Effect of cooling rate on the survival of larvae, pupariation, and adult emergence of the gallfly Eurosta solidaginis

Freeze-tolerant third instar larvae of the gallfly Eurosta solidaginis were cooled at 10, 5, 1, and 0.1 degrees C min-1 to -40 degrees C and then warmed to +5 degrees C at 1 degree C min-1. After cooling and warming the larvae were transferred to 21 degrees C and the survival of larvae, success of pupariation, and adult emergence were monitored at daily intervals in comparison to an uncooled control sample. The percentage emergences of flies from larvae cooled at 10, 5, 1, and 0.1 degree C min-1 and in the control were 7, 13, 37, 77, and 67%, respectively. A number of flies in each group emerged with malformed (unextended) wings and an unretracted ptilinum on the head capsule. The percentage emergences of normal flies at the four cooling rates and from the control were 3, 0, 17, 47, and 57%. At 48 hr after exposure all larvae in each treatment were alive. First mortality was observed between 48 and 72 hr after cooling and increased with time at each cooling rate. Mortality was apportioned into four phases of development: larva, pupariation, and early and late pupae. Mortality commenced earlier at the faster cooling rates; at 10 degrees C min-1, 37% of the sample died as larvae and a further 20% failed to complete pupariation, whereas at 0.1 degree C min-1, only 3% died as larvae and 97% formed a puparium.