DIFFERENCES IN THERMAL REQUIREMENTS FOR DIAPAUSE TERMINATION IN TWO WESTERN CHORISTONEURA SPP. (LEPIDOPTERA: TORTRICIDAE)

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Abstract
Storage of diapausing larvae of Choristoneura viridis and C. occidentalis at low temperature (2°C) appeared to be sufficient stimulus to terminate diapause. Reactivation at 25°C occurred sooner and was more synchronous with longer storage at 2°C. Highest survival was obtained after storage of 20 to 22 weeks for both C. viridis and C. occidentalis. Intraspecific and interspecific reactivation rates were compared by analysis of covariance, using the model ln Y = a + B ln X , where Y = larval emergence in days at 25°C and X = storage in weeks at 2°C. Intraspecific sex differences were not significant, indicating that protandry observed in this laboratory in both species must be due to some other factor. C. viridis had substantially less stringent thermal requirements for diapause termination than C. occidentalis. Diapause in the two species is discussed.