The objectives of this study were to define the life history of the lodgepole terminal weevil (Pissodes terminalis Hopping) in the Cariboo Forest Region, to quantify the magnitude of damage resulting from weevil attacks, and to determine if P. terminalis activity was associated with measurable tree and stand parameters such as leader dimensions and density. Four study plots in juvenile lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) stands near Riske Creek, B. C. were selected to provide data on the biology of the lodgepole terminal weevil. In each plot, weekly collections of 10 weevil-attacked terminal shoots were made from June 3 to August 29, 1980, and monthly collections were taken during September through November. All leaders were dissected and the numbers of each P. terminalis life stage and associated predators/parasitiods were recorded. Seventy-one survey plots in lodgepole pine stands between 8 and 29 years of age throughout the Cariboo Forest Region were assessed for weevil activity. Each survey plot contained 25 trees over 2 metres in height, and each tree was measured for height, diameter at breast height, leader length, and basal leader diameter. Stand age, elevation, density, and all weevil attacks (including year of attack and type of resultant stem deformity) were also recorded. Weevil development appeared to be fairly uniform regardless of stand density and/or elevation; therefore, the data from all four biology study plots were combined to construct a life history diagram. In 46% of the survey plots one or both of the leader dimensions was significantly greater for attacked trees as compared to unattacked trees. In 28% of the plots attacked trees were either significantly taller or larger in diameter. Over 50% of the trees in stands of less than 4,000 stems per hectare had been attacked by P. terminalis at least once. Severe stem deformities such as forks and "stag-heads" comprised a larger proportion of damaged trees in the lower stand density classes. Weevil activity appeared to be higher in 1980 than in 1979. It was concluded that the lodgepole terminal weevil is currently a widely distributed and serious pest of young lodgepole pine stands in the Cariboo Forest Region. Given the present levels of weevil-caused damage as well as the possibility of future attacks, it was recommended that the activity of P. terminalis be considered when silvicultural practices such as juvenile spacing are undertaken in these stands. / Forestry, Faculty of / Graduate

Fraser oats were used to study populations of cereal aphids in 1972,1973 and 1974. The most commonly found species were Macrosiphum avenae (F.) (the English grain aphid), Metopolophium dirhodum (Wlk.) (Rose-grain aphid) and Rhopalosiphum padi (L.) (Oat bird-cherry aphid). Aphid density was highest in 1972, lower in 1973 and lowest in 1974. Generally M. avenae had the highest population with M. dirhodum slightly lower. Rhopalosiphum padi was found infrequently with low numbers. Fecundity trials, used to examine whether the difference between numbers of species was because of a difference in fecundity, did not substantiate field results but instead indicated that R.padi should have produced the highest population. Differences were not found in the population dynamics when the oats were planted in solid blocks instead of rows. A one month delay in the planting date did not change the total aphid population but did result ira higher proportion of M. avenae than found in any other plot. Coccinellid numbers in two out of the three years were considered negligible. In 1972 rain was thought to destroy many coccinellid before they reached large enough numbers to greatly affect the aphid population. No direct samples were taken of hymenopterous parasites but any found were collected and identified. Water experiments were conducted to study the effect of water on the fecundity of R. padi. It. was concluded - that R. padi definitely preferred wet conditions. Temperature and rainfall readings were used to show the effect of weather on aphid numbers. Weather was shown to be a major regulatory factor in the population dynamics of cereal aphids. Considerations were made for aphid mortality caused by sparrows. / Land and Food Systems, Faculty of / Graduate

Cherry leaf roll virus, as a nepovirus with a bipartite genome, can be genetically analysed by comparing the properties of distinct 'parental' strains and the pseudorecombinant isolates generated from them. In the present work, the elderberry (E) and rhubarb (R) strains were each purified and separated into their middle (M) and bottom (B) components by sucrose gradient centrifugation followed by near-equilibrium banding in cesium chloride. RNA was extracted from the separated components by treatment with a dissociation buffer followed by sucrose gradient centrifugation. Extracted M-RNA of E-strain and B-RNA of R-strain were mixed and inoculated to a series of test plants as were M-RNA of R-strain and B-RNA of E-strain. New local lesion types in Nicotiana clevelandii induced by these heterologous RNA combinations were passaged three times through local lesions on N. clevelandii in order to generate pure pseudorecombinant stocks. M-RNA determined serological specificity, the distribution of virus particle components, systemic symptoms in N. clevelandii and N. tabacum cvs. Samsun and Xanthi as well as the local and systemic symptoms in Chenopodium amaranticolor and C. quinoa. B-RNA determined the ability to induce systemic symptoms in Gomphrena globosa and the type of local lesion in N. clevelandii. When the procedure used for originally generating the pseudorecombinants from the parental strains was applied to the pseudorecombinant isolates themselves, isolates were obtained in the predicted manner that were identical to the original parental E- and R-strains. / Land and Food Systems, Faculty of / Graduate

There are three natural openings in a mature sugarbeet fruit which serve as avenues of entry for microorganisms: 1) the basal pore which contains dried parenchyma and vascular tissue and is the point where the flower was connected to the stalk; 2) the apical pore where the style was inserted; and 3) the peripheral zone of dehiscence where the operculum separates from the fruit cavity wall during germination. The apical pore was first described in this study. Scanning electron microscopy of the naturally infected fruits showed, for the first time, hyphal penetration through both the basal pore and the peripheral zone. Examination of sugarbeet flowers artificially infected with Phoma betae also showed fungal penetration through the apical pore. Dense hyphal growth was associated with stigmal lobes and ungerminated pollen grains. Fungal growth apparently was stimulated by excretions from the stigma. Penetration of the fruit cavity wall and the operculum would render the fungus inaccessible to protectant fungicides and explains why the most successful seed treatments for P. betae have included volatile mercury fungicides or seed soak in thiram. Such treatment allows direct contact between the toxin and the pathogen. / North Dakota State University (NDSU) / Kiesling, Richard L.

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