How agricultural techniques mediating bottom-up and top-down regulation foster crop protection against pests. A review

Abstract

The heavy use of synthetic pesticides in agriculture has been responsible for detrimental effects on human and environmental health, making it necessary to develop more sustainable pest management strategies. A promising approach consists in the integration within cropping systems of agricultural techniques producing bottom-up effects or supporting top-down regulation of crop pests. However, there is still a lack of information on the extent to which this approach is currently being developed. In this paper, we review the last 10 years of published literature on the use in annual cash crops of three agricultural techniques: (i) crop spatial diversification, (ii) crop temporal diversification, and (iii) soil management influencing crop pests either through bottom-up effects or by supporting the top-down regulation of four categories of bioprotection agents: (i) macro- and (ii) micro-organisms, (iii) semiochemicals, and (iv) natural substances. We found that each agricultural technique is adopted to support a specific bioprotection category and to control a specific pest taxon. Crop spatial diversification was generally found to target herbivorous insects and to support macro-organism bioprotection agents. Crop temporal diversification and soil management mainly targeted pathogenic fungi and supported microorganism bioprotection agents. Despite the widespread idea that semiochemicals and natural substances are promising agents for pest regulation, their adoption remains largely unexplored. We also found that agricultural techniques are mostly adopted to support bioprotection in a conservation biological control approach while ignoring augmented bioprotection. In addition, the top-down regulation by means of bioprotection supported by agricultural techniques is just as effective against crop pests as the bottom-up effect produced by the agricultural techniques alone. We argue that a concerted effort to integrate bioprotection with agricultural techniques would open new research opportunities to reduce synthetic pesticide inputs fostering the transition from a conventional agriculture towards sustainable agroecosystems.