Predator–prey interactions in rice ecosystems: effects of guild composition, trophic relationships, and land use changes — a model study exemplified for Philippine rice terraces

A model study is presented that investigates the effect of land use changes on arthropods in Philippine rice terraces. These changes include the increase of non-rice areas (vegetable fields and woodlots), the introduction of a second cropping season and the abandonment of the traditional synchrony in the cropping regimes over whole regions. Such changes are likely to have an effect on the balance between rice pests (plant and leaf hoppers, e.g. Nilaparvata lugens and Sogatella furcifera) and their natural enemies (spiders, predatory bugs and parasitoids), and therefore could be of considerable interest in the context of pest management. The model explicitly considers several arthropod species and their population dynamics in several rice fields with different cropping cycles. Thus various spatio-temporal land use regimes can be investigated and compared in their effect on pest abundance. According to the model results, a high proportion of vegetable fields reduces pest abundance. Whether synchronous cropping reduces pest abundance, depends on the interactions between their natural enemies, particular the feeding behaviour of the mirid bug Cyrtorhinus lividipennis. A cropping regime that minimises pest abundance in all circumstances, does not exist. Whether traditional farming practices are superior to modern ones or not, is very much influenced by the type of integration of different control strategies and tactics and the ecology of the species involved.