A COMPARISON OF INJURY AND SURVIVAL OF LARVAE OF CEPHUS CINCTUS NORT. AFTER INTRACELLULAR AND EXTRACELLULAR FREEZING

Abstract

Extracellular freezing of larvae of the wheat stem sawfly, Cephus cinctus Nort., was produced at −2.5 °C by a new method. Slow further cooling to −10, −15, or −20 °C added to extracellular ice with no intracellular freezing. Other larvae that were supercooled to and frozen at −10, −15, or −20 °C froze intracellularly. Comparisons of the effects of these two types of freezing were therefore possible at equivalent temperatures. Level of activity after freezing was used as the criterion of injury.Intracellular freezing was more injurious than extracellular freezing at −15 and −20 °C, but not at −10 °C. Injuries, as well as differences in injury due to type of freezing, decreased gradually to insignificance above −10 °C. Although larvae frozen extracellularly held an initial advantage over those frozen intracellularly, survivors of the latter group retained their vitality better, probably because they lost weight more slowly.Differences in injury and in activity level after freezing at −15 and −20 °C were insufficient to justify the use of freezing site (intracellular or extracellular) as a principal basis for explaining freezing injury. The same conclusion applies to ice crystal size and configuration, which differed vastly in the two types of freezing.These conclusions depend on whether freezing was actually intracellular or extracellular as represented. Strong evidence is presented that freezing was in fact as specified.