Characterization of core maize volatiles induced by Spodoptera frugiperda that alter the mating-mediated approach–avoidance behaviors of Mythimna separata

The fall armyworm (Spodoptera frugiperda) is an invasive species and a destructive pest of maize, which significantly impacts native species and communities via complex mechanisms like competition for resources. However, the interaction between S. frugiperda and local pests remains unclear. In this study, we determined that Oriental armyworm (Mythimna separata) females with different mating status displayed different approach–avoidance behaviors towards maize which was infested by S. frugiperda larvae. The virgin M. separata females were repelled, while the mated females were attracted by the S. frugiperda-infested maize. To further understand the olfactory mechanism of this phenomenon, seven volatiles induced by S. frugiperda in maize were characterized by gas chromatography and mass spectrometry (GC-MS), including trans-2-hexenal, linalool, trans-β-farnesene, cis-3-hexenyl acetate, β-caryophyllene, trans-α-bergamotene, and isopentyl acetate. Additionally, electrophysiological and behavioral assays of the seven compounds were performed using both virgin and mated females of M. separata. We determined that virgin and mated females displayed different responses to the herbivore-induced plant volatile (HIPV). Trans-β-farnesene was the core compound for repelling virgin females, and trans-2-hexenal was the key attractant for oviposition in mated female M. separata individuals. These findings help our comprehension of the relationships between maize pests and offer new possibilities for controlling them by olfactory-based strategies.