Lysiphlebus testaceipes (Cresson) is a freezing intolerant parasitoid of many aphid species including greenbug, Schizaphis graminum (Rondani). Many freezing intolerant species can enhance their cold hardiness by supercooling their body fluids below the normal freezing point and avoiding a lethal freezing of their tissues. Adult and immature (mummies) L. testaceipes parasitoids with fine thermocouples attached to them, were cooled in insulated test tubes that were covered with dry ice. Supercooling points were measured by recording temperature every 0.5 seconds until parasitoid fluids spontaneously froze, as indicated by a significant temperature spike. Parasitoid mummies and greenbug hosts were observed to have similar minimum supercooling points with little variation (mummies: mean=-26.4º, SE=0.17, Range 24.5º to 27.8º C; greenbug: mean=-26.2º, SE=0.14, Range 25.8º to 26.8º C). Adult parasitoids (< 12h post emergence, unmated, naïve females), were observed to have a minimum supercooling point that was also similar to mummies and their greenbug hosts, but with more variation (mean=-26.2º, SE=0.31, Range 22.3º to 27.5º C). Male adult parasitoids displayed similar results. Adult parasitoids taken from the stock colony, with age unknown were highly variable in their supercooling ability (males: (mean=-20.3º, SE=1.32, Range 5.4º to 27.3º C; Females: (mean=-22.5º, SE=0.61, Range 9.3º to 26.7º C). Specimens with known supercooling points were analyzed to determine whether depletion of fat body lipids or some other difference in chemical composition might be responsible for the greater observed variation. These results are forthcoming and will be discussed in the poster.
Species 1: Hymenoptera Aphidiidae Lysiphlebus testaceipes
Species 2: Homoptera Aphididae Schizaphis graminum (greenbug)
Keywords: lipids, cold hardiness
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