Certain factors affecting colonization of Ponderosa pine by Ips confusus (Leconte) (Coleoptera : Scolytidae) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9306t2767

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  • The purpose of this study was to study in some detail host factors which influence the population dynamics of bark beetle. The dissertation objectives were to ascertain the applicability of utilizing osmotic pressure values and relative turgidity values of phloem tissue as indicators which reflect upon the physiological profile of the tree; to examine the function of a blue-staining fungus in the bark beetle infested tree syndrome; to investigate dissimilitudes in host physiology and how they correlate to beetle colonization. The osmotic pressure (o.p.) of the phloem sap in six ponderosa pine were followed from May through September. The initial May values for the three high oleoresin exudation pressure (o.e.p.) trees (greater than 166 p.s.i.) were in excess of 11.2 atmospheres, while the three trees with a zero o.e.p. showed an o.p. of 8.4 atmospheres or less. This distinction between the o.e.p. categories was not maintained throughout the ensuing four months. The highest o.p. values were observed in July for five of the six trees. Relative turgidity and phloem thickness measurements did not appear applicable as indicators of the tree's physiological profile. The former measurement was unacceptable due to the large variation in water soluble phloem materials. The latter indicator appeared limited in applicability due to the large variance between trees; however, certain intraspecific trends were established. Inoculation studies with the blue-staining fungus Ceratocytis ips indicated that the microorganism was aiding colonization and brood development in no other way than through reducing moisture movement and oleoresin exudation in the outer sap wood. Laboratory studies revealed that Ips confusus prefer higher moisture gradients when the ambient humidity of the ventilating stream in the laboratory olfactometers was low, e.g., 0% R.H. Interference in threshold studies of the attractant principle was avoided by conducting all tests in atmospheres saturated with water vapor. Five carbohydrates, including maltose, fructose, sucrose, glucose and potato starch, were examined as dietary supplements for enhancing the pheromone synthesis. Data were not conclusive but they suggested that glucose was prominent as a dietary supplement. With the exception of starch, those sugars containing a glucose moiety showed some effect as a dietary supplement. Subsequent studies on nutritional requirements failed to show that fat soluble materials are a requisite for pheromone synthesis. Response dissimilitudes in field olfactory studies were related to the osmotic values of the expressed phleom sap. Trees with phloem tissue low in non-electrolytes appeared to represent a substrate which was less favorable as a dietary media for pheromone synthesis. This observation was demonstrated experimentally by severing the sieve elements in ponderosa pine for various periods of time. Olfactometers baited with billets distal to a one-month and one-year-old girdle were preferred by responding Ips confusus. These results were paralleled by comparisons of billets from above and below the site of an infection by Cronartium harknessii. Dissimilitudes in response patterns were also related to the various heights of the stem from which the billets were obtained. Consistent in two separate studies, male laps confusus forced into billets from the upper stem portion were capable of eliciting a greater response than males in the butt portion. The apparent level of pheromone synthesis by male Ips confusus could not be related to the thickness of the phloem. No effect on pheromone synthesis was apparent when beetles were forced to feed in tissue 0.22 inches thinner than their average dorsal-ventral dimension. Exuding oleoresin from the exposed surfaces of the billets exhibited a marked interference in field olfactory studies. This interference was reduced by washing the exposed xylem with ethyl alcohol and then applying a coat of molten paraffin.
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