Jointed cactus, 0puntia aurantiaca Lindley, remains a problem and continues to expand its range in South Africa, in spite of a mandatory herbicidal control. programme. The feasibility of biologically controlling the weed is being explored because the cost of herbicides has escalated and, if it succeeds, biological control is permanent self perpetuating and relatively cheap. This thesis describes the introduction and release in South Africa of the phycitid moth, Tucumania tapiacola Dyar, as a potential biocontrol agent against jointed cactus. A preliminary objective of the study was to resolve the taxonomic confusion within the genus Tucumania, so that the various populations of the moth from widespread localities and from different host plants could be identified. The efficiency of mass-producing T. tapiacola in the insectary was continually improved through investigations of the insects biology, and its response to various environmental parameters. Techniques were developed to manipulate the different life-stages of T. tapiacola so that every release was made with the maximum possible number of individuals, all in the same stage of development. Trials were made with various methods for transporting and releasing T. tapiacola in the field, and the most successful of these were employed during the establishment programme. In all, approximately 830 000 T. tapiacola eggs, larvae and adults have been released at seven localities in South Africa, between May 1977 and February 1982. So far, the moth has failed to establish for more than three to five generations at any release site, for reasons that were not immediately apparent. The mortality factors acting against the immature stages of T. tapiacola have been investigated and quantified. The accumulated data were used to construct partial-life-tables and survivorship curves. These show that survival of the eggs, larvae and pupae differed in shaded and exposed habitats, and on small, medium and large O. aurantiaca plants. The overall mortality suffered by the immature stages alone did not account for the establishment failure. Alternatively, genetic problems that are commonly associated with the collection, mass production and release of biocontrol agents may have been responsible for the failure. Methods of overcoming these problems during future releases are discussed.

Inbreeding was thought to be responsible for the loss in the second filial generation (F₂) of Amalafrida leithella Dyar, Cactoblastis mundelli Heinrich, Nanaia sp. Heinrich, Sigelgaita sp. Heinrich and Sigelgaita transilis Heinrich in the laboratory. This pre-empted the investigation of the effects of inbreeding on another cactophagous moth, Mimorista pulchellalis Dyar, an established biological control agent of jointed cactus in South Africa. Initially three populations were set up. A randomly-mating control (OUT 1) population, and a sibmating experimental (IN 1) population, consisted of laboratory-reared stock . A second experimental population (KR 1) comprised a small number of field-collected randomly-mating individuals which recreated the conditions under which the five abovementioned species were lost. The inbreeding depression of fifteen fitness components was assessed. The mean values of each component in each generation of treatments IN 1 and KR 1 were compared with those of OUT 1. In addition the mean values of IN 1 were regressed against the coefficients of inbreeding since inbreeding depression is linear with respect to the probability of two genes at any locus being homozygous through ancestry. The component egg viability was important because a reduction in OUT 1, IN 1 and KR 1 in the F₂ resulted from mated females producing no viable eggs. Duplicate treatments OUT 2, IN 2 and KR 2 were set up to confirm whether this was a general F₂ phenomenon. Assessment of the fitness components prevented a direct evaluation of the numbers of offspring produced. However a hypothetical estimate of population size and growth rate was made using the percentage survival calculated from life-table analysis. Although not statistically demonstrable in the component analysis, life table analysis indicated that egg viability suffered an inbreeding depression and affected population fitness. It was also evident that treatments OUT 1 and 2 were fitter than treatments IN 1 and 2 and KR 1 and 2 with respect to population fitness. Thus, inbreeding, resulting from sibmating and introduction of a small number of individuals to a laboratorYJ caused a decrease in numbers of offspring produced and population growth rate. This is important in relation to the demise of the cactophagous Lepidoptera and to future biological control programmes.

The cochineal insect Dactylopius austrinus De Lotto, which was released on jointed cactus, Opuntia aurantiaca Lindley, in South Africa in 1932, failed to bring the weed under an acceptable level of control in spite of the encouraging results during the first few years after release. The reasons for this apparent failure were never clearly understood. In 1957 the State embarked on an intensive herbicidal control programme which is still in force today. This sustained and expensive programme has undoubtedly reduced the density of the weed in most areas but has failed to solve the problem and the plant continues to expand its range. The biological control of o. aurantiaca in South Africa has been fundamentally influenced by this chemical control campaign. The relationship between chemical and biological control methods is reported in this study.

