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

Overwintering larvae of the goldenrod gall fly Eurosta solidaginis beg in to freeze at temperatures above - 10-degrees-C. The initiation of f reezing at relatively high subzero temperatures may involve multiple i ce nucleation mechanisms to protect the insect from lethal intracellul ar freezing. In spring, the insect changes the mode of its cold-harine ss from freeze-tolerant to freeze-susceptible type, with the metamorph osis from larva to pupa. The change is accompanied by a lowering of th e supercooling points (spontaneous freezing points) and an increase in the resistance to inoculative freezing. The present study demonstrate d that the change in cold-hardiness accompanied by puparium formation is artificially induced by 20-hydroxyecdysone treatment. In the beginn ing of the puparium formation, the insects lowered their supercooling points and lost their freeze tolerance, becoming resistant to inoculat ive freezing. At 25-degrees-C, the serial changes were completed withi n a week of the hormonal treatment.