Graduate Thesis Or Dissertation

 

Influence of temperature and photoperiod on the developmental biology of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera:Tortricidae) Público Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bg257j249

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  • Developmental thresholds and thermal unit (degree day) requirements for eggs, different larval instars, pupal stage and preoviposition period were determined for the obliquebanded leafroller (OBLR), Choristoneura rosaceana (Harris). Separate thresholds and degree day requirements were determined for males and females, but differences between the sexes were not significant. However, there were significant differences among the developmental thresholds for different larval instars. A total of 700.1 degree days were required for the complete life cycle (egg to egg). Diapause in the obliquebanded leafroller was induced and expressed in the larval stage. Both temperature and photoperiod played a distinct role in diapause induction, maintenance and termination. Under laboratory conditions, the critical photoperiod for diapause induction was between 14-15 hours of light per 24 hr period. Constant high temperatures of 28°C and above and fluctuating temperatures (12:12 cycle) with high temperature of 25°C and above also induced diapause. First and second instar larvae were the only stages sensitive to diapause induction. Diapause was mainly expressed in the third and fourth instars. Under Wilimette Vally conditions, 19-22% of the first generation larvae entered diapause during the second week of July, and almost all second generation larvae entered diapause. Diapause in the first generation was expressed mainly in third and fourth instars, while the second generation larvae expressed diapause In second and third instars. The diapause in the field was initially maintained by declining photoperiod in the fall months, then by falling temperatures in late fall and winter months. It was terminated during spring months in a bimodal fashion in response to increasing temperatures. A phenology model for predicting adult emergence, oviposition, and egg hatch based on time-temperature relationships was developed. The model was validated during 1984.
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