Field experiments were conducted at the Institute for Agricultural Research (I. A. R.), Samaru, Zaria (Latitude 11Ëš11' N and Longitude 7Ëš38' E), Nigeria for two years period (2009 and 2012) to study the population dynamics of Agonoscelis versicolor F. on sunflower. The effect of planting dates of sunflower at two weeks intervals and weather parameters were used to monitor the population build-up of A. versicolor, their damage and yield of sunflower. The experiments were laid out in randomized complete block design with three replications. Four planting dates each during the rainy season (July 21, August 04, August 18 and September 01) and dry season (October 27, November 10, November 24 and December 08) were employed and Sunflower „Ex-Funtua‟ variety was sown with no insecticidal treatments. The result showed a significant difference (p <0.05) in the mean bug population on the sunflower on the four different planting dates, with higher mean number of A. versicolor recorded during the dry season than the rainy season. Planting dates also had significant effect on percentage seed damage (19-30%) and seed yield. Relative humidity, rainfall and yield were negatively correlated to population of A. versicolor while temperature and sunshine were positively correlated to the population of A. versicolor.