Thrips (thysanoptera) are a common, widespread pest that affect a variety of host. They are small, winged insects that feed on host plant tissue by piercing the outer layer of the tissue and sucking out the contents of the cell. Feeding damage can appear as discoloration, stippling, or scarring on leaf tissue or fruits. They can also vector plant pathogens. Some thrips species may feed on fungal spores or pollen, and some species are beneficial insects that feed on mites, or other insects, but this guide will focus primarily on thrips as plant pests. 

Onion Thrips
Onion Thrips

Thrips are widespread, in part because they are so small and can be transported long distances through wind, or on plant material. In some cases thrips may be introduced from other areas, and become pests in the new area.

Thrips Identification

Adult thrips are slender, elongate and small (less than 1/20 inch.) They typically have fringes on the margins of both pairs of their wings, which are long and narrow. Immature thrips at the larvae or nymph stage do not have wings, but are still elongated. The color of thrips can range from translucent white to yellow, green, brown or black. Some thrips species are brightly colored, and some species may change colors as they mature from nymphs to adults.

Because of their size, thrips species identification can be difficult without a microscope or hand lens. Experts are usually needed for a positive identification to the species level. Feeding damage, insect behavior, and host plant can all provide clues to thrips identification, in addition to the body appearance. However, recommended chemical control of different thrips species is usually very similar, so a species level identification is not always needed.

Species identification can be more important for integrated pest management programs. Beneficial insects that feed on thrips usually have specific species preferences. Also some thrips may be harmful on some host plants and not harmful on others. For example, Citrus thrips are widespread on a variety of plants, but typically only damage citrus and blueberries. If these thrips are found on a different plant host, no action would be needed.

Thrips Life Cycle

The thrips life cycle begins in the egg stage, before the thrips hatch and begin development. Eggs are long and cylindrical, and are laid on leaves, buds, or other locations where emerging larvae may be able to feed.

There are two larval stages in which feeding occurs, and two non feeding stages: the prepupa and pupa stage. (These stages are not true pupal stages, but are called this because of the great change in appearance and behaviour.) The prepupae and pupae usually drop to the soil or lodge themselves into plant crevices or galls, before emerging as adults.

Thrips may have many life cycles in a year. During periods of warm weather, the entire lifecycle can be completed as quickly as 2 weeks.

The Pest Prophet app can be used to track and predict thrips’ life cycle changes using insect growing degree day models and can be used to help time scouting and management decisions.

Thrips Damage

Thrips feed through piercing and sucking. They can damage fruit leaves, and other plant tissues, which can affect the host plant’s appearance. Thrips rarely damage trees or shrubs enough to kill the plants, but ornamentals may be susceptible to cosmetic damage. Some vegetable crops may have economically significant damage to the plant tissue. Thrips can also vector viruses in some plants.

Tomato Spotted Wilt Virus

Feeding from thrips can stunt plant growth and cause stippling (spots) or distortion in the leaves. In some cases, heavily damaged leaves may drop from the plant. Flower petals can be discolored from thrips feeding on flower buds, even before they open. On some plants, terminal growth can be stunted as well. Cuban laurel thrips create galls on the leaves.

Western flower thrips  can damage flowers, such as roses, with petal discoloration as a result of thrips feeding. Western flower thrips also vector some potentially devastating diseases, such as Impatiens necrotic spot virus or Tomato spotted wilt virus .

Scarring on avocados.

On avocados, thrips can cause brown or silver scarring on the fruit. Citrus thrips can cause similar symptoms on citrus. In both cases, the internal fruit quality is unaffected. Thrips feeding on grapes, apples, nectarines, or raspberries can result in scarred or deformed fruit. Citrus thrips can also reduce blueberry yields by feed on shoot tips, causing loss of foliage.

Sometimes damage from thrips feeding may be observed well after the damage has occurred, for example after flower buds open. This may be too late for control options. Also, thrips damage can sometimes be challenging to identify because of how similar it appears to other abiotic disorders or pathogens. Thrips usually need to be present and identified for damage to be attributed to them. 

