Thrips in Crops: Identification, Damage and Control Guide

September 3, 2026

Thrips: Identification, Crop Damage, Life Cycle and Integrated Control Guide

Introduction

Thrips are tiny insects belonging to the order Thysanoptera. Although they are difficult to see without magnification, some thrips species are economically important pests of vegetables, fruits, field crops and ornamental plants worldwide.

Two of the best-known agricultural pest species are the Western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci). Western flower thrips is particularly important because it has a very broad host range and can cause both direct feeding damage and indirect losses through transmission of plant viruses.

According to the European and Mediterranean Plant Protection Organization (EPPO), Frankliniella occidentalis has been recorded from 244 plant species in 62 plant families, demonstrating why this insect can move easily between different crops and production systems.

For growers, identifying thrips early is important because populations can develop inside flowers, buds and young leaves where conventional visual inspection may miss them.

What Do Thrips Look Like?

Thrips are extremely small, narrow-bodied insects.

Depending on the species and life stage, adults are generally around 0.5–1.5 mm long. Their most characteristic feature is the presence of narrow wings fringed with long hairs. Adults may range from pale yellow to brown or almost black, while immature stages are generally lighter colored and wingless.

Because of their small size, growers often notice crop symptoms before seeing the insects themselves.

A hand lens can make identification easier. For uncertain infestations, professional identification may be necessary because many thrips species look very similar but differ considerably in economic importance.

Thrips Life Cycle

Thrips have a distinctive developmental cycle consisting of:

Egg → First larval stage → Second larval stage → Prepupa → Pupa → Adult

Only the adults and first two immature stages normally feed on plants. The prepupal and pupal stages do not feed.

Female Western flower thrips can insert their eggs directly into plant tissue. After hatching, larvae begin feeding on tender plant tissues before eventually passing through non-feeding stages and becoming adults. Multiple generations may develop during a growing season when temperature and host availability are favorable.

This biology helps explain why control can be difficult. Eggs are protected inside plant tissues, larvae often hide in flowers or growing points, and some developmental stages may occur away from exposed leaf surfaces.

How Do Thrips Damage Plants?

Thrips possess rasping and sucking mouthparts.

Instead of simply piercing a single vascular tissue like many aphids, thrips damage surface cells and feed on released plant contents.

Typical feeding symptoms include:

Silvering or bronzing of leaves, distorted young growth, curling leaves, scarred fruit surfaces, discolored flowers and small dark fecal spots.

UC IPM notes that thrips feeding can cause silvery to dark brown discoloration, scarring, leaf deformation and damage to flowers and developing fruits.

Damage may become much more obvious as affected tissue expands. A tiny feeding injury on very young fruit, for example, can develop into a much larger scar as the fruit grows.

Why Are Flowers Especially Important?

Many important thrips species prefer flowers, buds and tender growing points.

Western flower thrips frequently feed inside flowers where pollen and young tissues provide attractive food sources. This protected feeding location also makes the insects difficult to reach.

Flower feeding may cause discoloration, streaking, reduced ornamental quality or damage to developing fruit.

In fruit crops such as nectarines and plums, feeding on very young fruit can produce scars that become larger as the fruit develops, potentially reducing market quality.

Which Crops Are Commonly Affected?

Thrips can occur on many economically important crops. Depending on the species, important hosts include:

Onion and garlic
Pepper and tomato
Cucumber and other cucurbits
Strawberry
Citrus and other fruits
Grapes
Mango
Cotton
Beans
Sunflower
Ornamental flowers and greenhouse crops

EPPO records Western flower thrips on numerous fruit, vegetable, field and ornamental hosts, including tomato, pepper, cucumber, strawberry, grape, mango, cotton and sunflower.

However, finding thrips on a crop does not automatically mean that economically important damage will occur. Correct species identification, population density and crop stage all matter.

Thrips Can Also Transmit Plant Viruses

Direct feeding is only part of the problem.

Certain thrips species are important vectors of plant viruses.

Western flower thrips can transmit tospoviruses such as Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INSV). In susceptible crops, these viruses may cause necrotic lesions, ringspots, distorted growth, reduced plant development and potentially severe production losses.

Tomato, pepper and several other vegetable and ornamental crops can therefore suffer damage even when direct thrips feeding appears relatively limited.

This is one reason virus-vector situations require a different management strategy from situations where cosmetic feeding injury is the only concern.

How Can Growers Detect Thrips Early?

Because thrips are small and often hidden, monitoring should begin before severe symptoms develop.

One simple method is to gently shake flowers or foliage over a piece of white paper. Thrips that fall onto the surface can then be inspected with a hand lens.