From the introduction: The work on Mimorista is divided into two sections: a laboratory orientated study which describes the biology and rearing techniques and a field orientated study where the establishment of the insect and its impact on jointed cactus populations are examined. In the final chapters the integration of this insect in the current control program are discussed and recommendations regarding its future in South Africa are given.

The successful biological control of the shrub-like prickly pear Opuntia stricta Haworth in Australia by cactoblastis cactorum (Berg) was not repeated when C. cactorum, derived from the Australian population, was released in South Africa in the 1930's against the tree prickly pear Opuntia ficus-indica (L.) Miller. Resistance of the woody portions of o. ficus-indica to attack by C. cactorum was regarded as the main reason for the poor performance of C. cactorum in South Africa. C. cactorum also oviposits and feeds on Opuntia aurantiaca Lindley, which is currently South Africa's most important weed and which is also considered to be partly resistant to attack by C. cactorum. This study had three main objectives: (i) to compare the ecology and effectiveness of C. cactorum as a biological control agent on O. ficusindica and O. aurantiaca; (ii) to reassess why C. cactorum has not been as effective a biological control agent in South Africa as it has been in Australia; and (iii) to evaluate whether inundative release or the importation of new biotypes of C. cactorum from South America (where it is indigenous) might be feasible methods of improving its effectiveness as a biological control agent of O. aurantiaca in South Africa. All field work was undertaken at a site near Grahamstown in South Africa. The ecology and effectiveness of C. cactorum on O. ficus-indica and O. aurantiaca was assessed in terms of its oviposition behaviour, survival and feeding on these host plants. The proportion of C. cactorum eggs laid on O. ficus-indica and O. aurantiaca was similar and was influenced by the size, conspicuousness and condition of the host plant as well as by the proximity of the host plant to moth emergence sites. Factors affecting oviposition site selection on the plant are also considered. Life tables, compiled for a summer and a winter generation, showed that the survival of C. cactorum was greater on O. ficus-indica than on O. aurantiaca, mainly because higher egg predation by ants occurred on the latter host plant species. During the period of study, the population size of C. cactorum was reduced by a number of mortality factors, of which egg predation and the effects of low temperatures on fecundity were the most important. Although there was evidence of a partial, positive response by predatory ants to C. cactorum egg densities on plants, the extent of egg predation was also affected by other factors, particularly seasonal effects. C. cactorum destroyed a greater percentage of cladodes on O. ficu-indica than on O. aurantiaca, but even on O. ficus-indica it was unable to contain the growth of plants within the study area. C. cactorum larvae rarely killed the woody rooted cladodes of O. ficus-indica and O. aurantiaca and consequently whole plants were not often destroyed. The detrimental effects of host plant resistance, natural enemies and climate on the effectiveness of C. cactorum as a biological control agent all appear to be greater in South Africa than in most of the regions occupied by C. cactorum in Australia. A field experiment conducted at the study site showed that inundative release methods for improving the effectiveness of C. cactorum on O. aurantiaca are not feasible. The importation of biotypes of C. cactorum from South America that might be better suited for destroying O. aurantiaca infestations in South Africa, is also not a viable option. Results of a survey of a 218 ha area that is regarded as being heavily infested with O. aurantiaca, illustrate how this cactus species has been overrated as a weed problem. It is argued that the present strategy for O. aurantiaca control in South Africa is not based on sound economic or ecological criteria.

In this paper we study packet delay and loss rate at the University of Fort Hare network. The focus of this paper is to evaluate the information derived from a multipoint measurement of, University of Fort Hare network which will be collected for a duration of three Months during June 2011 to August 2011 at the TSC uplink and Ethernet hubs outside and inside relative to the Internet firewall host. The specific value of this data set lies in the end to end instrumentation of all devices operating at the packet level, combined with the duration of observation. We will provide measures for the normal day−to−day operation of the University of fort hare network both at off-peak and during peak hours. We expect to show the impact of delay and loss rate at the University of Fort Hare network. The data set will include a number of areas, where service quality (delay and packet loss) is extreme, moderate, good and we will examine the causes and impacts on network users.