Local and Landscape Management of Biological Pest Control in Oil Palm Plantations

Oil palm is the highest yielding vegetable oil crop per unit area and plantations expand at a rapid pace. Large-scale expansion of oil palm plantations, transformed from natural habitat, results in huge biodiversity losses. Biodiversity loss affects ecosystem services such as pest control, pollination and soil processes. We present a review of the pests, diseases and biocontrol in oil palm plantations, the influence of management practices and recommendations for developing sustainable pest and disease management through conservation biological control. We systematically reviewed the literature using the ISI Web of Science, Ebscohost and Google Scholar. In addition, we investigated the effects of six types of boundaries of oil palm plantations (another oil palm plantation (control), weedy oil palm, weedy rubber, scrub, jungle rubber, and secondary forest) and the distance from the adjacent boundary vegetation on predation of oil palm caterpillar pests. Finally, by using agent-based models (NetLogo), we extend the previous study on the enhancement of predation by adjacent vegetation by simulating the role of border type, plantation size and plantation shape. In the review, whilst direct studies on the effects of the local and landscape managements on pests, diseases and biocontrol are missing, information from published studies can be used to estimate the relative important of management type. For instance, pesticide applications tend to produce problems such as damage on non-target organisms and pest resistance. Fertilizer application accompanied with burying oil-palm waste as compost around oil palms, and together with Trichoderma spp., appears to be the best method for promoting biocontrol of diseases. Studies on vegetation surrounding oil palm plantations focus on butterflies and wild pigs, whereas pest, disease, and biocontrol organisms have not been studied yet. Oil palm understory has a positive influence, but more likely if specific flowering plants. The field investigation revealed that ants and bush crickets were the most prominent predators of caterpillar pest in the plantations. Predation rates in oil palm decreased slightly but significantly with distance to the border, indicating the need for improved vegetation diversification inside plantations. Further tests with simulation models show that complex vegetation surrounding the plantation can enhance pest predation levels, even doubling predation rates inside the plantation. Increasing plantation size led to considerable decrease in pest predation, while changing the plantation geometry in a way that perimeter-area ratios increase can compensate the loss of predation. In conclusion, there is a lack of research how pests, diseases and biocontrol are determined by local management. Further, we recommend a broader perspective, considering also landscape management and its potential for biocontrol conservation in future studies