Thrips in Peppers: Damage, Symptoms, and Effective Management

Composed and edited by: Dr. Nagraani Mahaajan, Publication Director, Advanced Training in Plant Breeding, Aurangabad, Maharashtra, India

Thrips: Hosts, Damage, Common Symptoms, and Management in Peppers

Thrips, though tiny at just 1-2 mm long, can have a major impact on the health and productivity of pepper crops. These small insects, with their fringed wings, are more than a nuisance; they are destructive pests that can cause significant yield losses in both bell and chili peppers. Thrips infestations damage plants, reducing both the quantity and quality of the harvest. For farmers, understanding their behavior, the damage they cause, and how to manage them is vital to protect pepper crops and maintain sustainable agricultural practices.

Additionally, thrips are vectors for various plant viruses, making effective management even more essential. Thrips can lead to curled leaves, reduced plant vigor, and, in severe cases, total crop loss. The economic impact on pepper production can be substantial for both small-scale and large-scale farming.

Photo 1: The two chilli plants, side by side—the one on the right hand—show classical leaf curl with upward leaf rolling, which is caused by the thrips, whereas the leaves in the genotype on the left hand are very normal. The thrips that you see on the right side of the slide are Scirtothrips dorsalis, which is called the chili thrips.

In the last 3-4 years, a new invasive species of thrips, commonly called Black thrips, Thrips parvispinus, has been causing havoc in South India on Chilli, Sweet pepper, and cotton. 50-80% damage was observed in Telangana, AP and Karnataka. Furthermore, this species is resistant to most of the insecticides. However, so far, it has not been reported as a vector of any tospovirus.

Understanding Thrips Damage on Peppers

Thrips cause direct damage to pepper plants by feeding on their tissues. This can lead to:

• Upward leaf curling and rolling
• Reduced plant vigor
• Significant yield loss, especially in chili peppers, where damage can range from 20% to total crop loss if not managed properly

Thrips can cause severe damage to bell peppers too, especially when the weather is conducive. Bell peppers are more susceptible to thrips than chili peppers due to their secondary evolution in Europe, where thrips pressure is relatively lower. Thrips damage in bell peppers can lead to both quantitative and qualitative yield loss, as fruits are scarred by thrips damage.

Photo 2: Thrips damage occurring at the young stage on a bell pepper crop

Common Symptoms

The presence of thrips in pepper plants can be identified by several symptoms:

• Leaf Curling: Leaves may curl upwards, a common sign in chili plants.
• Fringed Wings: Thrips have unique fringed wings, visible under magnification.
• Deep Punctures and Scratches: On the underside of leaves, leading to reddish-brown discoloration, while the upper side appears yellowish.

Damage by black thrips can be similar but the damage is more on the lower surface of leaves and black adult thrips tend to congregate on flowers. Further, such flowers dry and wither.

Photo 3: Please take note of the following information: A zero rating indicates a healthy crop. A rating of one shows slight crinkling of terminal leaves, while a rating of two shows mild crinkling of the bottom leaves. A rating of three involves upward curling of the top leaves. Ratings of four and five signify more severe damage. Interventions at stages one and two can prevent significant yield loss in chilli peppers.

Rating for thrips damage is efficient and quick. Normally the first spray should start before the rating reaches 2. Further sprays can be given 10-15 days after observing the plants especially the top leaves and rainfall pattern. In polyhouse cultivation, it is advisable to always keep the damage below 2 and care must be taken to avoid damage on fruits.

Black Thrips (Thrips parvispinus)

Black thrips have two characteristic features:

1. They congregate on floral petals in significant numbers (10 to 75).
2. Nymphs are concentrated on the lower surface of leaves, while adults feed on both surfaces.

Black thrips are often noticed after heavy rain, but rainfall does not significantly influence their multiplication. They occupy niche areas where other thrips, like Scirtothrips dorsalis, are less prevalent post-rains.

Photo 4: Thrips parvispinus, as you can see, is typically blackish and very much present on the petals.

