pest Organism | Intervention Threshold | Beneficial Ratio | Action Recommendation |
|---|---|---|---|
| Spider mites | 2-5 mites/leaf | 1:5 (Predator:Prey) | Release P. persimilis |
| Whitefly | 1 adult/10 plants | 1:50 (Parasitoid:Host) | Establish E. formosa |
| Thrips | 1-2 thrips/yellow trap/day | 1:10 (Predator:Prey) | A. swirskii + O. laevigatus |
6. Combination with other IPM Measures
Integrative Strategies
Compatible Plant Protection Products
- Selective insecticides: Spinosad, Azadirachtin
- Microbial preparations: B. thuringiensis
- Plant strengtheners: Silicates, Chitosan
- Repellents: Essential oils, Diatomaceous earth
Cultural Measures
- Hygiene: Cleaning, disinfection
- Plant spacing: Optimized air circulation
- Nutrient management: Balanced supply
- Irrigation optimization: Avoidance of stress
Physical Barriers
- Insect screens: 0.3-0.5mm mesh size
- UV-blocking films: Reduces insect flight
- Trap crops: Targeted diversion
- Reflective materials: Confusion effects
References
- van Lenteren, J. C. (2012). The state of commercial augmentative biological control: plenty of natural enemies, but a frustrating lack of uptake. BioControl, 57(1), 1-20.
- Huang, N., Enkegaard, A., Osborne, L. S., Ramakers, P. M., Messelink, G. J., & Pijnakker, J. (2011). The banker plant method in biological control. Critical Reviews in Plant Sciences, 30(3), 259-278.
- Messenger, P. S., & van den Bosch, R. (1.971). The adaptability of introduced biological control agents. In Biological Control (pp. 68-92). Springer, Boston, MA.
- Collier, T., & Van Steenwyk, R. (2004). A critical evaluation of augmentative biological control. Biological Control, 31(2), 245-256.
- Parrella, M. P., & Lewis, E. E. (2017). Integrated pest management in protected culture. In Handbook of Pest Management (pp. 345-372). CRC Press.
Next article in the series: System Hygiene and Prevention: Foundation of Successful Pest Control in Hydroponics
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