none The armyworm, M. separata (Walker) has been gaining importance as a pest of wheat in the Punjab since the introduction of Mexican varieties in early sixties. It has been observed to appear sporadically during certain years. There was an unprecedented outbreak of this pest during April 1980 in some villages of Ludhiana, Jullundur and Ferozepur districts. Field observations on the larval population, extent of parasitism and disease incidence were recorded in eight villages at the time of peak population of this pest. A very high larval parasitism (up to 95%) by a braconid (Apanteles ruficrus ) and quite high viral disease incidence acted as important mortality agents and contributed to sudden decline of the population before entry into pupal stage and carry over to the next season. Observations in the same localities during 1981 showed that the population of armyworm remained much lower except in two fields. The extent of parasite and disease incidence were also low. The results are discussed in relation to build up, dispersion and decline of the population as affected by various mortality agents.