Thrips Virus Transmission
Overview
Some thrips species transmit economically important plant viruses.
Western flower thrips (Frankliniella occidentalis) is particularly important in protected horticulture because it can transmit tospoviruses between susceptible plants.
Virus management depends on:
- preventing infected plant material entering the crop
- detecting thrips early
- suppressing larval and adult populations
- removing infected plants
- managing weed and crop reservoirs
Controlling visible feeding damage alone may not be enough to prevent virus spread.
Important viruses
Two important thrips-transmitted viruses are:
- Tomato spotted wilt virus (TSWV)
- Impatiens necrotic spot virus (INSV)
These viruses can affect:
- vegetables
- ornamentals
- propagation crops
- protected fruiting crops
- weed hosts
Symptoms vary by plant species and growing conditions.
How thrips acquire virus
Thrips generally acquire tospoviruses while feeding as young larvae on infected plant tissue.
The basic pathway is:
- A young larva feeds on an infected plant.
- Virus is acquired during feeding.
- The virus develops within the insect.
- The thrips completes development.
- The infected adult moves to healthy plants.
- Virus is transmitted during feeding.
Adults that did not acquire the virus during the susceptible larval stage do not normally become effective vectors simply by feeding on an infected plant later.
Why adults matter
Although virus acquisition occurs mainly during larval development, adults are important because they:
- fly between plants
- move between crop areas
- enter through vents and doors
- remain infective after acquisition
- may transmit virus before crop symptoms become obvious
This makes early larval suppression and adult monitoring equally important.
Virus transmission versus feeding damage
| Issue | Feeding damage | Virus transmission |
|---|---|---|
| Cause | Rasping and feeding on plant cells | Feeding by an infective thrips |
| Visibility | Silvering, scarring and black specks | Symptoms may appear later |
| Threshold | Depends on crop quality tolerance | Very low tolerance in vulnerable crops |
| Main response | Pest suppression | Pest suppression plus infected-plant removal |
| Monitoring | Flowers, leaves and traps | Thrips monitoring plus crop symptom checks |
A crop may suffer virus spread before major thrips feeding damage becomes visible.
Typical virus symptoms
Depending on the crop, symptoms may include:
- ringspots
- necrotic patches
- distorted growth
- stunting
- chlorotic markings
- leaf bronzing
- flower distortion
- uneven fruit colouring
- plant collapse
Symptoms should be confirmed using appropriate diagnostic testing because nutritional disorders, herbicide injury and other viruses may appear similar.
Main vector species
Western flower thrips
Western flower thrips is a major vector because it:
- reproduces rapidly
- feeds in flowers and young tissue
- develops well in protected crops
- moves readily between plants
- has a broad host range
Learn about Western Flower Thrips
Onion thrips
Onion thrips may also transmit important viruses in susceptible crops and production systems.
Species identification matters because vector competence and crop relevance differ between thrips species.
Virus reservoirs
Potential reservoirs include:
- infected crop plants
- symptomless plant material
- weeds
- volunteer plants
- old crop residues
- propagation stock
- neighbouring crops
Weed management should extend beyond the immediate production area where practical.
Propagation risk
Propagation crops are particularly vulnerable because:
- plants are young
- material moves between sites
- crops are densely spaced
- low thrips populations can spread quickly
- infected plants may enter before symptoms develop
Incoming plant material should be inspected and isolated where risk is significant.
Practical IPM strategy
A strong virus-risk programme combines:
- clean plant material
- early thrips detection
- preventative predatory mites
- Orius establishment where suitable
- weed and reservoir management
- rapid removal of suspect infected plants
- movement controls between crop areas
- compatible pesticide use where necessary
- diagnostic confirmation of suspicious symptoms
Biological control
Biological control can reduce vector pressure but cannot cure infected plants.
Important beneficials include:
Predatory mites mainly suppress young larval stages, while Orius may attack larger larvae and adults.
Key message
Virus-risk crops require a lower tolerance for thrips than crops where only cosmetic feeding damage matters.
Early detection, clean plant material and preventative biological control are essential because virus transmission may occur before visible thrips damage becomes widespread.