The two principal objectives of this study were: (i) to estimate and compare net revenue associated with alternative pest management strategies for Virginia soybean producers, and (ii) to compare attractiveness of different pest management options when net revenue risk is considered in conjunction with the corresponding level of expected net revenue. The method used to complete the first objective was to modify 1983 Virginia Cooperative Extension Service soybean budgets to correspond with alternative pest management strategies and then compare the average net revenue of the alternatives. The method used for completing the second objective was to develop a simulation model of net revenue for a representative Virginia soybean farm using alternative pest management strategies. Probability distributions of net revenue were generated and then compared using stochastic dominance analysis. Results from the net revenue comparisons of both expected net revenue and net revenue risk suggest that producers would prefer strategies which incorporate an integrated pest management (IPM) approach to pest control rather than an approach which relies completely on pesticides. Since pesticide usage is associated with negative environmental effects, the IPM alternatives, which in general decrease pesticide usage, would be preferred from the social as well as the private viewpoint. / M.S.

Thesis (MSc)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The Mediterranean fruit fly (Medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) is well-known as a destructive pest of fruit worldwide. Various control methods have been used against this insect. The sterile insect technique (SIT) is used as an important and successful technological method for controlling or eradicating this pest in many countries. A key factor to successfully apply SIT is dependent on the availability of efficient and economical rearing methods. Artificial insect diets with low cost bulking agents have been of interest to many researchers. The present study investigated the use of locally available maize meal as a bulking agent in such diets. Maize meal is used for human consumption (in South Africa) and contains small amounts of protein. This makes the reduction of imported torula yeast as an ingredient of the diet and source of protein possible, thereby reducing the cost of the diet. The larval development of the Medfly reared on artificial diets was studied in small and large-scale tests. The effect of the diets on larval production was evaluated using pupal recovery, pupal weight, flight ability, sex ratio, fecundity and egg fertility. The results of the small-scale tests showed that the diet containing maize meal could be used to produce Medfly more economically than the standard Krige diet used by the ARC Infruitec-Nietvoorbij Research Institute at Stellenbosch. However, in large-scale tests the ingredients quantities of the diets used were not the same as those of small scale-tests. The cost of the modified larval diet was not reduced in large-scale tests. This was ascribed to the number of eggs used in the tests to produce one million of fruit flies. The maize meal with reduced number of eggs require more diet to produce one million flies therefore, making it more expensive and less viable. When similar amounts of eggs were used, the diet appears to be a suitable alternative as the result obtained was almost similar to those of the Krige diet. / AFRIKAANSE OPSOMMING: Die Mediterreens vrugtevlieg ("Medfly"), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) is wêreldwyd 'n skadelike plaag. Die steriele insek tegniek (SIT) het in baie lande 'n belangrike en suksesvolle manier geword om die plaag te beheer en uit te roei. Die belangrikste voorvereiste vir die suksesvolle toepassing van SIT is die beskikbaarheid van doeltreffende en ekonomiese teelmetodes. Meeste navorsers is geïntereseerd in kunsmatige diëte met 'n goedkoop vulstof. Hierdie studie is ontwerp om die gebruik van plaaslik beskikbare mieliemeel as vulstof te ondersoek. In Suid-Afrika word dit vir menslike gebruik aangewend en bevat klein hoeveelhede proteïene wat 'n vermindering van die ingevoerde torula gis moontlik kan maak, en sodoende die koste van die dieët kan verminder. Die ontwikkeling van Medfly larwes op kunsmatige diëte is bestudeer In kleinskaalse en grootskaalse eksperimente. Die invloed van die diëte op larwale produksie is evalueer deur gebruik te maak van van papie-ontwikkeling, papie-gewig, vliegvermoë, geslagsverhouding, volwasse voortplantingsvermoë en eiervrugbaarheid. Die resultate van die kleinskaalse toetse het aangetoon dat die mieliemeel dieët gebruik kan word om Medfly meer ekonomies as met die standaard Krige dieët, wat in die ARC Infruitec-Nietvoorbij navorsings instituut by Stellenbosch gebruik word, te teel. By die grootskaalse toetse was die koste nie laer nie. Dit word toegeskryf aan die aantal eiers wat gebruik is om 'n miljoen vlieë te produseer. Die mieliemeel dieët met 'n verminderde aantal eiers benodig meer dieët om 'n miljoen vlieë te produseer, wat dit duurder en minder lewensvatbaar maak. Wanneer soortgelyke hoeveelhede eiers gebruik was, het dit geblyk dat die dieët 'n opsie is, want die resultaat was soortgelyk aan dié van die Krige dieët.

