In the recent years, nematic liquid crystals have attracted a great deal of interest owing to the high optical nonlinearity available by the molecular reorientation. Furthermore, this nonlinearity is known to be inherently highly non local owing to a strong intermolecular cohesion. For this reason, these materials have been the subject of several recent studies of fundamental interest such as the study of higher-order solitons and spontaneous modulation instability. In the present work, we investigate experimentally the behavior of a periodically modulated elliptical beam in nematic liquid crystals. We show that the optical nonlinearity leads to the amplification of the spectral sidebands corresponding to the initial modulation, a phenomenon known as induced spatial modulation instability.