Predators do not benefit from crop diversity but respond to configurational heterogeneity in wheat and cotton fields

Context Manipulating crop diversity in the landscape has been suggested as a promising management option to enhance biocontrol but how crop diversity independently of other important aspects of landscape structure affects predator and pest abundances remain largely unexplored.Objectives Our study assessed the relative and interactive effects of crop composition and configuration on aphids and their generalist predators, i.e. ladybirds, spiders and lacewings.Methods We sampled arthropods in 47 cotton fields and 21 wheat fields in Hebei, China, located along three landscape gradients: crop diversity (Shannon diversity of crops ranging from 0.27 to 1.32 corresponding to a crop richness varying from 2 to 7 different crops), crop configurational (crop edge density varying from 0.0012 m/ha to 0.066 m/ha) and proportion of semi-natural habitats (varying from 0.5% to 56%).Results Crop diversity never had any effect on arthropod communities and we found no effect of the proportion of semi-natural habitats on natural enemies' abundances. Aphid abundance was positively correlated with the proportion of semi-natural habitats both in cotton and wheat fields. Lacewing abundance benefited from configurational heterogeneity as abundances increased with crop edge density.Conclusions Our result provide evidence that crop diversity is probably not the best management option to enhance biocontrol of aphids in Chinese landscapes and confirms that the amount of semi-natural habitats in the landscape is a critical aspect shaping arthropod communities. It also indicates that manipulating crop edge density by promoting agricultural landscapes with small field size for instance can benefit natural enemies of crop pests.