The Effect of Prior Chilling Exposure on Supercooling Ability and Developmental Success in Third-Instars of Eurosta solidaginis (Diptera: Tephritidae)

摘要

The ability to initiate freezing at elevated subzero temperatures is deemed an important adaptation in freeze-tolerant insects, as this phenotype allows them to avoid potentially lethal flash freezing and to conserve both body water and stored energy. We investigated the effects of recent freeze exposure on the subsequent supercooling points (SCPs) of overwintering freeze-tolerant larvae (third instars) of the dipteran Eurosta solidaginis Fitch. This large data set also allowed us to characterize the distribution profile for SCPs and the potential impact of body size on this parameter. Larvae having recent freeze exposure maintained their seasonally elevated SCPs, with one group, 2 d postfreeze, showing a significant (P < 0.05) rise in their SCPs. Larvae that experienced supercooling to -7 degrees C did not show a significant (P > 0.05) rise in their SCPs. Despite differences in total body water content among larvae of varying body sizes, there was not a significant (P > 0.05) relationship between body mass and the initial SCP values, but there was an absence of normality (negative skewing) in the SCP values. Larvae completing their life cycles had SCPs equivalent to values for larvae that failed to complete the life cycle. Our findings demonstrate actions of potent ice nucleators such that the response is maintained and possibly enhanced following a recent freeze event. Ice nucleation in Eurosta larvae negates the impact of variation in water content, but individual variation in SCP does not have a survival consequence when gauged under laboratory conditions.