Thrips parvispinus, commonly known as black thrips, is an invasive pest species originating from Southeast Asia that has significant implications for agriculture and horticulture. As a member of the "Thrips orientalis group," it infests a wide variety of crops, including chilli, melon, cucumber, brinjal, and ornamental plants. Its small size and cryptic behavior make management challenging, and it has quarantine importance due to its global distribution, spanning Thailand, Australia, Europe, and beyond. This blog highlights key biological and ecological characteristics of T. parvispinus and outlines integrated pest management (IPM) strategies to combat this pest.

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Key Biological Characteristics of T. parvispinus

1. Morphology:

   • Females: Dark brown bodies with lighter-colored heads and thoraxes.
   • Males: Light brown and smaller than females.

2. Life Cycle:

   • Completes its life cycle in 13–14 days under greenhouse conditions.
   • Development stages: Egg, two instar nymphs, prepupa, pupa, and adult.
   • Females live ~9 days, laying ~15 eggs; males live ~6 days.

3. Feeding and Damage:

   • Both adults and larvae feed by rasping and sucking plant sap.
   • Causes damage to leaves, flowers, and fruits, leading to stunted growth, reduced fruit set, and flower drop.
   • Symptoms include distorted leaves, necrotic patches, and reduced plant productivity.

4. Host Range:

   • Infests beans, eggplant, papaya, pepper, potato, shallot, and strawberry.
   • Found in ornamentals like gerberas, citrus, and gardenias in greenhouses.

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Damage and Economic Impact

• On Chilli Crops: Infestations were reported on over 0.4 million hectares in Andhra Pradesh and Telangana, India, with yield losses between 10%–30%.
• Visual Symptoms:
  • Leaves: Yellow streaks, reddish-brown undersides, and deep scratches.
  • Flowers: Brownish streaks on petals, leading to wilting and reduced fruit production.
  
  

  Biological and Developmental Traits

  1. Feeding Behavior: Thrips parvispinus feeds on plant sap and pollen, which enhances its reproductive success.

     • Notable study: Feeding on pollen was observed (J. Pijnakker, unpublished data).

  2. Reproductive Characteristics:

     • Sex Ratio: Female dominance with a 3:1 ratio compared to males (Hutasoit et al., 2019).
     • Reproduction: Sexual reproduction with temperature-dependent fecundity:
       • 50 eggs/female at 20°C
       • 69 eggs/female at 25°C
       • 56 eggs/female at 30°C (Murai et al., 2010).

  3. Development Time: Varies with temperature and host plant:

     • Mean generation times:
       • 37.6 days at 20°C
       • 24.8 days at 25°C
       • 18.8 days at 30°C (Murai et al., 2010).
     • Stages on chilli peppers (Hutasoit et al., 2017):
       • Eggs: 4.79 days
       • Nymphal instars: 1.36 + 3.54 days
       • Prepupa: 1.08 days
       • Pupa: 1.96 days

  4. Lifespan and Reproductive Output:

     • Female lifespan: 8.55 days
     • Male lifespan: 6 days
     • Fecundity: ~15 eggs per female
     • A single female produces an average of 5.71 offspring in her lifetime.

  5. Population Dynamics:

     • Intrinsic rate of increase:
       • 0.18/day at 20°C
       • 0.24/day at 25°C
       • 0.37/day at 30°C (Murai et al., 2010).
     • Doubling time: 4.57 days (Hutasoit et al., 2017).

  Flight Activity

  • Thrips parvispinus demonstrates higher flight activity in greenhouse environments, aiding its spread and infestation.

  Implications for Management

  Understanding the biology, reproduction, and environmental adaptability of T. parvispinus is essential for developing effective pest management strategies, especially in controlled environments like greenhouses. Monitoring temperature and employing integrated pest management (IPM) approaches can help mitigate its impact on crops.

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Integrated Pest Management (IPM) Strategies

1. Cultural Practices:

   • Maintain clean fields and weed-free borders to eliminate alternate hosts.
   • Practice summer ploughing to disrupt resting stages.
   • Use resistant or short-duration crop varieties to avoid peak infestation.

2. Organic Soil Amendments:

   • Apply farmyard manure or compost enriched with Metarhizium anisopliae or Pseudomonas fluorescens.
   • Use vermicompost (500 kg/acre) and neem cake (200 kg/acre) for soil enrichment.

3. Physical and Biological Controls:

   • Employ silver-colored polythene mulch to prevent pupation in the soil.
   • Intercrop chilli with maize/sorghum or cowpea to encourage natural predators.
   • Set up blue,yellow, white sticky traps (25–30 per acre) for monitoring and mass trapping.

4. Botanical and Microbial Pesticides:

   • Use Neem Oil (3%) or Pongamia Oil (3 ml/L) for botanical control.
   • Apply microbial pesticides:
     • Beauveria bassiana at 4 g or ml/L (spore load: 1x10⁸ cfu/g or ml).
     • Pseudomonas fluorescence at 20 g/L.
     • Bacillus albus at 20 g/L
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5. Minimized Chemical Usage:

   • Limit chemical sprays to preserve beneficial insects and maintain ecological balance.

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Additional Observations on Weed Hosts of Thrips

Thrips parvispinus has been found infesting the flowers of several weed species commonly present in chilli fields. These include:

• Parthenium sp.
• Amaranthus sp.
• Axonopus sp.
• Ageratum sp.
• Alternanthera sp.
• Thunbergia sp.

Additionally, the foliage of neem and pongamia trees bordering chilli fields has also been observed to harbor thrips populations.

Implications:

1. Alternate Hosts: These weeds and border plants serve as alternative hosts, sustaining thrips populations even in the absence of the chilli crop.
2. Management Strategy:
   • Ensure weed control within and around chilli fields to minimize thrips infestation.
   • Monitor neem and pongamia foliage for thrips and take appropriate action if infestation is observed.
   • Employ integrated pest management (IPM) practices to disrupt thrips life cycles effectively.

Understanding these host relationships is vital for effective management and to reduce the impact of thrips on chilli crops.

The invasive Thrips parvispinus presents a significant challenge to global agriculture due to its wide host range and ability to cause severe economic losses. Adopting an integrated approach combining cultural, biological, and minimal chemical control measures is critical for managing this pest effectively. Collaboration between farmers, researchers, and policymakers is essential to mitigate its impact and safeguard crop production.