Treatment of cotton with plant growth‐promoting rhizobacteria consortium alters host location and oviposition of Spodoptera exigua

BACKGROUND: Plant growth-promoting rhizobacteria (PGPR) trigger induced systemic resistance (ISR) in plants, which could impair herbivore's host location, oviposition behavior and development. A PGPR consortium (i.e., blend of strains) is often more effective than single strains, but its efficacy depends on crop cultivar, herbivore-crop system, herbivore's degree of specialization, etc. In this study, the efficacy of five PGPR consortia, hereafter named TX1, TX2a, TX3, AU8 and AU9a, was evaluated to screen the most promising consortia in controlling the polyphagous insect pest, Spodoptera exigua in two cotton cultivars (one susceptible and one resistant to pests). The effects of the PGPR treatments on oviposition behavior, larval development and olfactory responses of S. exigua, and on cotton volatile emissions were evaluated. RESULTS: Spodoptera exigua laid significantly fewer eggs on susceptible plants treated with AU8, AU9a, TX1 or TX2a, and on resistant plants treated with AU8, TX1 or TX3, compared to untreated plants. However, the difference in larval survival rates (81-83% in untreated plants versus 66-71% in PGPR-treated plants) was not significant. Y-tube olfactometer bioassays using the promising PGPR treatments revealed that headspace volatiles of susceptible plants treated with AU8 or TX1, and resistant plants treated with AU8, TX1 or TX3 were avoided by S. exigua when compared against blank air, indicating an inhibitory effect on S. exigua behavior. Gas chromatography-mass spectrometer analysis of headspace volatiles revealed that the most discriminant compounds between PGPR-treated and untreated plants were α-pinene, β-pinene, benzaldehyde, D-limonene, (Z)-3-hexenyl acetate, β-ocimene and DMNT. These compounds are known to modulate herbivore's host location and oviposition behavior. CONCLUSION: This study identifies two promising PGPR consortia (AU8 and TX1) and potential repellent compounds for the protection of cotton cultivars against S. exigua and discusses their role as part of an integrated pest management (IPM) approach. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.