Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 125-127).

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 39-41).

Investigations were carried out to determine factors which permit the development of outbreaks of the hemlock saw-fly, Neodiprion tsugae Midd., within restricted portions of a wide range. This was done through the observation of populations in the field, supported by laboratory studies designed to show that certain influences are important. Populations were found to be directly proportional to the relative humidity within the tree crown. Epidemic populations occurred only where hemlock made up at least 50 percent of the stand and where the average relative humidity within the crown did not fall below 50 percent for any period of a month during the summer. Relative humidity was governed by stand composition, stand density, age, elevation, and exposure. The relative humidity was inversely proportional to the amount of Douglas fir present in the stand. Western red cedar in amounts up to 30 percent increased the relative humidity where hemlock was present as a co-species. Stand density affected humidity to the extent, that the relative humidity was higher in open stands where crowns were dense. Factors contributing to this appear to be: profuse ground cover which contributed to evaporation: the dense foliage within the tree crown increasing transpiration but retarding air circulation: large crowns extending to the ground cover providing a protective leaf shelter over the entire area, thus preventing the escape of moisture. Maximum populations were recorded on sites of medium quality, poor sites producing trees of insufficient crown density to maintain humidity. Outbreaks have been confined generally to open hemlock regeneration with large, dense crowns along the shoreline or near tidewater and to similar stands inland above the 1500-foot elevation. Relative humidity was shown to be of direct significance to egg-laying, hatching, and movement and survival of small larvae. The sex ratio appeared also to be influenced by population density, the percentage of males varying directly with population. The fecundity varied inversely with population density. / Science, Faculty of / Zoology, Department of / Graduate

Differences in egg colour among European sawfly species were known for many years, but no use of the information in basic taxonomic work was attempted, and there was little application in practical keys or identification tables. The egg colours of North American sawflies were unstudied, except for an occasional, casual reference to the colour in an individual species. The work reported in this thesis represents the first attempt to study sawfly egg pigmentation in an objective manner, and to apply the findings to taxonomic research, as well as to provide data for use in identification aids. The analytical methods were adapted from other fields, but it was necessary to carry out tests to make certain that confidence could be placed in the results, because the conditions in the present study were not identical to those in the work from which the methods were derived. [...]

Sawflies, as relatively primitive members of the highly specialized order Hymenoptera, have always been regarded with interest. Trends towards parasitism and social habits have been viewed as thought-provoking links to the parasites and ever-popular grouping of bees, ants and wasps. [...]

Thesis (Ph. D.)--University of Illinois, 1920. / "Contributions from the Entomological laboratories of the University of Illinois, no. 69." Bibliography: p. 135-140.

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