Blue or bright yellow sticky traps can also be used to monitor flying adults. UC IPM recommends sticky traps as a monitoring tool but emphasizes that the presence of adults on traps does not automatically prove that damaging populations are present on the crop.

Crop scouting should therefore combine trap information with direct inspection of flowers, growing points, young leaves and developing fruit.

Why Are Thrips Difficult to Control?

Several biological characteristics make thrips challenging pests.

They are extremely small, frequently hide inside flowers and buds, have multiple developmental stages and can move between different host plants. Eggs inserted into plant tissues are also protected from many external treatments.

In addition, insecticide resistance is a major concern, especially in Western flower thrips.

IRAC documents extensive resistance research for Frankliniella occidentalis, including field-evolved resistance to several insecticide classes in different parts of the world. Resistance has also been documented historically in populations from southeastern Spain and other intensive production areas.

This means repeatedly applying one insecticide—or several products that actually have the same mode of action—can quickly reduce the sustainability of a control program.

Integrated Thrips Management

Effective thrips management should rely on IPM — Integrated Pest Management, rather than insecticides alone.

Sanitation and exclusion are especially important in greenhouse production. Removing heavily infested plant material, managing alternative host vegetation carefully and preventing movement of infested seedlings can reduce pest pressure.

Natural enemies can also contribute to control. Predatory mites, predatory bugs and other beneficial organisms are used in some commercial greenhouse systems.

UC IPM specifically recommends combining cultural management, exclusion, natural enemies and selective insecticides when treatment is justified.

Management should begin early because heavy populations hidden within flowers are generally much more difficult to suppress than small, newly developing infestations.

Insecticide Resistance Management

When insecticides are required, growers should first confirm which products are registered for the crop and thrips species in their country.

Rotation should be based on IRAC Mode of Action groups, not simply different commercial brand names.

For example, repeatedly changing between different products that belong to the same IRAC group may provide little resistance-management benefit.

IRAC resources on Western flower thrips emphasize resistance management and integration of chemical treatments with IPM practices.

The exact active ingredients available differ greatly between countries, crops and resistance situations, so there is no single insecticide program that is appropriate everywhere.

Common Reasons Thrips Control Fails

Poor results do not necessarily mean that an insecticide itself is ineffective.

A control program may fail because insects are hidden deep inside flowers, populations were already too high when treatment began, the wrong thrips species was identified, spray coverage was inadequate, environmental conditions reduced performance or the population has developed resistance.

Another common problem is focusing only on adults.

A crop may contain eggs, larvae, pupae and adults at the same time. Suppressing only one life stage can allow the population to recover.

For this reason, monitoring after treatment remains important.

Thrips and Climate

Thrips populations often develop rapidly during warm conditions when suitable host plants are abundant.

Their light bodies and fringed wings also allow adults to move with air currents and migrate from surrounding vegetation into crops. UC IPM notes that disturbance or drying of flowering vegetation near fields or orchards can sometimes drive thrips into crops.

Crop surroundings should therefore be managed carefully rather than assuming that removing all nearby vegetation immediately will always reduce thrips pressure.

Frequently Asked Questions

How can I tell whether crop damage is caused by thrips?

Look for silvering, bronzing, surface scarring, distorted young leaves, flower damage and small dark fecal spots. Shake flowers or leaves onto white paper and inspect the insects with a hand lens.

How small are thrips?

Most economically important species are only around 0.5–1.5 mm long, making them difficult to detect without close inspection.

How do thrips spread plant diseases?

Certain species, particularly Western flower thrips, can acquire and transmit important tospoviruses while feeding on susceptible plants.

How should growers manage insecticide resistance?

Avoid relying repeatedly on one mode of action. Rotate effective registered products according to their IRAC groups and combine chemical treatment with monitoring, sanitation, biological control and other IPM measures.

How can thrips be monitored?

Inspect flowers and growing points, shake plant material over white paper and use blue or yellow sticky traps to monitor flying adults.

Conclusion

Thrips may be tiny, but their agricultural importance can be substantial.

Species such as Western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci) can damage leaves, flowers and fruit while some species also transmit economically important plant viruses.

Their broad host range, concealed feeding behavior, rapid population development and ability to develop insecticide resistance make them difficult pests to manage with insecticides alone.

The most effective long-term strategy is therefore:

Correct Identification + Early Monitoring + Crop Sanitation + Biological Control + Selective Treatment + IRAC Mode-of-Action Rotation

For farmers and agricultural distributors, understanding the pest's biology is the first step toward choosing an appropriate management strategy rather than reacting only after serious crop damage appears.