The Outbreak of Tussock Caterpillar, Dasychira inclusa Walker (Lepidoptera: Eribidae) in Two Mature Oil Palm Estates

Oil palm plantations are essential for global vegetable oil production but face significant challenges due to pest infestations, particularly by leaf-eating insects. The tussock caterpillar (Dasychira inclusa), historically not considered a prevalent threat, has emerged as a significant concern in recent observations at IOI Estates. This study investigates the recent outbreak of the tussock caterpillar, focussing on species identification, lifecycle, outbreak dynamics, and control measures. Field observations and census data from Swee Lam Estate, Johor and Detas Estate, Pahang revealed significant fluctuations in larvae populations, with a peak of 110.80±23.70 live larvae per frond at Swee Lam Estate. Field observations confirmed severe defoliation of oil palm leaflets and the presence of tussock caterpillar eggs and cocoons at frond butts/frond bases. Newly emerged larvae displayed ballooning behaviour, dispersing to neighbouring trees and consuming healthy leaflets for growth. The reproductive cycle of D. inclusa was documented, with egg clusters averaging 320.2±88.3 eggs and an incubation period of eight to nine days. Although predation by Sycanus dichotomus, a released biological control agent, significantly impacted tussock caterpillar populations by 16.67±6.09 (T=2.74, p=0.03), it could not fully suppress the rapid emergence of new larvae. Two types of insecticides were also evaluated, with bio-pesticides containing Bacillus thuringiensis subsp kurstaki being more cost-effective (RM45.99/ha) compared to acephate 97 percent water dispersible granules product (RM73.81/ha). Integrated pest management strategies are recommended to mitigate tussock caterpillar outbreaks and preserve oil palm yields. Keywords: Oil palm, tussock caterpillar, Dasychira inclusa, outbreaks, population dynamics, integrated pest management.