Thrips Management

Thrips can be very challenging to control. An integrated pest management program is recommended to provide sustainable long term control. This can be a combination of cultural practices, beneficial insects and natural enemies, and selective use of insecticides that are specifically targeted. 

Thrips Monitoring

If thrips are suspected, adults can me monitored by gently shaking foliage or branches onto a sheet of paper or cloth. Some thrips may feed in enclosed buds or shoot tips. These can be monitored by clipping these plant parts and placing them into a jar with 70% alcohol before shaking. This solution can be filtered through paper and thrips can be observed.

 Watch the online video demonstration of this technique:

Adult thrips can also be monitored with yellow sticky traps. The presence of thrips does not always indicate that action is needed though, specific species and host plants but be considered. Plants that appear to be infected with thrips-vectored viruses need to be sent to local plant pathology lab or extensionist for confirmation.

Biological Control Methods

There are predators of thrips such as: predatory thrips, green lacewings, minute pirate bugs, mites and parasitic wasps. These predators may be purchased and released, but naturally occurring populations can also be conserved and augmented through careful management. Avoiding dust, and broad use pesticides can help maintain natural predator populations. Diverse plant hosts near within or near the field can also help encourage growth of natural predators.

Aeolothrips, a predatory thrips species

Specific predators may have different levels of effectiveness for different thrips species. For example, Cuban Laurel thrips are best controlled by minute pirate bugs and green lacewing larvae. Citrus thrips are better control by Euseiues mites. Greenhouse thrips can be controlled effectively in some areas by the parasitic wasp, Megaphragma mymaripenne, which parasitized thrips eggs, or Thripobius semiluteus paratizes the larvae of greenhouse thrips.

Broadly releasing natural predators may have mixed results for thrips control, and may not be effective in every situation.

Cultural Control of Thrips

There are many cultural practices that can be used to improve the management of thrips. Different plants have different levels of susceptibility, so planting more resistant plants in higher risk areas can help prevent thrips infestation. Avoiding plant stress can also reduce the risk of thrips. Plants that are water stressed, or not receiving enough sunlight or nutrients, can be more susceptible to infestation from thrips. Keeping plants irrigated and fertilized (without excess fertilization), while removing old plant material can help reduce stress to plants. Specific cultivars can also react to thrips differently. For example, white and light colored roses are damaged more easily by Westen Flower Thrips than darker cultivars. The “Green Gem” cultivar of Indian laurel fig is mostly resistant to Cuban laurel thrips, which can be a huge problem on other cultivars.

Plant Pruning

Plant material that has been infested and damaged by thrips, should be pruned and removed from the garden or orchard. Pruning plants by cutting just above branch nodes instead of shearing new terminals can help to reduce growth of thrips-susceptible new growth.

Pruning during specific times of the year can also help control some species of thrips. Indian laurel figs that have been damaged by Cuban laurel thrips, should have the galled, and damaged terminals pruned in winter. This action will remove nearly all of the cuban laurel thrips which cannot survive during winter outside of the galls. This can greatly reduce damage by Cuban laurel thrips during the next season.

Early pruning of Avocado, for example in January, can help to reduce scarring on fruit due to thrips. This is because earlier pruning can stimulate the development of foliage earlier in spring. Thrips will prefer to feed on the succulent leaves, and less will move to the fruit.

Careful pruning of citrus trees in the interior of the trees can increase predaceous mite populations in the exterior canopy. This can help reduce the population of Citrus thrips, and reduce fruit scarring.

Row Covers and Mesh Cages

Using row covers, or other types of fine mesh cages on young herbaceous plants can be helpful to keep out thrips, as well as other insects, and keep them from feeding on the young plants. Row covers can be especially helpful before crops emerge or just after planting. Covers should be removed when the weather gets warmer and/or plants are larger and hardier. 

