Thrips are tiny insects that can cause major damage to plants. But their small size makes them hard to spot. So how do you know if thrips are present? This article will cover how to identify thrips, where to look for them, and what their damage looks like.
What are thrips?
Thrips are tiny winged insects only 1-2 millimeters long. There are thousands of species of thrips. Some feed on plants by puncturing cells and sucking out the contents. Other species are predatory and feed on mites, eggs, or other small insects.
Thrips go through multiple life stages during their development. They begin as eggs, then hatch into nymphs that look like smaller wingless versions of the adults. Nymphs molt through 2 stages before reaching the winged adult form.
Adult thrips can vary in color from yellowish to dark brown or black. Their bodies are slender with long antennae and legs. When at rest, their wings are folded along the length of their backs.
Why are thrips problematic?
Thrips cause two major types of damage: direct feeding damage and viral transmission.
Feeding damage – Thrips use their piercing mouthparts to feed on plant cells. This causes white or silvery speckled patches on leaves, buds, flowers, and fruits. The patches eventually turn brown, and affected leaves may curl or distort. Heavy thrips damage can stunt plant growth.
Viral transmission – Some species of thrips spread damaging plant viruses as they feed. Viruses transmitted by thrips include tomato spotted wilt virus and impatiens necrotic spot virus.
Signs of thrips
Thrips can be challenging to detect because of their very small size. But there are some telltale signs that thrips may be present:
- Speckled or streaked leaves
- Silvery patches that turn brown
- Distorted growth and curled leaves
- Black dots of excrement on leaves and flowers
- Slowed or stunted growth
If you see these types of damage on your plants, thrips may be the culprit. The bugs themselves are difficult to spot without close inspection.
Where to look for thrips
Thrips mainly inhabit the protected parts of plants:
- Under leaves – Especially favored by thrips larvae.
- In leaf axils – The joint between the leaf stem and main stem.
- Along stems
- Inside flowers
- Under bracts and sepals
To inspect for thrips, take a damaged leaf, flower, or other plant part and do the following:
- Hold it close to a white sheet of paper.
- Gently brush the leaf surface to knock thrips onto the paper.
- Look for tiny yellow, brown, or black insects crawling on the paper.
- Use a hand lens to see them more clearly.
Leaf undersides and flowers are especially important places to check. The tiny larvae often congregate in these protected areas.
Thrips life cycle
Understanding the thrips life cycle helps explain when and where to look for them.
Eggs – Female thrips insert eggs into plant tissue using their saw-like ovipositor. The eggs are barely visible and hidden within the plant.
Larvae – Tiny first stage larvae hatch and feed on the plant. They progress through 2 larval stages that look like wingless versions of the adults.
Prepupae and pupae – In the final larval stage, prepupae form and drop to the soil. Pupation occurs in the soil or leaf litter.
Adults – Winged adults emerge from the soil to mate and lay more eggs on plants, renewing the cycle.
This life cycle means thrips spend part of their time in the soil or leaf litter. Sanitation by removing plant debris can help disrupt their development.
Thrips identification
If you find small insects on your inspection, how can you identify if they are thrips?
Here are some key thrips identification features:
- Adults 1-2 mm long
- Slender, straw-like bodies
- Long fringed wings folded over body
- Red, yellow, brown, or black in color
- Move rapidly when disturbed
- Mouthparts beak-like for piercing cells
Thrips can be confused with other small insects like fungus gnats or shore flies. But thrips have a very distinct slender body and long narrow wings.
Thrips management
If thrips are detected, taking action right away helps limit their damage. Effective thrips control involves:
- Removing infested plant parts – Prune off damaged leaves and flowers.
- Using insecticidal soap or neem oil – These organic options kill thrips on contact.
- Applying thrips-specific insecticides – Products with spinosad, spinetoram, or abamectin.
- Releasing predator insects – Minute pirate bugs and predatory mites eat thrips.
- Using reflective mulch – The silvery surface deters thrips from landing on plants.
Insecticides work best against the young larvae before they are tucked away inside flowers and leaves. Repeat applications are needed to control new generations.
Preventing thrips
Prevention is key to avoiding thrips damage:
- Check new plants for signs of thrips before bringing home.
- Quarantine plants away from existing collection.
- Remove weeds that can harbor thrips.
- Use pest exclusion row covers.
- Apply beneficial nematodes to soil to kill larvae.
- Use yellow or blue sticky traps to catch adults.
- Clean up and dispose of plant debris.
Common thrips species
There are many species of thrips that feed on plants. Some of the most common include:
| Species | Host Plants | Notes |
|---|---|---|
| Onion thrips | Onions, garlic, cabbage | Major onion pest |
| Western flower thrips | Flowers, fruits, vegetables | Transmits plant viruses |
| Chilli thrips | Peppers, tomatoes, citrus | Recent invasive pest |
| Plague thrips | Grapes, stone fruits, nuts | Common in California |
Knowing which thrips species infests your plants can help guide control strategies. Some pesticides are more effective on certain types of thrips.
Conclusion
Thrips are tiny pests capable of causing significant economic damage. Their small size makes them easy to miss at first. But telltale signs like leaf speckling, stunted plants, and dark excrement reveal their presence. Inspecting undersides of leaves and flowers is key to detection. Quick action to control thrips can help prevent lasting impacts. With vigilance and integrated pest management, thrips can be managed for healthy plants.