A sequential binomial sampling system (Glance 'n go) has been developed to make decisions about control of greenbug, Schizaphis graminum (Rondani), and other cereal aphids on winter wheat in Oklahoma. Improvements to this sampling plan are underway to include parasitoid sampling to refine the decision thresholds. Because winter wheat is grown during the coldest months of the year, winter ecology of the primary parasitoid, Lysiphlebus testaceipes (Cresson), should be incorporated. This study examines oviposition by L. testaceipes at temperatures common during winter months in Oklahoma. Functional responses by L. testaceipes on greenbug were measured at seven temperatures (14, 12, 10, 8, 6, 4, and 2° C) during a 24 hour period (12 hr Light : 12 hr Dark). At each temperature, varying densities of greenbugs were exposed to individual L. testaceipes females. Over 200 L. testaceipes females were ultimately evaluated. All greenbugs were dissected 3-4 days after exposure. At temperatures below 8° C, most of the parasitoids failed to parasitize greenbug hosts, but L. testaceipes was observed to parasitize greenbugs at temperatures as low as 4° C, well below the developmental threshold temperatures of both S. graminum and L. testaceipes. Incorporation of these results into biological control programs of greenbug and other cereal aphids are discussed.