Managing Thrips in Pepper Crops

Managing thrips in pepper plants involves several strategies:

1. Nursery: Raising the nursery in an insect-proof net house and not in the open nursery. Take adequate precautions to control thrips on Seedlings.
2. Prior to transplanting, dip the seedlings in a recommended insecticide solution.

3. Cultural Practices: Regular monitoring and maintaining plant health can reduce thrips infestations. Recommended practices include:

• Following appropriate spacing for the cultivar to avoid closer spacing.
• Erecting white or blue sticky traps at 65–75 traps/ha.
• To reduce thrips pupation in the soil, drip irrigation and mulching with silver-colored polythene sheets of 25–30 micron thickness are used.

4. Biological Control: Introducing natural predators of thrips can help keep their population in check.

5. Chemical Control: Insecticides can be used, but thrips often develop resistance. It’s crucial to rotate insecticides and use them judiciously. Recommended insecticides include:

• Spinosad 45% SC @ 0.25 ml/l
• Spirotetramat 15.31% OD @ 0.75 ml/l
• Dimethoate 30% EC @ 2 ml/l + Lambda-cyhalothrin 5% EC @ 1 ml/l
• Emamectin Benzoate 1.50% + Fipronil 3.50% SC @ 1.25 ml/l
• Diafenthiuron 47% + Bifenthrin 9.40% w/w SC @ 1.25 ml/l

Drenching with chemicals like chlorpyrifos 20 EC @ 5 ml/L or spreading neem cake on beds can help manage thrips. Soil application of entomopathogenic nematodes (EPNs) like Steinernema carpocapsae or Heterorhabditis indica @ 5 kg/acre is also effective.

6. Host Plant Resistance: Breeding and using resistant plant varieties can significantly reduce thrips damage.

The Role of Crop Wild Relatives (CWR) in Pest Management

Crop wild relatives (CWR) are wild species related to cultivated crops. They are valuable for breeding programs because they often possess traits like pest resistance. Incorporating genes from CWR into cultivated crops can enhance resistance to thrips and other pests, contributing to sustainable agriculture.

Thrips and Virus Transmission

Thrips are not only pests but also vectors for tospoviruses, which can inflict severe damage on crops like pepper, tomato, onion, watermelon, groundnut, and chrysanthemum. Their long evolutionary relationship with viruses makes understanding this interaction essential for developing resistant varieties. For instance, Lycopersicum hirsutum (now S. hybrochitiss) provides resistance to insects and leaf curl virus in tomatoes yet is susceptible to spotted wilt virus. Major tospoviruses include groundnut bud necrosis virus, watermelon bud necrosis virus, and tomato GBNV and TSWV, among others. In India, significant thrips species transmitting tospoviruses include Thrips tabaci, Thrips palmi, Scirtothrips dorsalis, and Frankliniella occidentalis. Some thrips facilitate virus transmission via pollen, such as the sunflower bud necrosis Ilarvirus. Tospovirus symptoms often manifest as characteristic ring spots and may lead to plant death. Surviving plants, like tomatoes and peppers, may exhibit concentric ring spots and uneven ripening. Tospoviruses can be mechanically
transmitted via infected sap, with nymphs acquiring the virus and adults transmitting it. This replication within thrips raises concerns about importing flower crops without quarantine, as it can introduce new tospoviruses.

Case Studies and Research Insights on Thrips and Virus Transmission

1. TSWV and GBNV Studies: Studies at IIHR have shown the classical differences in symptoms between Tomato Spotted Wilt Virus (TSWV) and Groundnut Bud Necrosis Virus (GBNV) in tomatoes. Early detection and reporting of new virus diseases are crucial to prevent widespread damage.
2. Transmission Studies: Research has demonstrated that thrips acquire tospoviruses only during their larval stage. After emerging from the pseudo-pupal stage, adults can transmit the virus to new host plants within minutes of probing.
3. Molecular Markers: The development of species-specific molecular markers has facilitated the identification of thrips species and their role in virus transmission. This is essential for accurate diagnosis and management.
4. Vector Efficiency: Studies have shown that the efficiency of thrips as vectors varies. For instance, Indian populations of Thrips palmi are more efficient in transmitting the Watermelon Bud Necrosis Virus than other global populations.
5. Genome Organization of Tospovirus: Tospoviruses have a tripartite genome with large, medium, and small RNA segments. Understanding the genome organization and the role of non-structural proteins in overcoming host resistance is crucial for developing durable resistance in pepper plants.

