Do diverse landscapes provide for effective natural pest control in subtropical rice?

1. While the biocontrol potential of natural enemies is well established, it is largely unknown how landscape-mediated effects on pest and natural enemy communities impact the cascade of biocontrol potential, crop injury, yield and profit, taking into account crop management and surrounding landscape composition.

2. We compared natural biocontrol with chemical control according to local farmers' practice, across the 'full cascade' from natural enemy and pest abundance to crop injury, yield loss, yield and economic performance. This 2-year study was conducted in 20 rice fields embedded in a gradient of landscapes from crop-dominated to semi-natural habitat-dominated, in subtropical China, the world's largest rice-producing region.

3. Natural enemies suppressed brown planthopper population growth in unsprayed plots, irrespective of landscape composition. However, crop injury was lower in pesticide treated plots than in unsprayed plots, and yields in sprayed plots were 20% higher than in unsprayed plots. Nevertheless, pesticide applications were only profitable in less than half of the cases when only costs for pesticides were considered, and in less than one third of the cases when costs for pesticides and labour were considered.

4. Synthesis and applications. Our findings question the cost-effectiveness of current chemical-based pest management in farming, and highlight opportunities for more ecologically based pest management strategies based on the widespread activity of natural enemies. Pest damage and biocontrol, however, are largely independent from the landscape context, which might be due to the small-scale character of Chinese rice landscapes. To maintain high levels of biocontrol, conserving this small-scale character appears more important than increasing the proportion of semi-natural habitat.