Palmarosa Shoot Fly

📖 Description

Palmarosa shoot fly, Atherigona naqvii — named after the Indian dipterist M.S. Naqvi who first described it from palmarosa in the 1970s — is the major Dipteran pest of palmarosa (Cymbopogon martinii) cultivation in India. Adult flies emerge in the morning, mate, and females lay 30–60 eggs singly on the undersides of young palmarosa leaves and inside the leaf whorl. The creamy-white legless maggots that hatch in 2–3 days immediately tunnel downward into the central shoot, feeding on the developing tissue. The larvae feed for 7–10 days, moulting 3 times, then pupate inside the dead shoot or in the soil at the base of the plant. Adult flies emerge 7–10 days later. Total lifecycle is 18–25 days at 25–28 °C, allowing 8–10 overlapping generations per year. The most diagnostic field sign is the ‘deadheart’ symptom — the central shoot dries up and turns brown, and can be easily pulled out from the whorl. Heavy infestations can destroy 30–60% of young shoots in a palmarosa planting, particularly during the establishment phase (3–6 months after planting), when plants are most vulnerable. Affected plants produce side tillers, but these are typically weaker and have lower oil content. Repeated infestation can stunt plant growth and delay harvest by 4–8 weeks. Yield losses of 20–40% in herbage and 15–30% in essential-oil content have been reported from Madhya Pradesh and Andhra Pradesh, with annual economic losses estimated at ₹50–80 crore. The pest is particularly damaging because palmarosa is a slow-growing perennial that takes 4–6 months to establish, and shoot-fly damage during the establishment phase can set back the planting by a full season. The pest is closely related to the sorghum shoot fly (Atherigona soccata) — a major pest of sorghum and pearl millet — and the two species share many biological features, including the use of chemical cues (kairomones) to locate host plants. Atherigona naqvii is dispersed primarily by adult flight — flies can travel 1–2 km to locate new plantings — and by infested planting material (slips). Integrated management combines systemic insecticides (carbofuran, imidacloprid) at planting, neem oil foliar sprays during the establishment phase, fish-meal traps for adult monitoring and capture, hand-removal and burning of ‘deadheart’ shoots, and planting of trap crops of resistant sorghum around the perimeter. CIMAP (Central Institute of Medicinal and Aromatic Plants, Lucknow) has developed IPM packages for palmarosa shoot fly that have been adopted by aromatic-grass growers in Madhya Pradesh, Andhra Pradesh, and Uttar Pradesh.