Native Japanese Polygonaceae Species as Potential Native Insectary Plants in Conserving Indigenous Natural Enemies

Conservation biological control (CBC) is the application of agricultural practices that utilize insectary plants to conserve and enhance natural enemies, thereby increasing their efficiency to suppress pests. Most of the insectary plants used in CBC are non-native invasive insectary plants, which are costly and pose threats to the local ecosystems and biodiversity. Alternative to non-native insectary plants, the use of native plants is proposed. Hence, the aim of this study is to identify native plant species that can be used as alternatives to non-native insectary plants to conserve and promote indigenous natural enemies (INEs) for sustainable pest management. To achieve this, first, we bio-prospected the surrounding habitats of organic fields in the western region of Japan (i.e., Hiroshima Prefecture) to identify native plant species as prospective native insectary plants. As a result, among various Japanese native plants surveyed, Polygonaceae plant species seem to host a variety of INEs, showing potential as a native insectary plant. We then conducted open field experiments to test the role of Polygonaceae plants in promoting INEs, thereby indirectly suppressing pest densities on vegetable crops such as eggplants. Results show that significantly high densities of INEs (green lacewing, p = 0.024; Orius spp., p = 0.001: GLM) were observed on eggplants with Polygonaceae plants compared to eggplants without Polygonaceae plants, leading to a significant reduction in pest densities (thrips, p = 0.000; whiteflies, p = 0.002: GLM) on the eggplants with Polygonaceae plants. Furthermore, molecular analysis revealed that Orius spp., as a representative INE in this study, migrated from Polygonaceae plants to eggplants, suggesting that Polygonaceae plants may conserve and promote INEs to vegetable crops, resulting in pest suppression. Here, we discuss the roles of Polygonaceae plants (and other native plants) in regulating pest densities on crops.