Cold hardiness of the fly pupal parasitoid Nasonia vitripennis is enhanced by its host Sarcophaga crassipalpis

Abstract

Supercooling points (SCPs) and low temperature survival were determined for diapausing and nondiapausing larvae of the ectoparasitoid Nasonia vitripennis. Neither nondiapausing nor diapausing larvae could survive tissue freezing. The SCP profiles were nearly identical for nondiapause-destined (−27°C) and diapausing larvae (−25°C), but these values were not indicative of the lower limits of tolerance in either type of larvae: larvae were killed by chilling at temperatures well above the SCP. Diapausing larvae could withstand low temperature exposures 3–8 times longer than their nondiapausing counterparts. Low temperature survival was enhanced in diapausing and nondiapausing larvae by their encasement within the puparium of the host flesh fly, Sarcophaga crassipalpis: the LT 50s determined for nondiapausing and diapausing larvae enclosed by fly puparia were 2–3 times higher than values calculated for larvae removed from the puparia. Additional low temperature protection was gained through acquisition of host cryoprotectants during larval feeding: nondiapausing parasitoid larvae that fed on diapausing flesh fly pupae with high levels of glycerol were able to survive exposure to a subzero temperature 4–9 times longer than wasps reared on nondiapausing fly pupae that contained lower quantities of glycerol. Alanine may also contribute to the cold hardiness of N. vitripennis, as evidenced by the fact that larvae feeding on diapausing fly pupae both contained higher concentrations of alanine and exhibited greater cold hardiness. The results thus demonstrate that several critical features of cold hardiness in the wasp are derived from biochemical and physical attributes of the host.