The specific type of row cover should prevent insects, but still allow light penetration and air movement. In some cases, “floating” row covers may be used where the plant lifts the cover as it grows. For plants with sensitive grow tips or that grow upright, some sort of frame should be used with wires strung between posts to hold the row covers above the plants. 

Reflective Mulch for Thrips Management

Reflective mulch can be a useful tool in controlling thrips. It can reflect light that interferes with thrips’s ability to fly and locate plants, which can reduce or delay infestation of young plants. It can be effective against winged aphids, leafhoppers and whiteflies, as well as thrips. For flowers and vegetables that are susceptible to thrips-vectored diseases, reflective mulches can be more cost efficient and effective that insecticides, in many cases. There are different types of reflective mulches, but silver or gray is usually the most effective. In home gardens, aluminum foil can achieve many of the same effects as larger, commercial mulches.

Silver reflective mulch on tomatoes

As plants grow and their canopy begins to cover the reflective mulch, it is less effective against flying insects. However, by this point in the plant’s development, it is usually hardier and less susceptible to thrips damage. Reflective mulches can also improve growth of some crops by increasing light and warming soil. There are also benefits for weed control and retaining soil moisture. However, some root diseases may be helped by reflective mulches.

Some other types of mulches such as straw or can also repel some pests, or encourage some predators, but this is not as well documented and results will depend heavily on specific situation.

Chemical Control of Thrips

In most home gardens and landscapes, thrips damage does not warrant chemical control. In many cases, by the time symptoms of feeding damage are observed, it is too late to provide adequate chemical control. Damaged plant tissue will not recover, even if the thrips population is treated.

In cases of where thrips-vectored plant viruses are a risk, insecticides likely will not be adequate to control thrips populations fast enough to prevent virus vectoring. Row covers, plastic mulch, or other preventative methods are typically more effective to prevent thrips infestation and virus vectoring.

Adult thrips, because of their mobility, can be difficult to control effectively with insecticides. Their eggs and pupal stages are also usually protected in plant tissue, and are also difficult to control through spraying. Inadequate spray coverage, and poor application timing can also result in poor results with chemical control. Some broad use pesticides can also hurt natural predator populations and result in more thrips later in the season.

If chemical control is considered as part of an integrated pest management program, special attention should be given to which product and active ingredients are used, and also to time the applications for best effectiveness. For more information about using weather based models to time pesticide applications use these guides:

Insecticide Types and Risks

Contact insecticides can be effective for greenhouse thrips and other thrips species that feed directly on plant tissue. Most of these products, if they do not leave residue, have very low toxicity to pollinators and other beneficial insects. Some of these products include: azadirachtin, insecticidal soaps, oil, neem oil, and some pyrethrins.

Because contact insecticides only affect what they can directly touch, adequate spray coverage is needed to reach all buds, shoot tips, and all other plant parts where thrips may be. Repeated sprays may also be needed to provide adequate control.

Spinosad based products can be very effective against thrips. Spinosad lasts on the plant a week or more, and can have some translaminar activity which can help be more effective against thrips. However, spinosad can pose some risk to bees and other natural enemies such as predatory mites, so spinosads should be avoided on flowering plants, and should be used carefully.

Systemic insecticides are types of insecticides that absorbed by the plants and can move to all plant parts, even the parts that were not directly sprayed. Systemic insecticide sprays can provide rapid and effective thrips control, depending on the active ingredient. For example neonicotinoids can vary in their effectiveness, and imidacloprid does not typically have very good results with thrips. These types of insecticides can have adverse effects on pollinators and natural enemies. Using systemic insecticides should be avoided during flowering, unless the product label states otherwise.

Organophosphates, pyrethroids and carbamates should be avoided for thrips control. These products usually have little effect on thrips, and can severely harm natural predators and pollinators. Spider mite outbreaks can often occur after using these products, because their predators will be eliminated.There is also risk of toxic effect to animals, or water runoff contamination.

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