Shisham Gall Midge
Trioza obsoleta
📖 Description
Trioza obsoleta is a psyllid pest of shisham (Dalbergia sissoo) in India. Shisham is one of India’s most important timber trees — Indian shisham forests cover approximately 1.5 million ha, with plantations established on railway land, canal banks, farmland boundaries, and as an agroforestry intercrop. Shisham timber is the traditional material for Indian furniture and is sold at ₹1,500–3,000 per cubic foot. The species is under pressure from ‘shisham dieback disease’ (a Phytophthora-related decline) and the gall midge is a chronic secondary pest that exacerbates stress on weakened trees. Outbreaks are most severe in young plantations (1–3 years old) and in water-stressed trees. The gall midge is multivoltine, with 5–6 overlapping generations per year in tropical conditions. The pit gall induced by nymphal feeding is a complex plant-insect interaction — the nymph’s salivary secretions induce localised cell proliferation that forms a protective pit around the feeding insect.
⚠️ Symptoms to watch for
- Nymphs feed on leaf tissue, inducing characteristic deep pit galls on the underside of leaves with corresponding raised bumps on the upper surface
- heavily infested leaves show dozens of galls each containing a single nymph
- severe infestation causes premature leaf drop, reduced growth, and aesthetic damage to ornamental plantings
- in young plantations (1–3 years), severe defoliation can stunt growth for one season.
- The galls are diagnostic — no other shisham pest produces similar pit galls.
🩹 Treatment
- Spray imidacloprid 17.8 SL at 0.3 ml/L or thiamethoxam 25 WG at 0.2 g/L at 30-day intervals during the active season (April–October).
- Apply dimethoate 30 EC at 1 ml/L as a foliar spray.
- Use yellow sticky traps at 4 per ha to monitor adult activity and mass-trap.
- Prune and burn heavily infested leaves from young trees — practical for nurseries and small plantings.
🌿 Organic treatments
- Spray neem oil (1 % Azadirachtin) at 5 ml/L plus sticker at 14-day intervals.
- Apply fish oil rosin soap at 25 g/L as a foliar spray.
- Release predatory ladybirds (Coccinella transversalis) at 5,000 per ha.
- Encourage predatory bugs (Anthocoridae) and lacewings (Chrysoperla) by maintaining ground vegetation cover.
- Prune and burn heavily infested leaves from young trees.
🧪 Chemical treatments
- Imidacloprid 17.8 SL (0.3 ml/L), thiamethoxam 25 WG (0.2 g/L), or dimethoate 30 EC (1 ml/L).
- Apply as a foliar spray at 30-day intervals during the active season (April–October).
- Rotate chemical classes to prevent resistance development.
🛡️ Prevention
- Plant shisham at recommended spacing (3 m × 3 m for timber plantations) to ensure vigorous growth and adequate airflow.
- Maintain ground vegetation cover to encourage natural enemies.
- Avoid excessive nitrogen fertilisation which produces soft succulent growth favoured by ovipositing females.
- Inspect plantations weekly during the active season and prune infested branches promptly.
🪴 Affected plants
- Shisham / Indian rosewood (Dalbergia sissoo) is the primary host
- also recorded on Dalbergia latifolia (Indian rosewood) and occasionally on Pongamia pinnata in mixed plantings.
- The species is a chronic pest of shisham plantations and agroforestry systems throughout India.
🦋 Natural predators
- Predatory ladybirds (Coccinella transversalis, Menochilus sexmaculatus), predatory bugs (Anthocoridae — Orius spp.), lacewing larvae (Chrysoperla zastrowi sillemi), and spiders (Salticidae, Thomisidae).
- Parasitoid wasps (Tamarixia spp., Encarsia spp.) attack nymphs inside galls.
🌱 Host plants
- Dalbergia sissoo (shisham — primary host)
- Dalbergia latifolia (Indian rosewood)
- Pongamia pinnata (karanj — occasional).
🔄 Lifecycle
- Egg (5–7 days, laid on leaf underside) → Nymph (20–30 days, 5 instars, inside pit gall) → Adult (15–25 days).
- Multivoltine — 5–6 overlapping generations per year in tropical India; 3–4 generations per year in subtropical north India.
📅 Season
- Active throughout the year in tropical India; peak activity April–June (pre-monsoon new flush) and September–November (post-monsoon flush).
- Lowest activity in cold winter (December–January) in north India.
🔎 Appearance
- Adult is a small, delicate psyllid (jumping plant louse) with transparent wings held roof-like over the body at rest; body is yellowish-green with dark eyes; legs are long and adapted for jumping.
- Nymphs are flattened, oval, yellowish-orange, and live inside characteristic pit galls on the underside of leaves; mature nymphs reach 2 mm and have conspicuous waxy filament tufts at the posterior end.
💥 Damage level
- Moderate
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- Indian shisham tract (Punjab — Hoshiarpur, Ropar; Haryana — Kurukshetra, Karnal; Uttar Pradesh — Saharanpur, Bijnor; Uttarakhand — Dehradun, Haridwar; Bihar — West Champaran, East Champaran; West Bengal — Cooch Behar, Jalpaiguri; Assam — Darrang, Sonitpur).
- Also reported from Pakistan, Nepal, and Bangladesh.
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