Lysiphlebus testaceipes (Cresson) mummies and adults were cooled for various periods of time to determine their functional cold hardiness and survival at temperatures commonly experienced in the Southern Great Plains. Subsequently, surviving parasitoids were exposed to several greenbug, Schizaphis graminum (Rondani) hosts, to determine whether the temperature extreme they survived adversely affected oviposition.  Lysiphlebus testaceipes females survived regimens that cooled the parasitoid to 2, -2, and -6° C for 12 h, however at -8° C, all L. testaceipes specimens perished.  Female parasitoids that survived cooling treatments were able to oviposit when warmed to 22° C. Some L. testaceipes adults were able to survive up to 21 d at 5° C and oviposit successfully when warmed to 22° C.  Lysiphlebus testaceipes mummies were observed to survive up to 28 d at -5° C and oviposit successfully when warmed to 22° C.  These cold temperature survival abilities along with observations that parasitoids are actively foraging at temperatures well below 14°C in the field provide insights about how L. testaceipes, when it is present in sufficient numbers, is able to effectively prevent greenbug populations from increasing in winter wheat agro-ecosystems.