Effect of Plant Cultivar and Substrate on Plant‐Pest‐Predator Tritrophic Interactions and Biological Control Potential

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is one of the most destructive pests of greenhouse cucumber, and its sustainable management remains a major challenge. Enhancing biological control through plant‐mediated bottom‐up effects on herbivores and top‐down effects on their natural enemies offers a promising strategy for sustainable pest management. In this study, the effects of three cucumber cultivars (Vihan, Shahab, and Saba) grown in two cultivation substrates (soil and hydroponic) were investigated on the life table parameters of A. gossypii and its predator, Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae). Plant secondary metabolites (flavonoids and phenols) and antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO), were also evaluated to better understand plant‐mediated defense responses. The developmental time of A. gossypii ranged from 4.47 ± 0.30 days on Saba grown in soil substrate to 6.86 ± 0.29 days on Vihan grown in hydroponic substrate. Aphid fecundity ranged from 30.81 ± 0.94 offspring on hydroponically grown Vihan to 71.55 ± 2.00 offspring on soil‐grown Saba. The intrinsic rate of increase ( r ) ranged from 0.2796 ± 0.0022 to 0.3930 ± 0.0011 day −1 , with the lowest values recorded on Shahab and Vihan grown in hydroponic substrate and the highest on Saba grown in soil substrate. Chrysoperla carnea developed faster and exhibited a higher intrinsic rate of increase ( r = 0.1802 ± 0.0030 day −1 ) when fed on aphids reared on hydroponically grown Vihan than on aphids reared on other treatments. Furthermore, flavonoid and phenol contents, together with the activities of SOD, POD, and PPO, increased in plants grown in hydroponic substrate, particularly following aphid infestation. Regardless of cucumber cultivar, trichome density was consistently higher in plants grown in hydroponic substrate. Overall, our results showed that the Vihan cultivar grown in hydroponic substrate was the least suitable host for A. gossypii and, when combined with C. carnea , appears to offer the greatest potential for sustainable management of A. gossypii through complementary bottom‐up (plant–aphid) and top‐down (predator–aphid) interactions.