The mealybug, Phenacoccus solenopsis Tinsley, a polyphagous pest with a wide host range is of recent occurrence on Bt cotton in all the three major cotton growing zones in India. The first perceptible appearance of the pest on cotton in Warangal district of Andhra Pradesh was noticed in Kharif 2008. P. solenopsis was recorded on several plants other than cotton which include cultivated crops and weed hosts. The mealybug population is naturally regulated by Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae). This paper reports the dynamics of this key parasitoid in a spatio-temporal perspective. Monitoring of the parasitoid on P. solenopsis occurring on weed hosts found on field bunds, crop fallows, barren lands, roadsides and village backyards indicated its activity on eight weed hosts late in the cotton growing season of 2009. During the year 2010, its activity started early in the season on few weed hosts while many more supported parasitization late in the season. Parasitoid activity was higher (11.3 to 15.3%) initially on the key hosts (Corchorus olitorius L., Abutilon indicum L., and Sida acuta Burm. F.) early in the season (August) which later shifted gradually to the main host (cotton) during the later part of the season. Cropping system and spatial perspective indicated that cotton fields adjacent to roadside and crop fallows supported higher parasitization during September (8.3-9.1%) and cotton fields adjacent to barren lands in December (13.3%). These findings have implications for the management of P. solenopsis mealybug on cotton from an agro eco-system perspective.