LOSS OF ICE-NUCLEATING ACTIVITY AND AVOIDANCE OF INOCULATIVE FREEZING WITH PUPARIUM FORMATION INDUCED BY 20-HYDROXYECDYSONE IN EUROSTA-SOLIDAGINIS (DIPTERA, TEPHRITIDAE)

Overwintering larvae of the goldenrod gall fly Eurosta solidaginis begin to freeze at temperatures above - 10-degrees-C. The initiation of freezing at relatively high subzero temperatures may involve multiple ice nucleation mechanisms to protect the insect from lethal intracellular freezing. In spring, the insect changes the mode of its cold-hariness from freeze-tolerant to freeze-susceptible type, with the metamorphosis from larva to pupa. The change is accompanied by a lowering of the supercooling points (spontaneous freezing points) and an increase in the resistance to inoculative freezing. The present study demonstrated that the change in cold-hardiness accompanied by puparium formation is artificially induced by 20-hydroxyecdysone treatment. In the beginning of the puparium formation, the insects lowered their supercooling points and lost their freeze tolerance, becoming resistant to inoculative freezing. At 25-degrees-C, the serial changes were completed within a week of the hormonal treatment.