Overview:
- What are thrips?
- What are the different types of thrips?
- What is the impact of thrips?
- How do I know if I have a thrips problem?
- How do I get rid of thrips?
- Summary
Thrips are tiny insects with fringed wings. There are over 6,000 documented species of thrips. Some are pests that cause significant damage to various crops, including onions, tomatoes, strawberries, and grapes, while others benefit agriculture because they feed on pests. In Canada, thrips are a significant pest in the agriculture and forestry industries. They can spread rapidly across long distances, are known to carry plant diseases, and can produce eight generations per year. This means their numbers can increase quickly and makes thrips difficult to control. Fortunately, many biological control methods exist for dealing with this common pest without harsh chemicals.
This article will provide an overview of thrips species, plant damage caused by thrips, and strategies for controlling them.
What are thrips?
Thrips measure between 0.5 and 13 mm in length. They have a wide global distribution, and many of the 6,300 thrips species are considered invasive. Thrips damage plants by breaking through the outer layer of plants and feeding on the contents. Thrips species can differ significantly in appearance, occurring in various colours depending on the species and life cycle stage. Larvae are generally transparent and smaller than adults. Many adult thrips have long, slender wings lined with small hairs on the edges. Thrip eggs are typically elongated and can appear kidney-shaped. Thrip species living in the tropics usually grow larger than those in temperate climates.
Thrips’ life cycle and mating strategies differ across species. Depending on the species and climate, thrips can have up to eight generations per year. Female thrips lay eggs on the leaves of host plants, and the larva begins feeding after hatching. The larvae progress through four stages (two feeding and two non-feeding) before developing into adults. In warmer climates, the progression to adulthood is faster. Thrips can survive the winter depending on the climate and species, but their numbers are typically reduced during this season.
What are the different types of thrips?
There are thousands of thrips species with different impacts on crops. Many are harmless, but some species have emerged as significant pests that damage crop yield, impacting several economically important industries. All thrips species belong to the taxonomic insect order Thysanoptera.
Greenhouse thrips (Heliothrips haemorrhoidalis)
These are a small, black-coloured species that are common pests in greenhouses. Host plants of greenhouse thrips include peppers and citrus plants. The species originated from tropical regions but now have a global distribution and are considered a significant pest for many plant types.
Western flower thrips (Frankliniella occidentalis)
Adults of this species are usually yellow or light brown and are 1-1.5 mm long. The species originated in North America but now has a global distribution. These thrips are significant pests because they feed on many different crop types and transfer damaging diseases to plants. Common crops damaged by western flower thrips include tomatoes, peppers, strawberries, and grapes.
Onion thrips (Thrips tabaci)
Onion thrips are also yellow or light-brown in colour but originate in Eurasia. As the name suggests, they affect onion crops, but they also cause damage to plants like garlic, carrots, and cabbage. They also transmit diseases and have a wide global distribution.
What is the impact of thrips?
Thrips species feed on plants by penetrating the harder outer layer to access the fluids inside. Depending on the species and host plant, thrips can feed on fruit, leaves, and shoots. Thrips can cause stunted growth and loss of yield, particularly with large infestations. They can also attack many large tree species, which are typically more resilient than fruits and vegetables.
Thrips also spread plant viruses. Common viruses include the impatiens necrotic spot virus and the tomato-spotted wilt virus. In Ontario, the tomato-spotted wilt virus significantly affects tomato and pepper crops. Managing this virus poses a particular challenge due to thrips’ ability to travel and cause infections across different fields.
How do I know if I have a thrips problem?
Thrips crop damage is easily noticeable, though the precise symptoms differ between thrips species and host plant types. Depending on the species, the damage leads to leaf wilting, brown and white spots, or a silvery or scaly appearance. Thrips also leave black droppings on the surface of leaves, which is sometimes referred to as frass. Thrips are too small to be easily noticeable to the naked eye. However, they can be easily seen using a magnifying glass.
Larger numbers of thrips will lead to a noticeable loss of yield and more extensive leaf damage. Thrips droppings will build up more quickly, and the thrips will be more evident to the naked eye. Symptoms of common thrips-associated viruses like brown rings on leaves (tomato-spotted wilt virus) may also be more visible. Some fungal infections are more likely when thrips cause significant damage.
