Pest management is an intensive decision making system requiring efficient decision tools. Mainly two types of decisions are relevant in pest management: tactical and strategic. These decisions need information on crop losses due to pests for control intervention and research prioritization, respectively. Traditionally the crop losses have been determined through empirical yield-infestation relations, which by nature are site specific and can not be extrapolated without risk of error. These are thus needed to be established for each location independently which is a difficult proposition. Chander and Singh (2001) established empirical yield infestation relations for leaf folder, Cnaphalocrosis medinalis incidence on Pusa 169 rice as y = 91.82 – 1.04 x (R2 = 0.58) in one year and as y = 100.19 – 0.504 x (R2 = 0.88) in another year. The relations were thus quite different and Economic Injury Level (EIL) determined with these was found to be 4 and 8 % during two years, respectively. Mechanistic approach i.e. continuous dynamic crop growth simulation models can help to overcome this lacuna of the empirical models. These models are based on crop physiological and ecological processes and can account for diversity in soil, genotype, management, weather and pest situations, which are inherent in the environment and can thus be used for deriving site specific decision support tools promptly. Use of simulation models in plant protection began in 1960s but in beginning only pest dynamics was simulated without its linkage with crop growth. Subsequently crop growth simulation models were coupled with pest damage mechanisms and pest losses were simulated but this was termed as one way approach of simulating crop-pest interactions as effect of pest population on crop growth and yield could be simulated but reverse could not be achieved. However coupling of pest population models with crop growth models realized two way simulation of crop-pest interaction where pest and crops influenced each other in a dynamic mode. Crop-pest models have been used for various applications in the field of pest management such as formulation of decision support tools like EILs and iso loss curves for rationalizing pesticide use, pest risk analysis, pest zonation, pest forecasting, determining potential yield, yield gap analysis, GxE interactions, estimating efficacy and longevity of host plant resistance, assessing impact of global climate change on agricultural productivity, and evaluating impact of transgenics on environment. Chander et al. (2005) and Satish (2004) simulated EILs for Russian wheat aphid and rice leaf folder respectively. The simulated EILs compared well with empirically driven EILs, thereby demonstrating utility of simulation models for devising site specific decision tools. Daryaei (2003) formulated iso loss curves for stem borer and BLB in rice and leaf rust and stem borer in wheat which could be used for pest monitoring and judicious application of pesticide application. Mostly simulation models have been used for point application but with availability of regional databases on crop management, pest density and other variables, these can be used for regional applications. With increasing cultivation of transgenic crops and with greater concern regarding impact of global climate change on pests and crop productivity, the crop growth simulation models would play bigger role in future. References: Chander, S., Ahuja, L.R., Peairs, F.B., Aggarwal, P.K. and Kalra, N. 2005. Modeling the effect of Russian wheat aphid, Diuraphis noxia (Mordvilko) and weeds in winter wheat as guide to management. Agricultural Systems (accepted). Chander, S. and Singh, V. S. 2001. Distribution, economic injury level and sequential sampling of leaf folder (Cnaphalocrosis medinalis) on rice (Oryza sativa). Indian Journal of Agricultural Sciences 71 (12): 768-71. Daryaei, M.G., Aggarwal, P.K., Chander, S. and Singh, V.S. 2003. Use of simulation model to formulate iso-loss curves for stem borer and bacterial leaf blight incidence in rice. Indian J. Ent. 65(4): 532-543. Satish, D.G. 2004. Quantification of damage mechanism and determination of economic injury level for leaf folder, Cnaphalocrosis medinalis in rice. Ph.D. thesis, P.G. School, Indian Agricultural Research Institite, New Delhi, India.