Repellent and attractive effects of herbs on insects in pear orchards intercropped with aromatic plants

There is increasing interest in the use of vegetation such as aromatic plants as intercrops to biologically control insect pests in agroecosystems and orchard ecosystems. Understanding the mechanisms underlying the repellent effects of aromatic plants on orchard pests (e.g., scarabaeid pests) can lead to improved application of intercropping cultivation practices in orchards. We tested eight intercropping treatments, each containing a different species of aromatic plant, in a pear orchard, along with a natural grass treatment and a clean tillage (control) treatment. The results showed that intercropping reduced the annual cumulative number and abundance of scarab beetles relative to the control. The annual dynamics of scarab populations were also significantly altered where intercrops were used. However, with the exception of Ichneunmonidae, the natural parasites of scarabs showed no preference for the aromatic plants. A correlation analysis indicated that the reduction in some of the scarab beetle species was related to the abundance of certain specific natural enemy species. In addition, the diversity, evenness and degree of dominance of natural enemy species may have contributed to the decrease in scarab populations. This study shows that intercropped aromatic plants can be applied to control the scarab beetles in orchard ecosystems, but that effects vary across aromatic plant species.