Biological control in Indonesian oil palm potentially enhanced by landscape context

Oil palm plantation expansion is occurring at a rapid pace. However, substantial yield losses from pest attacks are becoming major threats to the oil palm industry, while the potential role of conservation biological control, a sustainable and environmentally friendly solution for pest control, is still largely unknown. The type of vegetation surrounding oil palm plantations is likely to influence pest predation, and we tested this in Indonesia (Sumatra), the world's largest palm oil producer. We studied six different vegetation types adjacent to oil palm plantations: another oil palm plantation (control), weedy oil palm, weedy rubber, scrub, jungle rubber, and secondary forest. Each border type was replicated eight times. We quantified predation rates and predator occurrences using duminy caterpillars and mealworms 20 m inside of the adjacent vegetation (OUT 20) as well as 20 m (IN 20) and 50 (IN 50) m inside the oil palm plantation. Ants and bush crickets were the most prominent predators in the plantations, whereas birds, bats, monkeys, beetles, and molluscs played a minor role. Mean percentage of ant and cricket predation rate in control border OUT 20 were 16.39% and 7.16% respectively, IN 20 were 16.03% and 6.1%, and IN 50 were 14.47% and 7.48%, while for other borders other than control, mean percentages OUT 20 m were 28.90% and 12.26% respectively, IN 20 m were 26.61% and 12.40%, and IN 50 m were 22.93% and 10.58%. Predation rates were 70% higher in non-oil palm habitat, indicating the need for improved vegetation diversification inside plantations. Overall predation rates in oil palm decreased slightly but significantly with distance to the border. Our results suggest that maintaining non-oil palm vegetation in the areas adjacent to plantations and promoting weedy strips within the plantations are potentially effective management tools for conserving and developing biological control in oil palm in the future. (C) 2016 Elsevier B.V. All rights reserved.