viii, 132 leaves : ill. photos, tables ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Entomology, 1978

x, 145 leaves : ill., tables, map graphs., photos ; 31 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1980)--University of Adelaide, Dept. of Entomology, 1980

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No description available.

Tobacco rattle virus (TRY) and trichodorid vector nematodes were found to be widespread in bulb growing areas in The Netherlands. Indications, obtained from pot bait tests, that associations between serotypes of tobacco rattle virus and Paratrichodorus and Trichodorus vector species occurred were confirmed in bait tests using individual trichodorid nematodes. Whereas different Paratrichodorus vector species each transmitted a serologically distinct TRV-isolate, different Trichodorus vector species transmitted serologically indistinguishable TRV-isolates. It remains to be studied whether a particular Trichodorus species is able to transmit all isolates serologically indistinguishable from the one with which it was naturally associated. A TRV-isolate transmitted by T. cylindricus from Scryne, Scotland and isolates transmitted by P. teres from Julianadorp, The Netherlands were considered anomalous TRV-isolates as they serologically resembled pea early-browning virus but had RNA-1 sequences typical of TRV. Virus-free P. pachydermus from Scotland and from The Netherlands acquired and subsequently transmitted TRV-isolates originally obtained from bait-plants infected by P. pachydermus from Scotland or The Netherlands. They failed to transmit a serologically similar isolate obtained from an infected potato tuber. Virus-free P. pachydermus did not acquire and transmit a pseudorecombinant TRV-isolate with the RNA-2 from a non-transmissible isolate, but efficiently transmitted a pseudorecombinant isolate in which the RNA-2 was derived from a efficiently transmitted isolate. This indicated that transmissibility is most likely determined by the virus coat-protein. Transgenic tobacco plants, expressing TRV coat-protein were resistant to mechanical inoculation but susceptible to nematode transmission of the virus. A possible low level of coat-protein expression in the roots could not fully explain this result as the nematodes also transmitted TRV directly to detached leaves of such transgenic plants.

Ph.D. (Botany) / Please refer to full text to view abstract

M.Sc. / The extent of economic damage caused to the cotton variety Acala 1517/70 by the feeding activities of Tetranychus cinnabarinus (Boisduval) has been studies at the Loskop Research Station, situated in the Transvaal Middleveld. Special attention is given to the relative importance of the occurrence of spider mite infestations during the various stadia in the development of the cotton plant. the common method by which the extent of mite infestations is calculated, namely the conversion of adult female counts to female-days / leaf is used, and this unit of measure is compared to the percentage of leaf surface area over which visible damage extends (trial 1) as well as to the actual damaged leaf surface area. An index system is used to determine the percentage of leaf surface area over which visible damage extends (trial 1). The effectiveness of this procedure in determining the actual damaged leaf surface area is found to be sufficient, and is recommended as it appears to be a rapid and accurate method for evaluation during field trials. In accordance with quoted literature it is determined that the regression of both the leaf surface area over which damage extends (as determined by the index system as described) and the actual damaged leaf surface area against the female-days I leaf at a specific stage, are highly significant. It is confirmed that the use of either the percentage of leaf surface area over which damage extends or the actual damaged leaf surface area is valid. A method that is based on the use of female-days) leaf, but which in addition takes into account the stage (in days after planting) at which a particular spider mite count has been present is developed for the purposes of this study. It has been confirmed that this particular unit (damagedays IleaO has practical application value. It is pointed out that even in the early stages of population buildup there exists a highly significant relationship between both the femaledays / leaf and the damage-days Ileaf,and the yield masses. Significant reductions of up to 16 percent in yield were found in spite of the fact that notable spider mite infestations had not occurred prior to the flowering peak. By taking the value of the cotton yield into account and comparing it with the cost of control, an economic evaluation of the specific treatments is made. The following important conclusions were reached: • The confirmation of the profitability of applying an acaricide (triazophos) as soon as the first signs of a red spider mite infestation is discovered. • the irrelevance of programme spraying regardless of the infestation present, • the decrease in relative importance of red spider mide infestations in the later stages of the development of the cotton plant, and • the probability of spider mites affecting both the yield mass and quality if heavy infestations prevail after 19 weeks (133 days) after planting.

M.Sc. (Biochemistry) / Please refer to full text to view abstract

In the Swaziland lowlands, biological control of the citrus pest red scale, Aonidiella aurantii (Mask), has been consistently unsuccessful although it is successful in middle altitude regions. However, recent cases of resistance to organophosphate insecticides elsewhere in southern Africa, make it important to reconsider biological control of red scale in the lowlands. Should similar resistance be evolved in this region, the pest could be controlled only by natural means together with oils. This account attempts to answer questions about the natural control of a red scale population in the lowlands, by examining data collected between 1972 and 1975. The population was continuously breeding with overlapped generations. It consisted of three sections, on leaves, twigs and fruit, having different rates of reproduction, development and mortality. These sections are considered separately but that on leaves, being relatively unimportant, is largely ignored. The generation mortality is estimated in the sections on twigs and fruit and related to climatic and biotic indices. The causes of seasonal and between-years variation in the sections on twigs and fruit are elucidated. The effectiveness of each kind of natural enemy is examined and the factors affecting natural enemy numbers are investigated. The question of population regulation is discussed. Differences in mean infestation levels in middle altitude and lowland regions are explained in terms of different rates of reproduction and mortality.

After a brief introduction, the species of Citrus on which the investigations were carried out are mentioned. This is followed by an account of the methods of collection used, and a discussion of their relative merits. The main method used was that in which the trees were fumigated with hydrocyanic acid gas, and the insects falling from the trees were taken up on sheets. The location of the areas where collections were made are then given. An annotated list of the species taken by the fumigation method follows, and the numerical data obtained at the same time regarding the species present is given in an abbreviated form and discussed. A more detailed discussion of the relative abundance of the species is then undertaken. The discussion of the ecology of the insects commences with the insects listed according to their activities, so far as known, and an account of five trees of striking faunal differences is given. A broader discussion of citrus ecology is then given, based on the data previously presented; this ends with a short reminder of the inherent 'oneness' of the insect with its environment.