Observations have shown that in some cases equatorial spread F (ESF) irregularities including plasma bubbles are related to temporal and spatial structures of electric fields. It has been conjectured that the electric field structures may be responsible to production of ESF bubbles. We present here numerical results of electric field effects in nonlinear evolution of ESF. In our simulations we have modeled electric field structures in both time and space. It is found that the temporal structures, including the prereversal enhancement, of the eastward electric field cause motion of the F layer in the vertical direction, but they cannot produce spatial structures of F region plasma. In contrast, plasma bubbles are produced when spatial structures of electric field are used as input in the simulations. The spatially irregular electric fields initiate plasma perturbations in the bottomside F region, then the perturbations are amplified by the Rayleigh-Taylor instability and evolve into topside plasma bubbles. It is concluded that spatial structures of electric field are needed for seeding of ESF bubbles. It is shown also that electric fields generated by E region gravity waves can result in production of F region bubbles. ¿ American Geophysical Union 1996