How Some Thrips are Destructive While Others Help Control Insect Pests

One Thrips on a Stylidium leptocalyx flowerPhoto: Jean and Fred Hort

If you’re a keen gardener, you may have already had a few encounters with thrips, but if, like many, you aren’t quite so green-fingered, then prepare to be informed! Thrips belong to a large family of insects. While some species of thrips harm crops and gardens, other species benefit people by preying on other insect pests. Let’s find out more about these fascinating little creatures!

Background on Thrips

The word “thrips” is both singular and plural; the little creature in the picture above, sitting on a flower, is a thrips. Thrips belong to the insect order Thysanoptera, meaning “fringed wing”.

A typical adult thrips is a slim and tiny-winged insect less than one-twentieth of an inch in length. Nymphs or larvae are around the same size and shape, but lack wings.

As insect pests, thrips damage plants by leaving scars on leaves, flowers or fruit. This may be directly due to their feeding habits, but, even worse, thrips can also spread plant viruses.

On the other hand, there are species of thrips that feed upon mites or other insect pests, and even on other thrips!

Then there are some thrips that are neither harmful nor beneficial, because they eat pollen or spores without harming the plants. Finally, some thrips only harm certain plants. As an example, the avocado thrips scars avocados, while citrus thrips cause no damage to avocados at all.

Why are Thrips Named “Fringed Wing”?

One Highly Magnified ThripsPhoto: Smith609

This highly magnified image of an adult thrips shows its fringed wings. Another description for the wing could be “feathery”.

How Do Thrips Travel?

Few thrips are able to fly well, but they are light and can travel on strong breezes.

People might also accidentally transport them along with infested plants, fruits or flowers.

A Thrips Family Portrait

Many Adult and Nymph Thrips with EggsPhoto: Maximilian Paradiz

This image shows thrips adults, nymphs, and eggs. As you can see, they are dwarfed by human fingers; the fingerprint ridges are very evident in this picture.

Was This Leaf Damaged by the Thrips?

One Tiny Thrips on a LeafPhoto: Maja Dumat

This leaf shows clear damage along its edges, although the only visible thrips is much closer to the center vein. However the leaf has some minor damage throughout, so finding this one thrips might be enough evidence to result in a verdict of “guilty”.

Another View of a Small Thrips

One Adult Thrips Dwarfed by Syrphid Fly on a DaisyPhoto: Gilles Gonthier

Here, a thrips shares a daisy with a syrphid fly that is many times its size. The daisy shows no sign of damage in this image. Possibly this particular thrips only eats pollen.

Only thrips pictures can truly convey how small they are compared with most of the insects that people would notice.

How to Kill Thrips, the Insect Pest

Avocado Tree and FruitPhoto: Alpha

Really, the first question for a gardener or a farmer is whether there is an infestation of thrips, or of some other insect pest. Lace bugs and various mites can damage plants or leave fecal specks that are easily mistaken as clues leading to thrips. Also, it is possible that the thrips are feeding on the mites, and so actually helping the gardener!

Once assured by a professional that thrips are a problem, several types of insect control might be used. Some thrips can be controlled using specific oil-based insecticides. For this approach, it may be wisest to leave the choice of thrips control product to a pest control professional or insect exterminator.

However, biological control is another option. This consists of acquiring and releasing predatory insects, including other thrips, pirate bugs or specific types of mites. This approach requires expert knowledge. For example, any one species of parasitic wasp might be very selective in its choice of victim. Releasing an inappropriate control species will obviously not deal with the current infestation.

Covering low plants with a cloth mesh might help keep the thrips from the plants while still letting in air, light and rain.

Another method used to control thrips is to remove alternative host plants. The garden variety word for this kind of insect control is “weeding”. An additional trick used by avocado growers is to prune earlier than usual, as the thrips might keep feeding on new leaves rather than moving to the fruit.

The overall advice on thrips control is to seek a solution that is tailored specifically to the type of thrips and the local conditions.

Life Cycle of the Thrips

Many Thrips NymphsPhoto: Mick Talbot

A thrips hatches from an egg to its first larval stage. It feeds during both larval stages, but goes without food during pupation. However, the metamorphosis is not considered “complete”, so some authors do not like to use the term “pupal stage”.

Generally the “pupa” will drop from the plant onto the ground, to burrow into the soil or mulch. Some species of thrips will pupate on or inside leaves instead.

Thrips can produce eight generations in one year, with a full life cycle as short as two weeks in ideal weather. We’re certainly the wiser about thrips now than we were!

Disclaimer: The information contained in this article is for educational purposes only and should not be used for diagnosis or treatment without the opinion of a professional. Any reader who is concerned about his or her garden, orchard or farm should contact a professional for advice.

References:

Dreistadt, Phillips and O’Donnell, University of California at Davis, “Thrips“, referenced July 9, 2012.

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