Thrips can cause a variety of plant damage and are easiest to get rid of using a combination of integrated pest management (IPM) techniques. There are more than 5000 known thrips species in the insect order Thysanoptera. Some species only feed on a few plants while others will feed on a wide variety.
Adult thrips have elongated bodies and fringed wings. They are 1/20th of an inch long and can be various colors. Understanding their life cycle is important when it comes to getting rid of thrips. The easiest life stages to get rid of are larvae and adults.
Thrips Life Cycle
The thrips’ life cycle has six distinct stages; egg, first instar larva, second instar larva, prepupa, pupa, and adult. Females lay their eggs in or on leaves and buds. This allows emerging larvae to start feeding immediately after hatching.
Larvae resemble the shape of adults but are wingless. They feed on plant tissue until they become large enough to pupate.
Thrips don’t have a true pupal stage, but they stop feeding and develop wings during their ‘pupal’ stages. Most species drop to the soil to pupate. This is the only stage of thrips you will find living in the soil. Some species pupate on the underside of leaves or in galls they create.
Under ideal conditions, thrips can complete their life cycle in two weeks. Adult females can reproduce sexually and asexually. Thrips can have up to 8 generations per year.
Types Of Damage Thrips Cause
Stippling of Plant Tissue
Thrips feed by puncturing plant tissue and sucking out juices from individual cells. This kills individual plant cells and causes a stippling effect of tiny yellow-to-white spots on leaves. Plant tissue with stippling won’t recover. Prune damaged areas to remove unsightly discoloration.
Plant Tissue Distortion
Some thrips species prefer to feed on new growth, shoots, and buds of plants. This feeding results in the distortion of plant tissue as it grows. Prune distorted plant tissue to improve the plant’s appearance.
Plant galls are caused by certain insect species feeding on them. Galls can occur on leaves, stems, buds, or flowers. They can appear as bumps, leaf curling, growths on stems, discoloration, or other deformities. Prune off plant tissue with galls as they often harbor thrips.
Thrips are vectors for many plant pathogens which cause disease. This is the most destructive and deadly damage thrips cause. Once thrips insert their mouthparts to feed, the disease has been transmitted. Many diseases vectored by thrips cannot be cured.
The most susceptible plants to diseases vectored by thrips are vegetables and herbaceous ornamentals. The best way to prevent disease transmission by thrips is to use row covers or fine mesh to keep them off plants.
Use Integrated Pest Management To Eliminate Thrips
The best way to eliminate thrips is with a combination of techniques known as integrated pest management (IPM). IPM for thrips includes monitoring, biological control, cultural control, and chemical control.
Monitoring for thrips is the first step since catching outbreaks early makes management easier. Use sticky cards placed in or around the plant and check them weekly. Blue and yellow sticky cards will attract the most thrips. Thrips populations are largest and most active during spring and early summer.
There are many natural enemies which get rid of thrips naturally through predation. Thrips predators include green lacewings, predatory thrips, minute pirate bugs, predatory mites, and parasitic wasps. Releasing these insects in gardens isn’t effective since they can fly away. To increase thrips predator populations naturally, you should limit the use of residual insecticides and increase plant diversity.
Prune damaged leaf tissue to reduce thrips populations. It is best to prune branches back to a node or crotch.
Thrips prefer to feed on new plant growth and terminals. Young, small plants tend to be most impacted by thrips which can significantly alter the overall growth form of the plant long term. Protect young plants with netting or row covers to prevent thrips damage.
The most effective chemical thrips treatment is spinosad. It is made from byproducts of soil bacterium. Spinosad has translaminar properties meaning it can move short distances within plant tissue making it effective against thrips hiding in galls or buds.
This thrips treatment lasts for about a week and may require more than one treatment for full control of thrips. Spinosad is harmful to some predators of thrips for about one day after spraying. Don’t treat plants for longer than necessary to limit damage to predator populations.
Plants That Repel Thrips
Rosemary is the only plant that has been proven to repel certain thrips. However, studies have shown that some plant essential oils can act as repellents of thrips. These include rosemary, onion, sweet marjoram, Acorus calamus, Melissa officinalis, and Juniperus virginiana.
Management Considerations For Thrips Indoors
Some IPM techniques can be used to get rid of thrips indoors. You can monitor for them with sticky cards. If plants become infested, prune off affected tissue to reduce populations.
The best insecticides to use indoors are pyrethrins, insecticidal soap, and neem oil. Make sure the chemical you purchase is labeled for indoor use.
Frequently Asked Questions
Thrips are often gone before you notice the damage they cause and early detection makes management easier. The quickest detection method is to gently shake flowers and leaves over a styrofoam cup. Thrips are easier to see against a white background and static makes them stick to the cup. Yellow or blue sticky cards also work great for detecting thrips.
A multipronged Integrated Pest Management (IPM) strategy is best for killing thrips. First, remove any heavily damaged or infested plant material by pruning. Second, increase predators of thrips in the area by providing a variety of plants and avoid using broad spectrum, residual pesticides. Only use contact insecticides that are non-residual such as neem oil or insecticidal soap.
The time it takes to get rid of thrips depends on the species and the control method used. Generally, it takes a minimum of 2 weeks. For example, if you use an insecticide such as neem oil, you’ll likely have to treat the plant at least twice and wait several days between treatments.
Thrips are not easy to get rid of due to their feeding methods and life cycle. Catching infestations early can make them easier to get rid of. You should regularly monitor for thrips on susceptible plants and act immediately if they are detected.
Thrips lay their eggs in a variety of places depending on the species. Some simply lay their eggs on the surface of vegetation while others will insert them into the leaf tissue. Other species will utilize the bud scales, which surround many flower and leaf buds, and lay their eggs within them for added protection.
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