Seasonal history of green citrus aphid Aphis spiraecola Patch was studied in terai belt of eastern Uttar Pradesh, India during three consecutive years, 2006, 2007 and 2008. The green citrus aphid appears during the first week of November on Cosmos bipinnatus and attains a peak during third week of December during 2006-2007. Cause of increase in the population during first half of the November in the field seems due to healthy plants, favourable temperature (around 25oC) and humidity (above 40% RH) and less predatorism/parasitism. Decrease in population after the peak population may be attributed to low humidity (less than 50% RH) and predatorism/parasitism along with maturity of the crop. Since its population attains single high peak during the crop season, its population can easily be regulated by using any eco-friendly management practice by enhancing the activities of predators (particularly ladybird beetles) as they come along with the aphid.