Parasitism of parasitoid Aphidius colemani Viereck in Rhopalosiphum padi and its control efficacy against green peach and cotton aphids were studied in greenhouse. The number of mummies was the highest in 1-day old nymphs and the lowest in 7-day old aphids. The mummy produced by 1 female was 105.5 and 71 individuals at 25 and $20^{circ}$, respectively. No mummy was observed at 15 and $30^{circ}$. So, condition for parasitism of A. colemani involved about $25^{circ}$ to $20^{circ}$ as a temperature and young aphid instar. Application of banker plant for release and maintenance of the parasitoid resulted in effective and economic control of green peach and cotton aphids in watermelon-, red pepper-, and cucumber-greenhouse.