Non-linear effects of pesticide application on biodiversity-driven ecosystem services and disservices in a cacao agroecosystem: A modeling study

Abstract

Growing concerns have been raised regarding the effects of disturbance due to agricultural practices on associate biodiversity and on the ecosystem services that biodiversity provides. Surprisingly little is known about the effects of such disturbances on complex agroecosystems with multiple interacting species. The aim of this study was to assess the effects of management by pesticide spraying on the productive outputs and the ecological functioning of a cacao agroecosystem. We built a mechanistic dynamic model including the dynamics of the crop, a pest (Cacao Pod Borer, Conopomorpha cramerella) and two beneficial insects: a hymenopteran egg-parasitoid and a ceratopogonid pollinator. Using this model, we tested the effects of a range of pesticide types characterized by their impacts on both the Cacao Pod Borer and the beneficial insects. Our results showed that yield strongly varies according to both pesticide type and timing of pesticide application. The type of pesticide had a strong influence on the flexibility of management. No simple spraying decision rule led to maximal yields for all types of pesticide. Although optimal spraying strategies differed with the type of pesticide used, they all showed a similar pattern, i.e. they limited and postponed the Cacao Pod Borer population peak while limiting the negative impacts on beneficial organisms. The results highlight the non-trivial effects of pesticide application in complex agroecosystems where associated biodiversity provides both ecosystem services and disservices. They illustrate the critical importance of providing good information to farmers on pesticide management because the use of pesticides can have a negative effect on production by decreasing ecosystem services such as pollination.