Certain biotic factors influencing the invasion and survival of the Douglas-fir beetle Dendroctonus pseudotsugae Hopkins (Coleoptera : scolytidae) in fallen trees Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pc289m354

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  • Factors considered were phloem moisture, sour-phloem (which may be furthered by the presence of ample phloem moisture), oleoresin of the host, and the presence of unmated female beetles in suitable host material. Levels of phloem moisture present in variously prepared logs in the field ranged from about 100 to upwards of 250 percent of dry weight. Observation of such host material during the main season of beetle flight supported the conclusion that the Douglas-fir beetle attack volume was not related to moisture level. Experimentation with short logs which had either been soaked or not soaked verified this conclusion; at the same time it was demonstrated that Gnatho-trichus sp., Dryocetes autographus (Ratzeburg), and Hylastes nigrinus (Mannerheim) were attracted to the logs which had been made wetter, Within the range observed in the field, moisture level did not influence brood success. The case where moisture implements an air-tight seal, its effectiveness being indicated by sour-phloem development, is an exception. Sour-phloem is a decay condition which develops under anerobic circumstances. Moisture is viewed as an accessory to its formation in that it implements an air-tight seal of intact bark. At the time of attack only incipient sour-phloem was present in various of the pieces of host material in this study and in this stage of development did not influence attack by the Douglas-fir beetle. Sour-phloem, however, was associated with restricted brood development, more likely as an indicator of low oxygen levels rather than as a detrimental habitat factor in itself. Minimal oleoresin exudation pressures (1 to 17 pounds per square inch) were measured in fallen Douglas-firs which, observed through the attack season and later analyzed, were seen to have an appreciable number of incidences where oleoresin was judged to have interfered with beetle entry. Similarly, brood size and success was determined to have been limited by oleoresin. The introduction of unmated female beetles was seen to so strongly prompt other females to attack a log that it not only affords an explanation of how beetles are attracted en masse but also explains why there can be beetle indifference to otherwise suitable host material which happens to lack prior entered females. MaIe beetles are also attracted by the unmated females. Beetle response is to odor; air blown over a properly treated and hidden log attracted beetles. The intensity of mass attack relates to the intensity of the earliest attack. The species demonstrates a gregarious habit which, it is argued, would facilitate mating, shatter the tree's defensive oleoresin exudation, enable mass tunneling of the inner bark so that adequate ventilation would be afforded the brood, and serve to insure that it will place economic demand on the population of its host. The strong displacement effect of logs having female beetles warrants strong consideration when studies are made seeking to identify attractive factors that belong to the host per se. When forced entry of females was made into irregular host material, it received subsequent attack. Intensity of attack, as judged from the experiment of one season, is independent of host felling dates when the range of these is less than a year. Air temperature observation in connection with the studies provided insight with regard to the predicability of attack in suitable host material as spring warming continued.
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  • description.provenance : Approved for entry into archive by Katy Davis(kdscannerosu@gmail.com) on 2014-05-12T23:20:43Z (GMT) No. of bitstreams: 1 HendricksonWilliam1965.pdf: 10094282 bytes, checksum: b77742fc1dbbcd32d43c5948380c93b2 (MD5)
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