Thrips, tiny and slender insects belonging to the order Thysanoptera, known for their fringed wings. With around 5,000 known species, they cause significant damage to crops either through direct feeding or by vectoring plant diseases. Interestingly, some species of thrips are predatory. This article aims to address the most common questions farmers have about thrips, offering insights into their behavior, damage, and effective control strategies
Characteristics of Thrips:
- Size and Appearance: Thrips are small, typically just 1-2 mm in length, and have slender bodies. They can be various colors, ranging from yellow and brown to black, and are often found on leaves, flowers, and fruits. To confirm their presence, farmers can shake affected plants onto a white background, where the thrips will be more visible.
- Mouthparts: Thrips have specialized feeding mouthparts that distinguish them from other insects like the Hemiptera (true bugs). Their mouthparts are asymmetrical, primarily characterized by a developed left mandible, while the right one is reduced or even absent in some species. Thrips use their left mandible in a scraping motion on the leaf surface, damaging the plant cells and causing them to ooze out sap, which the thrips then feed on. This process is often described as 'punching and sucking.' Some thrips species also introduce digestive enzymes into the plant tissue during feeding
- Fringed wings: Thrips possess distinctive fringed wings, which are not suited for conventional flight. Instead, they use a "clap and fling" mechanism for lift, this technique enables them to fly weakly but effectively. They can also disperse by wind or transported plant material.
Thrips undergo a complete metamorphosis, including egg, larva, pupa, and adult stages. The location of pupation varies depending on the species.
- Egg Stage: Female thrips lay their eggs in plant tissue, which can’t be seen without a microscope. The number of eggs laid by a single female thrip can vary but typically ranges from 50 to 100 eggs during her lifetime.
- Larval Stages: After hatching, thrips enter the larval stage. This stage has two instars. In the first instar, the larvae are tiny and translucent, feeding on plant sap. They grow rapidly and molt into the second instar, continuing to feed and grow.
- Pupal Stages: Following the larval stages, thrips enter the pupal stage, which also typically consists of two instars: the pre-pupa and the pupa. During these stages, thrips do not feed and often drop to the soil or hide in plant debris. The pupal stage is a time of transformation where they develop wings and other adult characteristics.
- Adult Stage: Emerging as adults, thrips are capable of flying and immediately begin feeding and reproducing. Adult thrips can live for about 1 month under optimal conditions.
Thrips have the ability to reproduce both sexually and asexually, with parthenogenesis enabling them to thrive independently. In greenhouses, where we often find warm temperatures, high humidity, and an abundance of nutritious plants, thrips experience a shortened life cycle and increased reproductive rates. This combination of asexual reproduction and ideal conditions leads to rapid population increases, resulting in serious infestations within a very short span of time.
Impact on Greenhouse Crops:
- Feeding Damage: Thrips feeding results in distinctive silvery or bronze scarring on the surface with dark spots which is its fecal matter. Excessive feeding can lead to stunted growth, deformed fruits and flowers, and sometimes even plant death.
- Virus Transmission: One of the most significant impacts of thrips is their role as vectors for plant viruses, especially the Tomato Spotted Wilt Virus and Impatiens Necrotic Spot Virus.
Management in Greenhouses:
In greenhouse environments, effective management of thrips involves a proactive approach, with regular monitoring being a key component.
Sticky Traps: Yellow, blue or green sticky traps can be placed throughout the greenhouse to capture thrips, providing a visual indication of their presence and population levels. The color of the trap used can vary depending on the thrip species, but generally, yellow works well for most species.
- Scouting: Regular, thorough inspections of plants are crucial. Pay special attention to new growth, the undersides of leaves, and flower buds, as these are the areas thrips are most likely to inhabit. Look for signs of feeding damage or the insects themselves.
- Species Identification: Understanding which species of thrips are present can be incredibly beneficial. Different species may have varying life cycles, feeding behaviors, and susceptibilities to control measures. Accurate identification can inform more targeted and effective management strategies. Read how to ID thrip species commonly found in greenhouses here.
Strategies used for implementing biocontrol should focus on being proactive rather than reactive. Focusing on the use of natural predators to keep thrip populations in check before they have a chance to reach damaging levels. Three commonly used biological control agents are OriLiv, SwiLiv, and HypoLiv, each offering unique benefits:
- OriLiv: This is a commercial name for a predatory insect, Orius insidiosus. Orius species are known for their effectiveness against thrips because they prey on all moving life stages of the pest. They are aggressive hunters and can significantly reduce thrip populations.
- SwiLiv: Is a predatory mite, Swirskii (Amblyseius swirskii) is another key player in biological control. SwiLiv is adaptable to various environmental conditions and preys on young thrips, as well as other pests like whiteflies and spider mites. Its versatility makes it a popular choice for integrated pest management in greenhouses.
- HypoLiv: This refers to Stratiolaelaps scimitus (formerly known as Hypoaspis miles), a soil-dwelling predatory mite. HypoLiv is particularly effective against the pupal stages of thrips that occur in the soil or substrate. It can also target other pests like fungus gnats, providing a broader spectrum of control.
Insecticides can be a useful tool in managing severe thrips infestations in greenhouses. It's crucial to select targeted sprays and use them conservatively, as thrips are known for quickly developing resistance. These chemicals can also harm beneficial insects, so their use must be balanced with the overall health of the greenhouse ecosystem.
Cultural practices play a crucial role in managing thrips in greenhouses.
Regular removal of plant debris and maintaining good greenhouse hygiene disrupts the breeding cycle of thrips.
Controlling weeds is also vital; by eliminating these potential alternative hosts both inside and around the greenhouse, you reduce habitats and food sources for thrips, aiding in controlling existing populations and preventing new infestations.
Additionally, consistent scouting is key for early detection. Regular inspections for signs of thrips damage or the insects themselves enable timely and effective intervention.
Effective management requires a combination of monitoring, biological control, selective chemical use, and good cultural practices. Collectively, these efforts form a solid foundation for thrip control.