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Introduction
The two most common whitefly pests found in greenhouse production are greenhouse whitefly (Trialeurodes vaporariorum) and sweetpotato whitefly (Bemisia tabaci). Greenhouse whitefly commonly infests tomatoes, cucumbers, peppers, ornamental plants, and many other greenhouse crops (Photo 1). Sweetpotato whitefly is a highly adaptable species that attacks a wide range of greenhouse crops and can transmit several plant viruses. These tiny, sap-feeding insects reproduce rapidly under warm greenhouse conditions and can quickly develop into serious infestations if left unmanaged. Whiteflies damage plants by feeding on sap, weakening plant growth, causing leaf yellowing, and producing sticky honeydew that promotes the development of sooty mold. Certain whitefly species can also transmit plant viruses, resulting in significant crop losses.
Fortunately, greenhouse growers have effective and environmentally friendly alternatives to conventional insecticides, including biological control agents such as beneficial predatory mites and parasitic wasps. These natural enemies target different stages of the whitefly life cycle and can provide long-term pest suppression when introduced early. They can also be incorporated into an integrated pest management (IPM) program. This article explores the most effective beneficial organisms for managing greenhouse whiteflies, their recommended release rates, and strategies for establishing a successful biological control program.
Damage caused by greenhouse whiteflies
Adult whiteflies are small, white, winged insects commonly found on the undersides of leaves. Females lay eggs on leaf surfaces, and the developing immature stages remain attached to the foliage while feeding. Whiteflies cause direct damage (Photo 2) by sucking plant sap, which reduces plant vigor and can lead to leaf yellowing and premature leaf drop. They also cause indirect damage by secreting honeydew, which promotes the development of sooty mold on plant surfaces (Photo 3). Sooty mold can interfere with photosynthesis by reducing the amount of light reaching the leaf surface. In addition, whiteflies are known to transmit several plant viruses. Both direct and indirect damage can reduce crop quality, marketability, and yield. Because whiteflies reproduce rapidly, early detection and preventive biological control are essential for effective whitefly management.
Beneficial predatory mites for whitefly control
Predatory mites (Amblyseius swirskii) are valuable biological control agents that feed on whitefly eggs and young nymphs (crawlers). Unlike specialized predators, A. swirskii can also survive on pollen and alternative food sources when target pests are scarce, making it particularly useful for preventive biological control. These mites actively search plant foliage, especially the undersides of leaves, for whitefly eggs and young nymphs, reducing the number of immature whiteflies that develop into reproductive adults.
Recommended release rates:
- Preventive control: Introduce 25 mites/m² early in the crop production cycle.
- Light infestation: Release 50 mites/m² when whiteflies are first detected.
- Heavy infestation: Apply 100–300 mites/m² in targeted areas.
Distribute mites as evenly as possible throughout the greenhouse canopy, paying particular attention to the undersides of leaves. Breeding sachets can be used to provide a continuous supply of predatory mites. Maintain suitable greenhouse temperatures and humidity to support mite establishment and activity. A. swirskii performs best under relatively warm conditions, generally between 20–32°C (68–86°F). Adequate humidity and alternative food availability further improve its establishment and effectiveness.
Parasitic wasps for greenhouse whitefly management
Parasitic wasps are among the most effective biological control agents for greenhouse whiteflies. Unlike predatory mites, which feed on whitefly eggs and young nymphs, parasitoid wasps lay their eggs inside or beneath immature whitefly hosts. The developing parasitoid larvae eventually kill the whiteflies. Two important commercially available species, Encarsia formosa and Eretmocerus eremicus, are commonly used in commercial greenhouse production.
A. Encarsia formosa – The greenhouse whitefly parasitoid
Encarsia formosa is particularly effective against greenhouse whitefly (Trialeurodes vaporariorum) and is widely used in greenhouse tomato, cucumber, pepper, and ornamental crops. Adult female wasps search the undersides of leaves for suitable whitefly nymphs and lay their eggs inside them. The parasitoid larvae develop within the whiteflies, eventually killing their hosts. Parasitized greenhouse whitefly pupae turn black, providing growers with a visible indicator of successful biological control. Adult female Encarsia can also feed directly on whitefly nymphs, further reducing pest populations.
Recommended release rates:
- Preventive control: Release 1–2 wasps/m² weekly early in the crop production cycle.
- Light infestation: Release 4–5 wasps/m² weekly when whiteflies are first detected.
- Heavy infestation: Release 10–30 wasps/m² in targeted areas.
Distribute parasitoid cards evenly throughout the greenhouse, placing them in shaded areas within the crop canopy and avoiding direct sunlight. Avoid removing leaves containing parasitized whitefly pupae before adult wasps emerge. Encarsia formosa generally performs well at temperatures of approximately 20–26°C (68–79°F).
B. Eretmocerus eremicus – A valuable whitefly parasitoid
Eretmocerus eremicus attacks both greenhouse whitefly and sweetpotato whitefly (Bemisia tabaci), making it a valuable biological control agent when both species are present. It performs particularly well in warm greenhouse environments, generally between 20–30°C (68–86°F), and is suitable for short-term ornamental crop production. Adult female wasps search for immature whiteflies and deposit their eggs beneath or near the host nymphs. After hatching, the parasitoid larvae enter the whiteflies and develop internally, eventually killing their hosts. Adult females also feed on whitefly nymphs, providing additional control through host feeding.
Recommended release rates:
- Preventive control: Release 2–3 wasps/m² weekly early in the crop production cycle.
- Light infestation: Release 4–5 wasps/m² weekly when whiteflies are first detected.
- Heavy infestation: Release 10–30 wasps/m² in targeted areas.
Application guidelines:
Introduce parasitoid s as early as possible. Hang release cards evenly throughout the greenhouse, preferably above the crop canopy. Avoid direct sunlight and excessive heat. Continue weekly releases while monitoring whitefly populations.
Combining predatory mites and parasitic wasps
One of the most effective strategies for managing greenhouse whiteflies is combining different beneficial organisms. This approach works because each natural enemy attacks different whitefly stages.
For example:
- Amblyseius swirskii feeds on whitefly eggs and young nymphs.
- Encarsia formosa parasitizes developing whitefly nymphs.
- Eretmocerus eremicus attacks immature whiteflies and also kills additional nymphs through host feeding.
Conclusion
Biological control offers greenhouse growers an effective and sustainable way to manage whitefly infestations while reducing dependence on conventional insecticides. The most useful beneficial organisms include:
- Amblyseius swirskii for preventive control of whitefly eggs and young nymphs.
- Encarsia formosa for controlling greenhouse whitefly, particularly on long-term crops.
- Eretmocerus eremicus for managing greenhouse and sweetpotato whiteflies, particularly under warmer conditions.
For best results, introduce beneficial organisms early, follow appropriate release rates, maintain good greenhouse sanitation, and monitor pest populations regularly.