FORECASTING PHENOLOGY OF ORTHOSIA HIBISCI GUENÉE (LEPIDOPTERA: NOCTUIDAE) IN BRITISH COLUMBIA USING SEX-ATTRACTANT TRAPS AND DEGREE-DAY MODELS

Emergence, oviposition, and seasonal flight activity of adult, speckled green fruit worm, Orthosia hibisci Guenée (Lepidoptera: Noctuidae), were monitored during 1991 and 1992 in a mixed block of McIntosh and Spartan apple trees at Summerland, British Columbia, to establish relationships between the phenology of these events and degree-days (DD). Using air temperatures and a developmental threshold of 3 °C, median emergence of males was predicted most accurately (0–2 days) by starting DD summations on 1 March. Median emergence of females was predicted without error when first catch of a male in a trap baited with sex attractant was used as a population reference point (biofix) to start DD summation. Using a threshold temperature of 3 °C, observed cumulative emergence of females reached 50% at 63.5 ± 4.05 DD3 °C after biofix, similar to the laboratory-derived prediction of 61.3 ± 4.2 DD with a threshold temperature of 2.8 °C. Catches of males with sex attractant preceded oviposition, but female catches in light traps lagged behind oviposition, suggesting older females were being caught in light traps. The oviposition curve was linear and parallel to the cumulative curve of male catches with sex attractant. Oviposition began at 26.7 DD3 °C and reached 50% at 94.2 DD3 °C after biofix, respectively. Weibull equations fitted to observed cumulative catches with sex attractant, female emergence, and oviposition, combined with laboratory-derived DD models of egg and larval development, were used to predict phenology of O. hibisci and correlate it with flowering phenology of pome fruits. This study provides a basis for timing application of selective insecticides against O. hibisci based on first catch in a sex-attractant trap and DD summations.