Thesis (Ph. D.)--University of Adelaide, Dept. of Crop Protection, 1992. / Includes bibliographical references (leaves 170-189).

Thesis (Ph. D.)--University of Adelaide, Dept. of Crop Protection, 1996. / Includes bibliographical references (leaves 221-240).

Thesis (Master of Ag. Sc.)--University of Adelaide, 1959. / Typewritten copy. Includes bibliographical references.

Thesis (Ph.D.)--Michigan State University. Dept. of Crop and Soil Sciences, 2008. / Title from PDF t.p. (viewed on July 17, 2009) Includes bibliographical references. Also issued in print.

Thesis (M. Sc. (Botany))--Rhodes University, 2000.

No description available.

A greenhouse study was undertaken to investigate some relationships between nutrition of the host tree, Abies amabilis, as influenced by soil fertility and nitrogen fertilizers, and biology of the balsam woolly aphid, Adelges piceae (Ratz.). Seedlings were reared in two soil regimes - nutrient-deficient mineral soil and enriched humic soil. All trees were infested with aphid larvae, and observations made to determine the influence of soil fertility on the establishment rate of larvae on host trees. Subsequently, groups of 10 trees were treated with foliar nutrients, using ammonium nitrate and urea in various concentrations. The establishment rate of larvae on humic soil host trees was 2.5 times greater than on mineral soil trees. In addition, growth rate of the aphid population on humic soil trees was 37% greater than on mineral soil trees over a four week period. Soil fertility also influenced the life history of the insect. One foliar nutrient adversely affected the aphid population. Over a 10 week period, the aphid population on trees treated with 1% ammonium nitrate decreased by 23%, whereas the control population Increased 30.9%. It is postulated that this foliar treatment manifests its adverse effect primarily by inhibiting initial settling of larvae on the host trees. This inhibition may be related to fertilizer-induced alterations in the amino acid composition of feeding tissue. / Science, Faculty of / Zoology, Department 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

A new aphid virus, aphid lethal paralysis virus (ALPV), was isolated from laboratory-propagated Rhopalosiphum padi aphids co-infected with R. padi virus (RhPV). ALPV and RhPV were separated and ALPV was characterised in detail. Virions are isometric with a diameter of 26 nm, a sedimentation coefficient of 164 Sand a density in CsCl of 1.34 g/ml. Virions contain a 9.7 kb polyadenylated, singlestranded RNA and three major proteins with molecular weights of approximately 30 kilodaltons. By characterising RhPV further, two additional putative capsid proteins were found, an RNA poly(A) tract was detected and an RNA size of 10 kb was determined. A South African isolate of RhPV (RhPVoFs) was found to be serologically identical but physically distinct from a USA isolate. Complementary DNA was synthesized from RhPVOFS RNA and cloned into the plasmid vector, pBR322. This clone was used for the detettion of virus in aphids. ALPV and RhPV are serologically unrelated. ALPV is serologically distantly related to two insect picornaviruses, cricket paralysis virus (CrPV) and Drosophila C virus. No nucleic acid homology was detected between ALPV cDNA and CrPV by dot-blot hybridization. ALPV is serologically unrelated to seven other insect picornalike viruses. RhPV is serologically unrelated to any of the above mentioned viruses. ALPV and RhPV RNAs were efficiently translated in rabbit reticulocyte lysate into high molecular weight polypeptides, the sum of which exceeded the coding capacity of the genomes. Putative capsid precursor proteins of ALPV and RhPV were identified by immunoprecipitation. ALPV translation products were post-translationally cleaved as demonstrated in pulse-chase experiments and in experiments using a translation inhibitor. The efficiency of cleavage was concentration-dependent indicating the action of a protease. In parallel experiments with RhPV RNA, no evidence of post-translational cleavage was observed. In a survey of aphids collected in South Africa, ALPV and RhPV were detected in aphids from two major small-grain producing areas. Both viruses were found to naturally infect most of the cereal aphid species found in this country. ALPV and RhPV infections of R. padi resulted in a marked reduction in longevity and fecundity relative to uninfected aphids. Both viruses were found to be horizontally and vertically transmitted through aphid populations, and aphid host plants and aphid predators could be implicated in virus dissemination. ALPV and RhPV have many properties in common with each other as well as with insect and mammalian picornaviruses. Based on this data, it is proposed that ALPV and RhPV be classified into the picornavirus group (family Picornaviridae).

No description available.