Onion thrips (Thrips tabaci) cause damage by piercing plant surface cells and extracting their contents, leading to cell death and visible silver-grey scarring on leaves. This type of feeding reduces the plant’s chlorophyll levels, limiting photosynthesis and overall plant vigor. Small black specks of excreta often accompany these feeding scars, providing a clear sign of infestation.

Thrips tabaci typically concentrates along the main leaf veins, especially where the veins intersect, which is where the most noticeable damage occurs. As infestations increase, the damaged areas can expand, and in severe cases, leaves may curl, dry, or shrivel entirely. While minor infestations may not cause immediate economic loss, high populations can lead to fruit deformities, particularly in crops like cucumber. In some regions, onion thrips are also recognized as vectors of Tomato Spotted Wilt Virus (TSWV), adding a serious disease risk to their direct feeding damage.

Onion thrips (Thrips tabaci) develop through six distinct stages: egg, two larval instars, prepupa, pupa, and adult. Eggs are laid within plant tissue—such as leaves, flower petals, or the soft parts of stems—using a saw-like ovipositor.

The larvae are light to yellowish-green in colour, with prominent red eyes and a relatively large head. As they mature, the colour of the adult thrips can vary depending on their diet and host plant.

Pupation typically occurs in the soil, but pupae can also be found in protected locations such as within flowers or on the undersides of leaves. The prepupal and pupal stages are non-feeding and mainly sedentary, only moving when disturbed. These stages are recognized by developing wing buds, with the pupa displaying longer, more developed wing structures and backward-curved antennae compared to the prepupa.

Preventing onion thrips begins with excluding them from the growing environment and reducing conditions that support their development. For greenhouse or indoor crops, install insect-proof screens on vents and doors to physically block their entry. Make sure all entry points are sealed, and avoid leaving doors open unnecessarily during warm weather when thrips activity is high.

Maintain strict sanitation in and around the growing area. Remove weeds and plant debris, both inside the facility and in surrounding areas, as these can serve as hosts or breeding grounds for thrips. Regularly inspect new plant material for signs of thrips before bringing it into your growing space. Quarantine incoming plants when possible to avoid introducing hidden populations.

Thrips are highly mobile and can spread quickly, so consistent monitoring is critical. Use blue or yellow sticky cards placed just above the crop canopy to detect their presence early. Check these traps frequently and rotate their placement to stay ahead of population hotspots. For crops particularly susceptible to thrips, such as cannabis, onions, cucumbers, or ornamentals, increase trap density during the spring and summer months when thrips pressure is highest.

Environmental management also plays a role in prevention. Thrips tend to thrive in hot, dry conditions, so maintaining adequate humidity and avoiding temperature spikes can help deter their population growth. Implement crop rotation when feasible, particularly for outdoor growers, to disrupt the thrips’ life cycle and reduce overwintering populations in soil or crop residue.

Managing onion thrips biologically is most effective when integrated early and maintained throughout the growing season. The first step is ongoing monitoring/mass trapping using blue or yellow sticky cards. Blue sticky cards are particularly attractive to thrips and should be placed just above the crop canopy. Yellow cards may also catch thrips but are less specific, attracting a broader range of insects.

For active control, predatory mites are a cornerstone of thrips biocontrol.

• Swirski (Amblyseius swirskii) is a top-choice for preventative and early curative control. It performs well in warm conditions and not only targets thrips larvae but can also feed on whiteflies and pollen, supporting its population.
• Thripex (Neoseiulus cucumeris) is another reliable predatory mite, particularly suited for cooler environments and effective against the first larval stages of onion thrips.
• Limonica (Amblydromalus limonicus) is excellent for high-pressure situations, especially in humid environments like cucumber crops. It feeds aggressively on thrips larvae and adapts well to both greenhouses and indoor grow rooms.
• Anso-Mite (Amblyseius andersoni) is a versatile predatory mite that functions in a broad temperature range, making it a good addition for fluctuating climates or as part of an early-season rotation.

To tackle the soil-dwelling pupal stages, which are often overlooked, introduce:

• Entomite-M (Stratiolaelaps scimitus), a predatory mite that lives in the growing medium and preys on thrips pupae, fungus gnat larvae, and other soil-dwelling pests.
• Entonem (Steinernema feltiae), a beneficial entomopathogenic nematode that parasitizes thrips pupae in the substrate. Once applied via drench or irrigation, it actively seeks out and infects the pupae, helping break the pest's life cycle from below.

In hotspots or severe infestations, Thripor (Orius insidiosus)—a generalist predatory bug—can provide fast knockdown. Orius adults and nymphs actively seek out and consume both larvae and adult thrips. While slower to establish, they are highly effective once established, particularly in flowering crops.

For additional support, Chrysopa (Chrysoperla carnea), the green lacewing, can be introduced as eggs or larvae. These voracious generalist predators feed on thrips larvae, aphids, and other soft-bodied pests. Chrysopa is especially useful for early intervention in mixed pest scenarios or outdoor crops where environmental conditions fluctuate.

When integrated properly, these biological control agents work synergistically to keep onion thrips populations below damaging thresholds—without the need for harsh chemical inputs