Parasitoid Population in Beneficial Plant Areas of Oil Palm (Elaeis guineensis Jacq.) Plantations at Torgamba Plantation

Abstract

Bagworms (Lepidoptera: Psychidae) are among the most damaging defoliating pests in oil palm plantations, and parasitoids are key natural enemies for their biological control. Beneficial (flowering) plants are expected to enhance parasitoid activity by providing nectar, pollen, and shelter that support parasitoid survival and reproduction. This study assessed the effect of beneficial plants on bagworm populations and the associated parasitoid activity at Torgamba Plantation, South Labuhanbatu Regency, North Sumatra, Indonesia. A survey method was applied to two observation blocks a beneficial-plant block and a control block without beneficial plants each comprising 25 sample palms, observed monthly from October to December 2025. Data were analyzed using descriptive statistics and an independent-samples t-test at the 5% significance level. The mean bagworm population was markedly lower in the beneficial-plant block (0.73 individuals per palm) than in the control block (4.25 individuals per palm), and the difference was statistically significant (p < 0.05). The higher parasitoid activity observed in the beneficial-plant block coincided with this reduction, indicating that beneficial plants provide suitable habitat for parasitoids and thereby strengthen biological control. Beneficial plants are therefore recommended as a component of sustainable, environmentally friendly pest management in oil palm plantations.