How do I get rid of thrips?
Fortunately, there are many strategies for getting rid of thrips. Biological control mechanisms offer the best option for dealing with these pests without damaging the environment or depleting the number of beneficial organisms.
Monitoring for thrips
If thrips have been an issue in previous growing seasons or you suspect you have an emerging infestation, there are effective ways to monitor your crops.
- Gently shaking branches onto a white sheet of paper is a good way to identify the extent of the thrips problem
- Another option is to use brightly-coloured sticky traps near plants.
Cultural control options
In agriculture, cultural control refers to implementing practices that reduce or remove unwanted pests by making the crop environment less suitable for them. Some ideas include:
- Planting vulnerable crops, including seedlings, away from areas with many weeds can help prevent thrips from transferring between different host plants.
- If you notice an infested plant or plant part, you can cut it away and destroy it without bringing it into contact with other plants.
- Many thrips survive winter in fallen plant material, so removing plant debris and cutting away old plant parts, such as blossoms, which can harbour thrips, can help lower their numbers.
Biological control
Biological control methods use safer methodologies derived from nature. Many strategies for thrips biocontrol offer effective pest control without damaging the environment or ecosystem.
Macrobials
Macrobials are a type of biocontrol product commonly used against thrips. They are small animals that can be released in the crop field to reduce pest numbers. Lacewings are used to combat thrips and act by feeding on them directly. Predatory mites, such as Amblyseius swirskii, are a common and practical biological control product to combat thrips due to their ease of use. Additionally, nematodes are tiny worms that can be applied on crop leaves to feed on thrips pupae (an early thrip developmental stage).
Thrips also have many natural enemies that are already present in the environment. These predators include green lacewings and minute pirate bugs, and you can encourage them by providing a diverse ecosystem of plants and not using chemical pesticides.
Natural substances
Natural substances are biopesticides that offer a safe and natural solution to many pests. Neem oil, derived from the neem plant, is used as a repellent for thrips and a disruptor of larval growth and thrips reproduction cycles. It can also help get rid of scale insects. Mineral oil is also used for the suffocation and desiccation (drying out) of thrips.
Microbials
Microbials are another group of biopesticides but consist of microscopic organisms like bacteria, fungi, and viruses. Beauveria bassiana is a type of fungus that occurs naturally in many soils. It is pathogenic to thrips and kills them by producing toxins. Another fungus called Metarhizium anisopliae can control thrips numbers through a similar mechanism to Beauveria bassiana. Both of these options offer an environmentally friendly solution to thrips infestation.
Other methods
Reflective mulch can disrupt thrips’ ability to find new host plants. It can be used with other methods as part of integrative pest management strategies.
Chemical pesticides
As a world leader in nature-based pest management knowledge implementation, CABI encourages Integrated Pest Management (IPM) as the preferred, ecologically-based approach to producing healthy crops. This approach allows for chemical pesticide use only as needed, and when adhering to measures that limit the exposure of people and the environment to them (see FAO, International Code of Conduct on Pesticide Management).
Before considering the use of chemical pesticides, farmers should explore all available non-chemical control solutions. These include cultural practices as mentioned earlier and consulting the CABI BioProtection Portal for identifying and applying suitable biological control products.
In case chemical pesticides are considered for use, farmers should look to select lower-risk chemical pesticides which, when used as part of an IPM strategy, help manage pest problems while minimizing harmful effects on human health and the environment. Agricultural advisory service providers can provide information on lower-risk chemical pesticides that are locally available and are compatible within an IPM strategy. These experts can also advise on the required personal protective equipment.
Summary
Thrips present a significant challenge to agriculture, including in Canada. They damage a variety of crops and spread plant diseases. Effective management requires early detection, cultural practices to reduce infestations, and environmentally friendly biological controls. Releasing predators, beneficial nematodes and using biopesticides like neem oil and beneficial fungi can reduce thrip damage. While chemical pesticides can be used, they come with ecological and health risks. Farmers can apply appropriate treatments to maintain healthy and productive crops by understanding the specific thrip species and their impacts.
Visit the CABI BioProtection Portal for solutions to your pest problem, or take a look at some of our other guides, such as how to get rid of spider mites and how to use the predatory mite Amblyseius swirskii to deal with thrips.
