Graduate Thesis Or Dissertation

 

Thelytokous and dioecious populations of Phenacaspis pinifoliae (Fitch), (Homoptera : Diaspididae) Public Deposited

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  • Two populations of the pine needle scale, Phenacaspis pinifoliae (Fitch), were studied. One population was located in Corvallis, Oregon, and the other population was located near Santiam Pass, Oregon. Both populations were feeding on Pinus contorta. The Corvallis population was unisexual, univoltine, and over wintered as both eggs and adult females. The life cycle and seasonal history of the Corvallis population were compared with those described in the literature for bisexual populations in Saskatchewan and Connecticut and differed strikingly from both of these. The Saskatchewan population was univoltine and overwintered as eggs only. The Connecticut population was reported to be bivoltine and overwintered only as eggs. The Santiam population was bisexual. No data were obtained concerning the number of generations or overwintering form of the Santiam population. Cytological comparisons of the Corvallis and Santiam populations Redacted for privacy were made through microscopic examination of unhatched embryos. Embryos from the unisexual Corvallis population showed eight chromosomes per cell. Embryos from the bisexual Santiam population showed either four or eight chromosomes per cell. Since the Corvallis population consisted of females only, it was apparent that female P. pinifoliae were diploid and the males haploid. Evidence was presented to show that the bisexual Santiam population probably reproduces by the diaspidid method, in which the males are haploid and lack heterochromatin. It was assumed that the closely related unisexual Corvallis population utilizes a similar method of reproduction. Finally, mature females of the two populations were compared morphologically. Significant differences associated with the pygidium were found between the populations. It was decided that for the present the two populations should retain their conspecific status even though differences were found.
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