Seasonality of codling moth, Cydia pomonella L. (Lepidoptera: Olethreutidae) in the Willamette Valley of Oregon : role of photoperiod and temperature

Graduation date: 1990The seasonality, relationship of temperature and\ud photoperiod to growth and post-diapause development, and\ud overwintering behavior of codling moth, Cydia pomonella L.,\ud (Lepidoptera: Olethreutidae) were studied over a three year\ud (1986-1989) period. The developmental threshold varied from\ud a low of 9.66°C for the second instar to a high of 14.23°C\ud for the fourth instar. A general threshold of 11.06°C was\ud determined from larval to adult stage for both sexes\ud combined. Data derived from the developmental study\ud suggested that both temperature and photoperiod had an\ud influence on development. Fastest development occurred at\ud elevated temperature (28°C) and moderately long photoperiod\ud (LD 14.75:9.25), although the rate declined beyond 30°C.\ud Thermal requirements for development were 441.26 thermal units (TU) from larvae to adult. There were no significant\ud differences between the two sexes in the total number of\ud thermal units required.\ud The critical photoperiod for diapause induction in\ud codling moth populations from the Willamette Valley\ud (latitude 44.5°N) was LD 15.5:8.5 at 24°C. Diapause in this\ud insect was induced in all larval instars, although it\ud appeared that the third and the fourth instars were slightly\ud more sensitive than the other instars. Temperature also had\ud an influence on diapause induction. The incidence of\ud diapause induction was higher under fluctuating temperatures\ud than at constant temperatures.\ud The codling moth populations from the Willamette Valley\ud began to come out of diapause in the third week of March\ud when photoperiod was 13-13.5 hours. Laboratory experiments\ud also showed that 13.41 hours of light was the critical\ud photoperiod for diapause termination. Approximately 39.4%\ud of the first generation and almost all of the second\ud generation larvae entered diapause. The incidence of\ud diapause in the first generation, when the outdoor weather\ud was close to diapause-averting environment, suggested the\ud existence of a univoltine population of this insect in the\ud Willamette Valley.\ud In the Willamette Valley codling moths overwinter as\ud diapausing third, fourth, and fifth instar larvae. The\ud relative proportions of these instars were: 3-21% in third, 10-11% in fourth, and 61-77% in fifth. However, all the\ud third instar larvae were parasitized, and it appears that\ud only the fourth and the fifth instars can overwinter and\ud emerge as adults in the following season. Incorporation of\ud this information into codling moth phenology models should\ud improve the performance of these models