Landscape-scale habitat diversity and agricultural pest management: a meta-analysis

Increasing diversity in agricultural systems at the local scale, by intercropping, is known to generally suppress specialist herbivore densities and to increase natural enemy densities. However, despite their pest-suppressing properties, polycultures have not been widely adopted in industrial agricultural systems for a variety of agronomic and economic reasons. Diversity can also be added to agricultural systems at the landscape-scale, by increasing the number of crops, the amount of pasture, and/or the amount of non-crop habitat in a region. Nearly 50 studies have been conducted that examine the effects of landscape-scale diversity on insects in agriculture. We report a meta-analysis on the existing literature examining the relationships between landscape-scale habitat diversity and 1) natural enemy densities, 2) natural enemy diversity, and 3) herbivore densities. Data indicate that the densities and diversity of natural enemies are higher and that herbivore densities are lower in diverse agricultural landscapes. Exceptions appear related to habitat specialization. This research supports arguments that agricultural diversity promotes ecosystems services, specifically biological control and natural pest suppression.