Graduate Thesis Or Dissertation
 

The effect of light intensity on Douglas-fir foliage quality : survival and development of Western spruce budworm

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dn39x4542

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  • Foliage from Douglas-fir(var. glauca) seedlings grown under two light intensities was bioassayed to examine palatability to the western spruce budworm (Choristoneura occidentalis Free.). Samples were collected in Fall, Winter and early Spring to identify seasonal changes in host foliage, as evidenced by the response of spruce budworms. Fall collected foliage had little effect on budworm survival and fitness. Winter and Spring foliage grown in full sun produced significantly greater larval and pupal mortality, longer larval development times, lower pupal weights and reduced fecundity. These results indicate the level of Douglas-fir foliar defenses was influenced by season and light intensity. I suggest that the available carbon and energy resources decline in the shade due to lower photosynthetic activity. This in turn reduces the biosynthetic substrates needed for the costly production of defensive chemicals, and therefore, increases the foliage palatability to spruce budworm. The dynamics of seasonal sinks for carbon and energy compounds may determine when and to what extent fol jar defenses are synthesized.
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