Cassava Lace Bug

📖 Description

Vatiga illudens — the Cassava Lace Bug — is a tingid bug pest of cassava in India, with economic significance centred on the cassava belts of Tamil Nadu (Salem, Namakkal, Dharmapuri, Erode, Cuddalore — India’s largest cassava-growing state), Kerala (Thiruvananthapuram, Kollam, Pathanamthitta, Alappuzha), Andhra Pradesh (Visakhapatnam, Srikakulam, East Godavari), and Northeast India (Nagaland, Mizoram, Meghalaya). India produces ~5 million tonnes of cassava from ~2.5 lakh ha (much of it processed into sago and tapioca — Salem is India’s ‘sago capital’). The pest is native to South America (the native range of cassava) but has spread to all tropical cassava-growing regions of the world through the international movement of cassava planting material — it was first reported in India in the 2010s from Tamil Nadu and Kerala, likely introduced through infested stem cuttings imported for breeding programmes, and has since spread to all major cassava-growing belts. The pest’s biology makes it particularly damaging: (1) eggs are concealed inside leaf tissue with only the operculum visible — appearing as small black dots, easily overlooked; (2) nymphs and adults feed on the underside of leaves — concealed during routine inspection; (3) rapid reproduction — females lay 60–100 eggs and complete a generation in 25–30 days; (4) the pest forms dense colonies — a single leaf can support 100+ individuals; and (5) damage is most severe during the dry season when cassava is already under water stress. The economic impact is significant: heavy infestations can defoliate 30–50% of the canopy, reducing tuber yield by 15–25%. Damage is most severe during the dry season (March–May in Tamil Nadu) when cassava is under water stress — combined pest and drought stress can cause complete defoliation and tuber yield losses of 40–60%. For a typical Tamil Nadu cassava grower cultivating 1 ha (yield 25–30 t/ha at ₹3,000–4,000 per tonne), a severe V. illudens infestation can wipe out ₹15,000–30,000 of annual income. The pest is particularly concerning because it is invasive in India — without natural enemies present in its native South American range, populations can build up unchecked. Management is best achieved through IPM combining inspection of planting material (preventing new infestations), tolerant varieties (Sree Jaya, Sree Vijaya — CTCRI-released varieties), adequate dry-season irrigation (reducing drought-stress susceptibility), yellow sticky trap monitoring, NSKE 5% or azadirachtin foliar sprays during peak oviposition, biological control (Amblyseius swirskii predatory mite releases), intercropping with cowpea or groundnut, and conservation of natural enemies. The Central Tuber Crops Research Institute (ICAR-CTCRI, Thiruvananthapuram) and ICAR-NBAIR (Bangalore) are jointly evaluating classical biocontrol introductions of South American parasitoids (e.g., Erythmelus tingidoiphagus, Anagrus species) to provide long-term control of this invasive pest in Indian cassava.