Cascade effects of crop species richness on the diversity of pest insects and their natural enemies.

Peijian Shi,Haifeng Cao,Zihua Zhao,Xingyuan Men,Cang Hui,Feng Ge,B Larry Li,Xianshi Jin,Fang Ouyang

doi:10.1007/s11427-014-4681-7

Abstract

Understanding how plant species richness influences the diversity of herbivorous and predatory/parasitic arthropods is central to community ecology. We explore the effects of crop species richness on the diversity of pest insects and their natural enemies. Using data from a four-year experiment with five levels of crop species richness, we found that crop species richness significantly affected the pest species richness, but there were no significant effects on richness of the pests' natural enemies. In contrast, the species richness of pest insects significantly affected their natural enemies. These findings suggest a cascade effect where trophic interactions are strong between adjacent trophic levels, while the interactions between connected but nonadjacent trophic levels are weakened by the intermediate trophic level. High crop species richness resulted in a more stable arthropod community compared with communities in monoculture crops. Our results highlight the complicated cross-trophic interactions and the crucial role of crop diversity in the food webs of agro-ecosystems.

Highlights

Understanding how plant species richness influences the diversity of herbivorous and predatory/parasitic arthropods is central to community ecology
If the resource concentration hypothesis (RCH) holds, the species richness or density of pest insects would be affected by crop species richness, with natural enemy communities affected by the species richness of pest insects
We found no significant differences in pest insect abundance among the five levels of crop species richness (Figure 1; F1881=1.007, P=0.316) and natural enemy abundance showed no significant differences among different crop species richness (F1881=0.640, P=0.424)

Summary

Introduction

Understanding how plant species richness influences the diversity of herbivorous and predatory/parasitic arthropods is central to community ecology. Using data from a four-year experiment with five levels of crop species richness, we found that crop species richness significantly affected the pest species richness, but there were no significant effects on richness of the pests’ natural enemies. Few studies have examined the food webs at three trophic levels, such as crops, herbivore pests and their natural enemies in certain agro-ecosystems [12 14]. Agro-ecosystems are closely associated with crop production, with more research required to elucidate all possible interactions in the tri-trophic system of crops, pest insects, and their natural enemies. If the NEH holds, polycultures should increase the species richness of natural enemies in agro-ecosystems, reducing the population and species richness of pest insects. Our study elucidates all three interactions in this tri-trophic agro-ecosystem, allowing us to test the RCH and the NEH using field experiments

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