Data from: Nitrogen fertilizer input alters the prey consumption rate of a widespread aphid predator, Harmonia axyridis

The sharp rise in synthetic inorganic fertilizer use (notably nitrogen) over decades has caused unknown effects on ecosystems and the services they provide, such as biocontrol. The present study aimed to test the hypothesis that host plant nitrogen input alters the interactions between pests and natural enemies, specifically investigating whether aphid consumption by Harmonia axyridis differed depending on nitrogen fertilizer input. It was hypothesised that H. axyridis would consume fewer aphid individuals reared under nitrogen conditions that are optimal for aphid fecundity. Observed effects of different nitrogen inputs in Chinese cabbage on the aphid Myzus persicae and the predator H. axyridis support our hypothesis: at lower nitrogen levels, the fecundity and longevity of M. persicae increased in the absence of predators, and the numbers of adult aphids H. axyridis consumed to reach temporary satiation and to finish the 3rd and 4th instars decreased. In addition, the fitness of H. axyridis, indicated by the pupal weight, also reduced at the nitrogen treatment favourable for aphid fecundity. These findings revealed the mechanisms underlying the long observed amplified changes in biocontrol efficacy with different nitrogen inputs in agroecosystems that reducing nitrogen for plants increases pest fecundity while reduces predation. Therefore, we recommend an economical increase in nitrogen application to achieve optimal plant nutrition and enhance biocontrol efficacy of the ladybeetles.