Modeling the consequences of agricultural intensification on pest damage

It is accepted in the scientific literature that agricultural intensification (i.e. large monocultures) results in increased damage by pests. This notion is mainly based upon the resource concentration hypothesis that predicts that specialized herbivores can more readily locate, persist and increase in density in monocultures. This prediction has been supported by many empirical studies. However, most of these studies were conducted in relatively small plots or on perennial vegetation. We suggest that the extrapolation of these results to large monocultures and from perennial to annual vegetation could be misleading. We used a simulation model to explore the relationship between monoculture crop size and accumulated pest densities. We explored the effects of natural enemy presence, migration distance, reproduction rate and the ability of the pest to overwinter in the field on this relationship. Our results suggest that when the pest overwinters in the field, there is a positive correlation between monoculture crop size and mean cumulative pest densities in the focal field. However, this is not necessarily the case when the pest and its enemy enter into the field from the surrounding matrix. For example, when the predator mobility is larger than the mobility of the pest, a negative correlation between pest damage and size of monocultures is obtained. Thus, our conclusions are that under certain realistic conditions, increasing the size of monocultures can help reduce pest damage and consequently the use of pesticides. This may be especially true in annual crops where pests do not overwinter.