Intercropping and flower strips to enhance natural enemies and control aphids: a comparative study in cabbage fields of Japan and Germany

Diversifying crop habitats and controlling arthropod pests by cultivating “secondary plants” alongside a primary crop is a frequently discussed strategy. The effectiveness of using secondary plants to manage pests varies across countries, and is influenced by factors such as the target pest, plant species, experimental design, and climatic conditions. Consequently, we conducted a study investing the impact of intercropping wheat or barley with additional flower strips on controlling aphid pests in white cabbage fields in Japan and Germany.Query Our results in Japan supported the natural enemies hypothesis, leading to a significant reduction in populations of two pest aphids: the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), and the cabbage aphid, Brevicoryne brassicae (L.) (Hemiptera: Aphididae). Furthermore, intercropping and/or flower strips increased the proportions of natural enemies, including hoverfly larvae (Diptera: Syrphidae), ladybirds (Coccinellidae: Coleoptera), and parasitoid wasps (Hymenoptera: Braconidae), relative to the aphids. Hoverfly larvae, due to their high abundance, appeared to be Japan’s most effective aphid suppressors. In contrast, in Germany, intercropping and flower strips did not remarkably suppress aphid populations or enhance the presence of the natural enemies, despite a temporary increase in the population density of hoverfly larvae in intercropping. These disparities between the trials in the two countries may be attributed to variations in regional and local biodiversity. This suggests that using secondary plants for pest control should consider the specificities of local environments.