Increasing the proportion of flower strip area in farmland promotes natural enemies to enhance aphid biocontrol and wheat yield

Sowing flower strips adjacent to crops is an effective practice for promoting natural enemies, enhancing biological pest control services and conserving biodiversity. However, few studies have considered the relationships between the proportion of within-field flower strips and the abundance of pests and natural enemies, pest control and wheat yield. A three-year field experiment was conducted in wheat plots using a randomized block design, with four proportions (i.e. land area covered by flower strips within the total plot area) of flower strips sown with Cnidium monnieri, which were 0% (without flower strips), 5% (one flower strip on west margin of plot), 10% (two flower strips on east and west margins), and 15% (flower strips on east margin, west margin and the centre of the plot). We monitored the abundance of aphids, predatory insects and mummified aphids, and quantitatively evaluated both pest control services and wheat yield. The predator abundance, pest parasitism rates, relative biocontrol service index (RBSI) and wheat yield were significantly higher in the treatments (5%, 10% and 15%) than those in the 0% treatment. Importantly, the aphids abundance in the treatments (5%, 10% and 15%) decreased by 27%, 35% and 37%, respectively, compared with that in the 0% treatment. With an increasing proportion of flower strips, the predator abundance, parasitism rate, and yield increased, whereas the aphid abundance decreased. In conclusion, sowing 10% or 15% strips of C. monnieri flowers within-filed is a promising measure for providing considerable biocontrol services and sustaining wheat yields.