Asymmetric assortative mating between two hybridizing Orchelimum katydids (Orthoptera : Tettigoniidae)

The katydids Orchelimum nigripes and O. pulchellum (Orthoptera: Tettigoniid ae) have a largely allopatric distribution in the eastern United States, bu t hybridization between these species has been well documented in two conta ct zones, I used animals from populations just outside a narrow, recently f or med upstream-downstream hybrid zone along the Potomac River near Washing ton, D.C., in laboratory mate-choice trials to examine the possible importa nce of differential patterns of mate preference in determining the structur e and dynamics of this hybrid zone. Offered a choice between a male of each species, O. nigripes females showed an extreme preference for conspecific mates, but O. pulchellum females showed no clear preference. This asymmetry in mate discrimination may contribute to the apparently ongoing replacemen t along the Potomac of O. pulchellum by O. nigripes in the wake of a moving hybrid zone.