Intercropping flowering plants facilitate conservation, movement and biocontrol performance of predators in insecticide-free apple orchard

Habitat management is an important approach suppressing pest via conservation biological control in agricultural systems. Intercropping flowering plants is a well- practiced habitat management measure, supporting predators with shelter, nectar, alternative prey and pollen. However, few studies systematically revealed predator’s conservation performance, transfer process and biocontrol ability by intercropping flowering plants in apple orchards. Here, an experimental model of intercropping flowering plants in apple orchard was planned for two consecutive years to response above questions. Four flowering plants conserve a different number and proportions of six main predator species (three ladybeetles (Propylaea japonica, Harmonia axyridis and Hippodamia variegata), one lacewing (Chrysoperla sinica), one hoverfly (Episyrphus balteatus) and one spider (Misumenops tricuspidatus)). By rubidium (Rb) marking technique, transfer rate of predators C. sinica from flowering plant Cnidium monnieri to apple trees were 79.5 % and 84.1 % in 2020 and 2021, respectively. Transfer rate of predators H. axyridis from flowering plant C. monnieri to apple trees were 74.2 % and 80.1 % in 2020 and 2021, respectively. By predator exclusion trials, the Biocontrol Services Index (BSI) was calculated in sampling date, in which the number of aphids on the caged and uncaged branch has significant difference in the four flowering plants and untreated control plots in 2020 and 2021, respectively. Thus, our results suggest that, intercropping flowering plants in insecticide-free apple orchard contributed to increase the number of predators and biological control of aphid Aphis spiraecola. These findings support that intercropping flowering plants as a promising management option could be implemented in apple orchards.