Integrated Pest Management (IPM) Strategies for Thrips

1. Early Detection and Monitoring: Regularly inspect pepper plants for signs of thrips and their damage. Use sticky traps to monitor thrips populations.
2. Cultural Controls: Implement crop rotation and remove plant debris to reduce thrips habitats. Maintain proper plant spacing to improve air circulation and reduce humidity.
3. Biological Controls: Utilize natural predators such as predatory mites and lacewings to control thrips populations.
4. Chemical Controls: Apply insecticides judiciously and rotate different classes of insecticides to prevent resistance development.
5. Physical Controls: Use reflective mulches to deter thrips and install insect-proof nets in greenhouses.
6. Seedling Management: Raise seedlings in a protected nursery and manage thrips there. Dip seedlings in insecticide before transplanting.
7. Remove Infected Plants: Eradicate plants infected with tospoviruses.
8. Design Considerations: In protected cultivation, design elements like net houses, double doors, and hygiene practices are critical.

Research and Development Needs in Thrips Management

1. Understanding Thrips-Plant Interactions: Further research is needed to understand the interactions between thrips and pepper plants, including the mechanisms of resistance.
2. Breeding for Resistance: Develop pepper varieties with enhanced resistance to thrips and tospoviruses through traditional breeding and biotechnological approaches.
3. Quarantine and Biosecurity: Strengthen quarantine measures to prevent the introduction and spread of invasive thrips species.
4. Extension Services: Provide training and resources to farmers on thrips management practices and the importance of early detection and intervention.

Conclusion: Effective Thrips Management for Sustainable Pepper Production

Thrips are a major pest affecting pepper crops. Effective management requires a combination of cultural, biological, and chemical strategies, along with the use of resistant plant varieties. Understanding and utilizing the role of crop wild relatives can further enhance pest management efforts. Additionally, studying the transmission of viruses by thrips is essential for developing comprehensive management strategies.

References

kr, Latha & Kumar, N. & Swamy, H & Asokan, Ramasamy & Ranganath, Harindranath & Mahmood, Riaz. (2020). Molecular identification and diversity of chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) employing ITS2 marker.

kr, Latha & Kumar, N. & Swamy, Mahadeva & Mahmood, Riaz. (2020). A Novel Rearing Technique for the Chilli Thrips Scirtothrips dorsalis Hood (Thysanoptera: Thripidae).

Krishna Kumar, N.K., Aradya, M., Deshpande, A.A. et al. Initial screening of chili and sweet pepper germplasm for resistance to chili thrips, Scirtothrips dorsalis Hood. Euphytica 89, 319–324 (1996). https://doi.org/10.1007/BF00022288

Further reading

Growing Peppers for Profit – Pepper and Chilies Farming

Growing Sweet and Hot Chili Peppers in my Backyard

Integrated Pest & Disease Management in Greenhouses: A Comprehensive Guide

Integrated Pest Management (IPM): Sustainable Solutions for Healthy Crops and Ecosystems

10 Advanced Tips for Effective Crop Monitoring and Early Pest and Pathogen Detection

Management Strategies to Avoid Insecticide Resistance

An Innovative Approach to Protect Tomatoes and Cucurbits from Emerging Viral Epidemics

Integrated Pest (Disease & Weed) Management (IPM): Principles, Practices and Advantages

Important Beneficial Insects as Natural Enemies of Crop Pests