Silver Oak Defoliator

📖 Description

Antheraea mylitta — the Tasar Silkworm Moth — is a wild saturniid moth best known as the source of tropical Tasar silk, but in India’s Western Ghats coffee belt (Kodagu, Chikmagalur, Hassan, Wayanad) it is also a periodic defoliator of Silver Oak (Grevillea robusta), the dominant shade tree of Arabica coffee plantations. The moth completes one generation in 65–80 days, with peak adult emergence and oviposition in October–November, just after the southwest monsoon retreats. Females lay 150–250 eggs in clusters on the underside of Silver Oak leaflets; the larvae — initially gregarious, later solitary — feed ravenously for 35–45 days, moulting five times. A single mature larva can consume 80–100 sq. cm of leaf per day, and a heavy infestation can strip 60–90% of a Silver Oak canopy within 3–4 weeks. The economic impact on coffee is indirect but real: defoliated shade trees fail to provide the 40–60% shade that Arabica requires for optimal berry set, bean density, and beverage quality, exposing coffee bushes to sun-scorch, premature cherry drop, and reduced acidity in the cup. Heavily defoliated Silver Oaks also slow in timber growth — Silver Oak is harvested at 25–30 years for furniture-grade timber that fetches ₹1,500–2,500 per cubic foot, providing a meaningful income supplement to smallholder coffee growers. Beyond the direct defoliation, the tough brown cocoons spun by mature larvae dangle from shade-tree foliage and frequently drop into harvest baskets during the September–February coffee harvest, contaminating cherry coffee and requiring additional hand-sorting. The pest is naturally cyclical — outbreaks occur every 5–8 years in the Western Ghats, typically following a year of above-average monsoon rainfall that promotes lush Silver Oak flush. Between outbreaks, the pest persists at low background densities, maintained by natural enemies including Trichogramma chilonis (egg parasitoid), Telenomus dapulus (egg parasitoid), and Apanteles mylitta (larval braconid parasitoid) — the same biocontrol agents used in commercial Tasar silk culture. Integrated management in coffee combines monitoring (binoculars, light traps), conservation of natural enemies (avoiding broad-spectrum insecticides), targeted Bt application during early instars, and manual cocoon removal — the Coffee Board of India’s IPM package specifically lists Antheraea mylitta as a ‘shade tree pest to be tolerated at low densities and managed only at outbreak densities above 5 larvae per Silver Oak tree’.