Objective This study aims to investigate the effects of non-consumptive effects (NCEs) of Harmonia axyridis (Pallas) on the growth, development, and reproduction of pea aphids, Acyrthosiphon pisum (Harris), over three consecutive generations. The results are expected to provide a theoretical basis for utilizing natural enemy NCEs in aphid control.

Method Three levels of predation stress by H. axyridis were established on broad bean plants: one ladybird with 30 aphids (30A+1P), two ladybirds with 60 aphids (60A+2P), and six ladybirds with 180 aphids (180A+6P) per plant. Control plants were infested only with aphids (0, 30, 60, and 180 aphids per plant, respectively). The developmental duration, body weight gain, and number of offspring produced were measured over three consecutive generations.

Result Under NCEs treatments: in the 30A+1P treatment, the developmental duration of the second-generation (G2) aphids is significantly shortened by 0.67 days. In the 60A+2P treatment, the developmental durations of both G2 and third generation (G3) aphids are significantly prolonged by 0.67 and 0.57 days, respectively, and G2 body weight gain is significantly reduced by 0.4 mg. In the 180A+6P treatment, G2 fecundity increases significantly by 12.3 aphids. Additionally, first generation (G1) body weight gain increases only with rising aphid number per plant. In G2, body weight gain is negatively correlated with both aphid number per plant and the predation stress intensity of H. axyridis. In G3, the overall predation stress intensity of H. axyridis shifts to a positive effect on body weight gain. Developmental duration is shortened only in G1 as the predation stress intensity of H. axyridis increases. Fecundity decreases across all generations with increasing aphid number per plant or predation stress intensity of H. axyridis, though the decline is less pronounced in treatment groups than in aphid-only controls. Intergenerational comparisons show that under NCEs, the pattern of aphid body weight gain shifts from G1 < G2, G3 in controls to G1 < G2; developmental duration changes from G1 > G2 > G3 to only G1 > G3; and fecundity shifts from G1 < G2 to G1 < G2, G3.

Conclusion The NCEs of H. axyridis reduce the population fitness of A. pisum by impairing aphid growth and development. However, after multigenerational exposure, aphids develop adaptive responses and may compensate for predation stress through increased fecundity.