Abstract
Many studies have supported the enemies hypothesis, which suggests that natural enemies are more efficient at controlling arthropod pests in polyculture than in monoculture agro-ecosystems. However, we do not yet have evidence as to whether this hypothesis holds true in peach orchards over several geographic locations. In the two different geographic areas in eastern China (Xinchang a town in the Shanghai municipality, and Hudai, a town in Jiangsu Province) during a continuous three-year (2010–2012) investigation, we sampled arthropod pests and predators in Trifolium repens L. and in tree canopies of peach orchards with and without the ground cover plant T. repens. No significant differences were found in the abundances of the main groups of arthropod pests and predators in T. repens between Hudai and Xinchang. The abundance, richness, Simpson's index, Shannon-Wiener index, and Pielou evenness index of canopy predators in ground cover areas increased by 85.5, 27.5, 3.5, 16.7, and 7.9% in Xinchang, and by 87.0, 27.6, 3.5, 17.0 and 8.0% in Hudai compared to those in the controls, respectively. The average abundance of Lepidoptera, Coleoptera, Homoptera, true bugs and Acarina canopy pests in ground cover areas decreased by 9.2, 10.2, 17.2, 19.5 and 14.1% in Xinchang, and decreased by 9.5, 8.2, 16.8, 20.1 and 16.6% in Hudai compared to that in control areas, respectively. Our study also found a higher density of arthropod species resources in T. repens, as some omnivorous pests and predators residing in T. repens could move between the ground cover and the orchard canopy. In conclusion, ground cover in peach orchards supported the enemies hypothesis, as indicated by the fact that ground cover T. repens promoted the abundance and diversity of predators and reduced the number of arthropod pests in tree canopies in both geographical areas.
Highlights
The enemies hypothesis argues that natural enemies are more effective at controlling arthropod pests in diverse ecosystems than in simple ones [1,2,3]
In our former study in Shanghai municipality and Jiangsu province in eastern China, we observed that the arthropod pests in T. repens mainly included Homoptera, Lepidoptera, true bugs, Acarina and Coleoptera, while the predators in T. repens mainly included Araneida, Coleoptera, Neuroptera, Diptera and Hemiptera. We found that these species provided an excellent pool for canopy arthropods in peach orchards [19]
The factors of site and year had no significant effects on the abundance of arthropod pests of Lepidoptera, Homoptera, true bugs, Acarina or Coleoptera, and the same effects were indicated by the interactions of the two factors (Table 1)
Summary
The enemies hypothesis argues that natural enemies are more effective at controlling arthropod pests in diverse ecosystems than in simple ones [1,2,3]. As an important diversified plantation model [9,10,11], has played a key role in enhancing crop yield, productivity, and stability in ecosystems [12,13,14]. Shanghai municipality and Jiangsu province in eastern China are the two most important peachgrowing regions: both Shanghai, with an annual peach cultivation area of 1.56104 ha and peach yield of 1.86108 kg, and Jiangsu, with an annual peach cultivation area of 3.26104 ha and a peach yield of 3.56108 kg, have acquired national recognition as peach growing areas
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