Biological and Physiological Changes in Spodoptera frugiperda Larvae Induced by Non-Consumptive Effects of the Predator Harmonia axyridis

The effects of predatory natural enemies on their prey or hosts involve both consumption and non-consumptive effects. This study investigated the non-consumptive effects of the predator, Harmonia axyridis (Coleoptera: Coccinellidae) on 1st, 2nd and 3rd instar larvae of Spodoptera frugiperda. We exposed larvae of different instars to the predator and assessed various parameters using a combination of biological and biochemical methods. Exposure to the predator significantly affected the growth and development of the S. frugiperda caterpillars. Firstly, the developmental duration of S. frugiperda larvae in the 1st–3rd instars and the pupal stage were notably prolonged. Moreover, we observed significant effects on pupal mass, pupal abnormality rate and emergence rate. These non-consumptive effects were gradually weakened with an increase in the larval stage exposed to the predator. Antioxidant enzyme activities including catalase (CAT) peroxidase (POD) and superoxide dismutase (SOD) activity increased significantly. Additionally, organismal triglyceride, trehalose and glycogen content were significantly altered by non-consumptive effects, while protein content showed no significant change. Spodoptera frugiperda larvae increased the activity of antioxidant enzymes in response to potential predators to mitigate oxidative stress and reduce cellular and tissue damage. This resources redistribution towards survival may inhibit growth and development of the species and further exacerbate these non-consumptive effects. These findings highlight the importance of considering non-consumptive effects in pest-management strategies to optimize control measures in agricultural systems.