Western Flower Thrips

Challenges in Thrips Control

The difficulties encountered in controlling Thrips spp. highlight the need for effective and continuous pest management strategies. Studies and field observations have shown that Thrips populations can develop resistance even to certain unauthorized plant protection products. This clearly demonstrates that relying solely on chemical control methods is not a sustainable long-term solution.

Thrips spp. was first identified in Türkiye in 1993 on greenhouse-grown carnations in Antalya. The pest has an extremely broad host range. In addition to ornamental plants such as carnations and roses, it can cause significant economic damage to tomatoes, peppers, eggplants, cucumbers, melons, watermelons, strawberries, spinach, okra, and many fruit crops.

Adult thrips are approximately 1 mm in length, yellowish in color, and highly mobile. Both adults and larvae are commonly found on the underside of leaves. In warm regions, they continue reproducing as long as suitable host plants are available. Depending on environmental conditions, they can produce 3–6 generations per year, and in some cases up to 10 generations annually.

How Does Thrips spp. Damage Plants?

Thrips populations have become increasingly difficult to control and can cause severe damage to crops. Adults and nymphs feed by sucking plant sap from leaves, petals, flowers, flower buds, stems, and fruits.

Affected leaves gradually develop a whitish or silvery appearance. Feeding damage on fruits reduces market quality and value. In addition, feeding wounds create entry points for bacterial, fungal, and viral pathogens. Adult thrips are capable of flying considerable distances, making them efficient vectors for the spread of plant viruses and diseases.

Climate Change Has Altered Pest Biology

The negative impacts of climate change on crop production, combined with rising temperatures, have created increasingly favorable conditions for many agricultural pests. As a result, pest management has become more challenging.

Excessive and indiscriminate chemical applications against pests such as Thrips spp. further complicate population control by accelerating resistance development and disrupting integrated pest management programs.

Why Is Chemical Control of Thrips Difficult?

Several biological characteristics reduce the effectiveness of chemical treatments:

• Eggs are deposited inside plant tissues.
• Adults and larvae hide within flower structures.
• Pre-pupal and pupal stages occur in the soil.
• The pest develops resistance rapidly.
• It completes its life cycle within a relatively short period.

These factors significantly limit the success of chemical control strategies.

Integrated Management Is Becoming Increasingly Important

Due to the limitations of chemical control, integrated pest management (IPM) approaches have gained increasing importance in recent years. These strategies aim to improve crop yield and quality while minimizing pesticide residues.

Thrips Control with Entomopathogenic Nematodes (EPNs)

Entomopathogenic Nematodes (EPNs) have become widely used in the biological control of numerous insect pests. Their effectiveness against pests that spend part of their life cycle in the soil has contributed to their growing popularity.

EPNs are obligate endoparasitic nematodes that infect insects, causing disease and death while completing their life cycle within the host insect. These nematodes carry approximately 200 symbiotic bacterial cells within a specialized structure in their bodies. The bacteria and nematodes work together in a mutually beneficial relationship.

Why Are EPNs Effective Against Thrips?

The life cycle of Thrips spp. consists of:

1. Egg stage
2. First larval stage
3. Second larval stage
4. Pre-pupal stage (in soil)
5. Pupal stage (in soil)
6. Adult stage

Approximately 95% of the pre-pupal and pupal stages occur in the soil at depths of 1.5–2 cm. This period accounts for nearly one-third of the pest's total life cycle.

The pre-pupal and pupal stages are ideal targets for EPN applications because the insects remain relatively immobile and vulnerable for 2–6 days. By targeting these soil-dwelling stages, EPNs help suppress future adult populations and reduce the pest's ability to reproduce and spread diseases.

How Do EPNs Work?

After application to the soil, entomopathogenic nematodes enter pre-pupal and pupal thrips through natural openings such as the mouth and anus. Once inside, they release their symbiotic bacteria into the digestive system or body cavity of the host.

Following bacterial release, the host insect typically dies within 24–48 hours. The insect cadaver becomes filled with nutrient-rich fluids that serve as a food source for both the nematodes and the bacteria. They continue reproducing within the dead insect until new infective juvenile nematodes emerge and seek additional hosts.

Integrated Management Strategy Against Thrips spp.

When only chemical control is used, the soil-dwelling stages of Thrips are often overlooked. Under favorable temperature and humidity conditions, populations can quickly rebound.

Furthermore, repeated use of chemical pesticides has accelerated resistance development, making population management increasingly difficult. The high cost and complexity of developing new active ingredients, combined with the declining number of registered insecticides and increasing resistance to existing products, have intensified the challenge.

An effective integrated pest management program may include:

• Entomopathogenic nematodes and other biological control agents
• Traps and biotechnical control methods
• Cultural control practices
• Registered chemical pesticides when necessary

This comprehensive approach targets multiple life stages of the pest and helps maintain populations below the economic damage threshold.

Benefits of EPNs

• Leave no harmful residues.
• Provide preventive control before severe infestations develop.
• Reduce dependence on chemical pesticides.
• Help slow the development of pesticide resistance.
• Do not induce resistance in pest populations.
• Easy to apply.
• Compatible with drip irrigation systems and spray applications.
• Compatible with many chemical pesticides.
• Safe for users, consumers, beneficial organisms, and the environment.
• Derived from natural biological sources.

When applied correctly and under suitable conditions, EPNs can play a highly effective role in maintaining Thrips populations under control as part of a sustainable integrated pest management program.

Source: Agricultural Engineer Görkem Ateş, Bioglobal Inc. (Bioglobal A.Ş.)