Heliothis armigera, the cotton bollworm, is an important cotton pest in Tanzania and also attacks some food crops grown in the cotton areas. A study was done in cropping systems practised by small scale farmers in Western Tanzania. The objective was to examine the bionomics of the pest in this agro-ecosystem with emphasis on improved integrated control strategies. The level and timing of HL armigera infestations were studied on maize, sorghum, cotton, chickpea, tomatoes and Cleome sp. The attractive stages of these crops provide overlapping hosts throughout the year. Chickpea and tomato production during the dry season in the study area has enabled the pest and its natural enemies to survive the dry season, this bridging an otherwise unfavourable period. Larval mortalities were assessed on its different hosts. Adequate rainfall favoured the build up of the pest whereas dry weather caused drastic population decline. Larval diseases and parasitism were important but neither prevented the pest population from causing economic damage to the cotton crop. Prospects for forecasting pest attack on cotton from infestations on other hosts, notably maize, showed that the greatest benefit is in predicting the timing of the early infestations.