Asymmetric Pheromone Interference and Intrageneric Antagonism Between the Invasive Spodoptera frugiperda and Sympatric Noctuid and Crambid Moths

The invasive fall armyworm, Spodoptera frugiperda, co-occurs with native moths in maize agroecosystems, yet their interspecific sex pheromone interactions remain poorly understood. We evaluated electroantennogram (EAG) and field behavioural responses among S. frugiperda, two native noctuids (S. litura, S. exigua), and two crambids (Conogethes punctiferalis, Ostrinia furnacalis). EAG analyses revealed widespread peripheral cross-recognition, with both sexes of S. frugiperda and all four sympatric moth species (including both male crambids) demonstrating significant electrophysiological responses to heterospecific pheromones, often at thresholds as low as 1 μg. In field trials, crambid lures had neutral effects on S. frugiperda captures, but S. exigua and S. litura pheromones inhibited its attraction. Reciprocally, the S. frugiperda pheromone reduced catches of all four sympatric species. These results reveal intrageneric reciprocal antagonism within Spodoptera alongside asymmetric interference with crambids. The neutrality of crambid pheromones toward S. frugiperda supports co-deploying crambid and S. frugiperda lures without compromising capture of the invasive pest; however, reciprocal suppression of crambid catches precludes multi-species monitoring in a single trap. Strict spatial segregation is required among Spodoptera traps to avoid false-negative data. If mediated by olfactory masking, the asymmetric suppression of crambids suggests that high-volume dispensers for S. frugiperda could also disrupt sexual communication of sympatric crambid residents.