Gladiolus Thrips

📖 Description

Gladiolus Thrips (Thrips simplex), also called Gladiolus Thrips or Corm Thrips, is a serious sap-sucking pest of gladiolus and other Iridaceae ornamentals across the Indian subcontinent, particularly severe in the major gladiolus-growing belts of West Bengal (Kalimpong, Darjeeling, Kurseong — India’s largest gladiolus-producing region), Uttarakhand (Dehradun, Nainital, Mussoorie), Himachal Pradesh (Shimla, Kullu, Manali, Palampur), Karnataka (Coorg, Chikmagalur), Tamil Nadu (Nilgiris, Kodaikanal), Maharashtra (Mahabaleshwar, Panchgani), Sikkim, Arunachal Pradesh and Meghalaya where India is a significant producer of gladiolus cut-flowers (over 5,000 hectares cultivated across all states, producing over 200 million cut-flowers annually worth over ₹150 crore — gladiolus is one of the top four bulbous ornamental crops in India, grown both for domestic cut-flower markets and for export). The pest is unusual among ornamental pests because (a) it is highly host-specific to gladiolus and a few related Iridaceae (Freesia, Crocosmia, Tritonia) — but this specialisation makes it extremely damaging when present, (b) the thrips colonises the protected interior of flower buds and between corm scales where contact insecticides and natural enemies cannot easily reach — requiring systemic insecticides or hot-water treatment of corms for effective control, (c) the pest is the only known vector of Gladiolus Iris Mosaic Virus (AIMV) and also vectors Tomato Spotted Wilt Virus (TSWV) — making it a dual threat as both a direct sap-sucking pest and a virus vector, (d) the pest is corm-borne — thrips survive between seasons inside the corm scales and reinfest new plantings from infected corms, making hot-water corm treatment the most critical preventive measure, (e) the pest has a very short life cycle (12-20 days) allowing 15-20 overlapping generations per year and rapid population buildup, especially in warm dry conditions, and (f) the pest has developed resistance to most major insecticide classes (organophosphates, pyrethroids, carbamates) in many parts of India due to indiscriminate use on ornamentals. IPM with thrips-free corm certification (most critical preventive measure), hot-water corm treatment at 43°C for 2 hours before storage and before planting (kills thrips inside corm scales — most critical curative measure for corm-borne infestations), blue sticky trap monitoring (thrips preferentially attracted to blue — more effective than yellow), biological control (Amblyseius swirskii predatory mites — highly effective in greenhouses and shade nets; Orius anthocorid bugs — both nymphs and adults consume thrips; conservation of native predators), neem-based sprays, need-based insecticide rotation (Spinosad is most effective — biosynthetic, low toxicity to predators; Fipronil is systemic — effective against thrips inside buds), weed host management, and roguing of virus-infected plants provides effective and sustainable control. The pest is a particular concern for Indian gladiolus growers because (i) gladiolus is a high-value export-oriented cut-flower crop — even slight thrips scarring renders flowers unsaleable for export, (ii) the crop is propagated vegetatively from corms which perpetuates corm-borne thrips and virus infections between seasons, (iii) the crop is grown mostly by small-scale flower farmers with limited access to IPM knowledge and hot-water treatment facilities, and (iv) the crop is often grown in hill regions (Himachal, Uttarakhand, West Bengal hills) where cool humid conditions favour both thrips and the entomopathogenic fungi that control them — making biological control especially viable. Climate change with warmer drier conditions is expanding the pest’s range and severity into previously cool hill regions.