The biostimulants and NPK fertilizer affect the physiological and biochemical responses of cucumber plants and the ecological fitness parameters of Aphis gossypii (Hemiptera: Aphididae).

Application of fertilizers can be a feasible strategy for enhancing plant defenses. This study was conducted to explore the impacts of biostimulants, including fulvic acid (FA) and Ascophyllum nodosum L. extract (AnE), along with NPK fertilizer and their combinations (FA + AnE, FA + NPK, AnE + NPK, and FA + AnE + NPK) on the physiological and biochemical traits of cucumber plants in uninfested and aphid (Aphis gossypii Glover)-infested conditions. Furthermore, the subsequent effects of these treatments on fitness parameters of A. gossypii were investigated. The results revealed that plants treated with FA + AnE + NPK treatment had the highest levels of enzymatic antioxidants and nonenzymatic antioxidants compared with the uninfested control plants. Following aphid infestation, total phenolic content and antioxidant enzyme activities significantly increased in all treatments. Photosynthetic pigment contents were higher in uninfested treated plants, while they significantly declined after aphid infestation. The scavenging activities of malondialdehyde, hydrogen peroxide, and DPPH (1,1-diphenyl-2-picrylhydrazyl) were differently affected under infested and uninfested conditions compared with the control. Biostimulant- and fertilizer-treated plants significantly affected the population of A. gossypii, with the lowest preadult survival, fecundity, r (intrinsic rate of increase), λ (finite rate of increase), and GRR (gross reproductive rate) recorded on FA + AnE + NPK-treated plants. Overall, the findings revealed that the studied treatments, particularly FA + AnE + NPK treatment can potentially be considered as a sustainable pest management strategy for increasing cucumber resistance to A. gossypii by altering plant traits and aphid fitness.