The simulation model (MiteSim) of the mite predator-prey system consisting of Banks grass mite,Oligonychus pratensis(Banks), and the predatory miteNeoseiulus fallacis(Garman) was used to evaluate mite population dynamics in Nebraska corn fields in relation to microenvironmental variables. Simulation results demonstrated the importance of using humidity and temperature conditions at the leaf surface instead of weather station conditions to simulate the mite system on corn in Nebraska. Also, humidity (in addition to temperature) was determined to be critically important in the population dynamics of the two mites. The temperature and humidity at the leaf surface of moderately drought-stressed corn (compared with well-watered corn) resulted in higher simulated populations of Banks grass mite. Simulation studies also showed that colonization of a corn field by less than one adult female Banks grass mite per plant in June can result in mite densities sufficient to cause crop loss by August (Banks grass mite biotic potential without extrinsic mortality).