Semi-natural habitat of gullies mediates the spatiotemporal pattern of beneficial insects in an agricultural watershed in Northeast China

Abstract

Gullies with the semi-natural habitat (SNH) are widely distributed in the arable land of the watershed. However, the ecological functions of these gullies, especially for the dynamics and distribution of beneficial insects (BI) are still not clear. In this study, the spatiotemporal dynamic of BI influenced by herbicides application, plant diversity, soil moisture (SM) and climatic factors was investigated in thirteen gullies and adjacent farmlands from a watershed during the crop growth stages. The main results showed that both the abundance and richness of BI were highest in the gullies and adjacent areas compared with the forest belt, grassland and farmland in the watershed. The gathering phenomenon was strengthened after herbicide application and crop harvest. The abundance and richness of BI were relatively higher in farmland during stages of no herbicide application and no crop harvest compared to after herbicide application and harvest. The abundance and richness of BI were typically highest in the gully middle than the head and tail of both stable and developing gullies in most seasons. However, after herbicide application, the abundance and richness of BI were highest in the gully head in stable gullies and the mean values were 3.1 and 3.6 times that of farmland, while in developing gullies were still highest in the gully middle and the mean values were 2.8 and 3.5 times that of farmland. BI dynamics were mainly determined by the abundance and richness of plants in gullies, while SM less influenced the BI. Interspecific associations of BI were significantly positive in the watershed but were not significantly positive in the single gullies. Generally, gullies are the most important source and sink of BI compared with the forest belt and grassland, which can significantly mediate the spatiotemporal pattern of BI in the agricultural watershed.