Western Flower Thrips: The Damage Caused and Control Tips

Known in scientific circles as Frankliniella occidentalis, this thrip species is native to the western United States and Canada but has since invaded Europe, Africa, and South America.

The females are 1/16” inches long and vary in color from dark brown to red or yellow. They sometimes change with the season. 

Males are uncommon and measure only 3/64” inches long, always a pale yellow color.

The female can produce males using unfertilized eggs but only produce females from fertilized eggs in a process known as arrhenotokous parthenogenesis.

As with all thrips, the western flower thrip is a piercing insect that feeds on plant sap.

Their active lifespan may last anywhere from about 3 weeks to more than 8 weeks, depending on environmental conditions. They love greenhouse conditions!

Females will lay anywhere from 40 to more than 100 eggs on a host plant, usually in the fruit or flower.

Once hatched, the nymphs spend their first two instars feeding off the plant. They then spend the last two instars in the soil.

Western flower thrips like bright colors and may even bite humans wearing bright blues, whites, or yellows. 

While the bites are harmless, they can cause some minor skin irritation.

What Damage do Western Flower Thrips Cause?

These little nasties attack more than 500 different plant species, including but not limited to:

  • African violets
  • Chrysanthemums
  • Geraniums
  • Gerberas
  • Gladiolus
  • Gloxinias
  • Impatiens
  • Pepper
  • Poinsettias
  • Pumpkin
  • Roses
  • Squash 
  • Tomato
  • Watermelon

The egg-laying process itself can cause scarring and open the door to infections.

Feeding will cause silvery flecks, distorted petals, streaking or discoloration, bud drop, and curled or otherwise deformed young leaves with whitish bumps on their upper surface.

Even worse, these thrips are vectors for several devastating diseases, such as impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV).

How To Control Western Flower Thrips?

Despite being prolific and capable of such damage, the western flower thrip is quite easy to eliminate. There are three tried-and-true natural methods.

NOTE: most insecticides marked for thrips will work on this species, although they may harm beneficial insects or even affect your plants; use sparingly and with caution.

Related: Controlling Thrips On Hibiscus

Natural Predators – Biological Controls

Chances are, you’ve got some staunch allies already living in your garden, especially if you have rosemary, marigolds, or other attractive plants growing.

Ladybugs, parasitic wasps, and lacewings will all hunt down and feed on thrips, requiring little in return for their services.

If you don’t have any hanging around, you can buy some online.

They will migrate if you don’t practice complementary planting with species they like.

Also, pesticides or insecticides of any sort can harm the good and bad bugs, so don’t invest in a batch of 500 ladybugs if you’re planning to do a chemical spray.

Neem Foliar Spray

One of the most popular natural remedies out there, neem foliar spray, kills on direct contact by suffocating the target.

The Advantages:

  • Dissipates without residue in 45 minutes to 1 hour, so it won’t harm beneficial insects if sprayed around dusk or dawn
  • Highly effective and won’t create superbugs
  • Useful indoors and outdoors, as well as on food crops 24 hours before harvesting
  • Non-toxic to humans, pets, or most wildlife 
  • Reapply every other day for 14 days or until the infestation is gone, then apply once every 14 days as a preventative
  • Won’t harm most plants

The Disadvantages:

  • Cannot be used near beehives or inhabited water features, as it can harm some aquatic life. Read Is Neem Oil Safe for Bees?
  • The plant must be thoroughly coated
  • Won’t harm bugs without direct contact

Neem Soil Soak

The plant absorbs the raw neem in a soil soak and serves as a systemic insecticide. It kills entire colonies by interrupting the signal to feed and by disrupting the growth and reproductive cycles. This will cause the whole colony to die out in just a few weeks.

The Advantages:

  • Food crops are ok to harvest 24 hours after treatment
  • Kills or combats many forms of fungal and microbial infection, including some forms of root rot in their early stages
  • May be applied once every 2 to 3 weeks as a preventative
  • Non-toxic to both humans and pets
  • Only affects bugs that bite or pierce the plant’s surface
  • Protects a plant for up to 22 days
  • Safe for use with most plants
  • Won’t harm earthworms or beneficial nematodes
  • Won’t produce superbugs

The Disadvantages:

  • Can’t be used close to inhabited water features
  • May cause minor chemical burns to plants if splashed
  • Takes longer to see results

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