Maize (Zea mays L.) streak virus disease (MSD) is the most important virus disease in Africa but farmers are unaware of its status. A project was initiated to assess the current status of MSD and to breed for its resistance. Four populations comprised of two BC1F1 and two F2 progenies developed by backcrossing and selfing the F1 progenies of two crosses between a donor line (CMl 202) and two susceptible lines (CMl 321 and CMl 384) were developed. Conventional and molecular marker assisted selection (MAS) methods were used to screen for resistance to MSD in each of the four populations. To facilitate unbiased comparison, separate screening nurseries were established for MAS and conventional screening. The objectives of the study were five-fold; 1) to assess the status of MSD in Uganda and understand farmers' preferences and varietal selection criteria for maize using a participatory rural appraisal (PRA), 2) to screen for MSD resistance in early generations of segregating maize populations using conventional method, 3) to screen for resistance to MSD using SSR marker assisted selection , 4) to compare the effectiveness of marker assisted selection and conventional methods for selection for resistance to MSD, and 5) to compare costs associated with MAS and conventional selection methods. Results of PRA showed that unreliable rainfall and insect pests were the dominant constraints to maize productivity in Uganda. Diseases were ranked fifth among the production constraints . Maize streak virus disease was considered the most important disease constraint. Farmers showed common preference for high yielding and early maturing cultivars. However, farmers had other special preferences which were diverse and included large, white and high test density kernels for marketing, and sweet taste, particularly for home consumption. Farmers' research priorities included tolerance to drought, resistance to insect pests and diseases, sweetness, prolificacy, resistance to lodging, and drooping leaves because theyt cover the soil fast and prevent weed growth. Conventional screening for resistance to MSD showed that backcross and selfing populations segregated in 1:1 and 3:1 Mendelian ratios confirming the presence of one major gene with simple inheritance . Severity and incidence of disease were positively correlated suggesting a non-reference by the insects. In the selfing populations, the presence of complete esistance against MSD was suggested because frequency distribution patterns were highly skewed in favour of resistance. There was a decrease in disease severities with selection from BC1F1 to BC2F1 and from F2 to F3 generations indicating that high response to selection was achieved. On the other hand, one marker, umc1917, consistently polymorphic and eo-dominant was selected and used in MAS protocol. Results showed that the observed outcomes fitted the expected ratio of 1:2:1 for a F2 population and 1:1 for a BC1F1 population (X2 not significant). Evaluation of F3 and BC2F1 progeny selected using markers showed low disease severity suggesting that marker assisted selection was effective. However, the study showed that the presence of the O'Tl, was not consistent with symptom expression in the field. Evaluation of lines in three-way crosses identified ten potential lines that were high yielding, highly resistant to MSD and stable across three locations. Both MAS and conventional selection were equally effective in identifying high yielding lines although resistance was higher under MAS. Costs of MAS and conventional method varied depending on the units for comparison. The total costs of conventional method were higher than that of MAS in both first and second selection cycles. Comparing costs per row for conventional and costs per plant or data point for MAS showed that conventional selection was 2.4 times more expensive than costs per sample for MAS. However, costs per plant for MAS were 6.6 times higher than for conventional selection. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006