A dissertation submitted in partial compliance with the requirements for the Masters Degree in technology: Homoeopathy, Technikon Natal, 1999. / The most common and difficult insect to control in the greenhouse is the whitefly. Sweetpotato whitefly (Bemisia tabaci Genn.) was the species of whitefly selected to be investigated in this trial. Sweetpotato whitefly is a major pest on a variety of plants, ranging from ornamental flowers to agricultural crops such as tomato and cotton, resulting in important financial losses. Effective control options of sweetpotato whitefly are limited. / M

The false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), is an important pest of citrus in South Africa and challenging to manage due to its inconspicuous nature. An effective method currently being employed for the area-wide suppression of the FCM is the Sterile Insect Technique (SIT) and the effective dispersal of sterile moths is very important for success with SIT. This study was conducted in the Addo area of the Sundays River Valley (Eastern Cape) where the programme is commercially used. In this study, sterile male moths were released in different orchards on a citrus farm, and in nearby veld at different times of the year, and their dispersal was monitored through the use of pheromone traps. Various climatic factors were monitored. This provided insight into the local dispersal of sterile male FCM adults in response to abiotic cues (particularly climatic factors). The movement of the FCM in four citrus cultivars, namely lemons, navel and Valencia oranges and mandarins and in the nearby veld (open field), was determined at six different stages of the year. Results clearly indicated that sterile FCM movement is concentrated within citrus orchards, as very few moths were trapped beyond 30 m from the release point, particularly in navel and Valencia orchards. Of the climatic factors measured, minimum and maximum temperatures had the most significant influence on FCM dispersal, and based on the results, various recommendations are made for the releases of sterile FCM in an area-wide SIT management programmes on citrus. A better understanding of the dispersal capabilities of the FCM in an agricultural system, under different conditions and at different times of the year, is invaluable not only in improving release strategies in an SIT programme but in planning future control strategies against the FCM.

Typescript. / Digitized by Kansas Correctional Industries

No description available.

Thesis (PhD(Agric) (Horticulture))--University of Stellenbosch, 2005. / Bitter pit fruit in commercial consignments of apples still poses an economic threat to exporters from South Africa. Bitter pit develops pre-harvest, but gets progressively worse during storage and is only traceable once the lesions appear after storage. Accurate, early indications of bitter pit incidence will allow for remedial pre-harvest measures in the field, e.g. Ca foliar applications, to reduce the potential losses. Similarly, the automatic detection of a bitter pit fruit during packing will reduce financial losses by identifying unacceptable fruit before shipping. Fluorescence imaging is a fast, non-destructive technique, able to evaluate numerous fruits individually. Results of pre-harvest imaging on apples to identify fruit susceptible to bitter pit showed that pitted fruit were correctly classified, but misclassification of non-pitted fruit with fluorescence imaging was still too high. NIR-spectroscopy point meter readings could distinguish visible bitter pit lesions from healthy tissue. Important wavelengths associated with visible bitter pit were identified. This technique could also identify immature apples, more prone to bitter pit development. It could however not distinguish between bitter pit and non-pitted fruit when applied randomly on the calyx end of apples at harvest. Pre-harvest foliar applications to increase fruit Ca content and reduce bitter pit incidence, is a standard practice world wide. External Ca uptake by fruit was monitored to determine the efficacy of applications during different stages of fruit development. Two periods of efficient uptake of external Ca were identified, viz., cell division and the last few weeks before harvest. Foliar Ca applications from 40 days after full bloom were more effective in increasing fruit Ca content and reducing bitter pit incidence than at 80 days after full bloom, which was recommended previously. Mineral analysis of fruit has been used with variable success to predict bitter pit prior to harvest. The possibility of increasing the accuracy of existing predictive models by using analysis of individual fruit rather than pooled samples, was investigated. By improving the normality of different mineral distributions and decreasing the overlap between pitted and non-pitted fruit classes, it was attempted to improve the reliability of predictions based on variable threshold values. The Ca distribution showed a variation between pitted and nonpitted classes, but still a significant overlap between classes reduced the accuracy of the predictive capacity of this distribution. Even though our results produced a correct classification of 85% for non-pitted fruit, which can be useful, this was still below the required tolerance, of less that 2%, expected on the market. The effect of pruning and fruit bearing position on two-year-old wood on dry mass and Ca allocation of fruit was determined. ‘Golden Delicious’ fruit set was the lowest at the basal bearing position compared to the other positions evaluated and was contrary to expectations. Fruit in a terminal bearing position was superior to the basal position regarding total dry weight and fruit size. Distal wood possibly inhibited growth and set on the basal position via auxin distribution. Ca allocation differed between seasons and cultivars and could either be influenced by bearing position or presence or absence of re-growth.

The within-field spatial distribution of F₁, F₂, and F₃ pink bollworm (PBW) (Pectinophora gossypiella Saunders) generations were modeled with Taylor's power law (TPL), Iwao's patchiness regression (IPR), and the geostatistical semivariogram. Kriging interpolation was used to grid data for the generation of isarithmic maps. Distributional patterns and movements within a field are displayed in a time series of three maps depicting density across the field. The sampling protocol was replicated in eight commercial cotton fields in south-central Arizona during 1985 and 1986. Permanent sample stations were situated throughout the fields on a regular grid pattern. Samples were collected during the peak larval population and handled so as to maintain the integrity of site-specific samples (spatially identified by X,Y coordinates). TPL and IPR could not be used satisfactorily to model the F₁ generation. TPL fit the observed F₂ and F₃ data better than IPR. Both methods predicted the F₂ to be more highly aggregated than the F₃. For a given precision, optimum sample size increased when TPL and IPR model parameters were incorporated into sample size formulae relative to a formula which assumed random distribution. Ninety-five percent of the modeled PBW distributions were autocorrelated in 2-dimensional space and shown to conform to regionalized variable theory by the successful application of geostatistics. The semivariogram models are in conceptual agreement with traditional models and represent a worthy alternative to traditional modeling methodology. The semivariogram models have a large nugget effect proportion (average = 67%) which, in combination with low PBW density in commercial fields, limits the applicability of geostatistics in this system. Isarithmic maps showed that F₁ larvae are either localized near a field edge or generally scattered throughout the field. No consistent inter-generational dispersal pattern was identified. The use of systematic grid sampling is most advantageous (relative to random sampling) when density and the spatial dependence of samples is high, or many samples can be taken. Systematic sampling and kriging estimation yielded more precise estimates than random sampling and classical statistics, but the advantage was buffered by low PBW densities and large nugget effect.

No description available.

No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016. / The entomopathogenic nematodes (EPNs) have emerged as an important group of insect pests. The EPNs which comprise the Steinernema genus share symbiotic associations with Xenorhabdus bacteria. This research project focused on isolating and characterizing a novel and indigenous EPN isolate with its associated bacteria. The biological control potential of the nematode was investigated in the areas of host infectivity, infective juvenile recovery and progeny yield. These processes were investigated at three different factors. These included time, population size and temperature. The infectious abilities of the symbiotic bacteria were also evaluated without the contributions of the nematode partner at different bacterial doses, time intervals and temperature regimens. The genome of the bacteria was thereafter acquired through whole-genome sequencing and annotation techniques to elucidate the virulence mechanisms and genes involved in temperature adaptation. The species isolated in this investigation was novel. The species shared an 85 % maximum identity to and taxonomically grouped with the species Steinernema khoisanae. The two species shared a common ancestor but the extended branch length of the species under investigation substantiated its novelty. The EPNs infected hosts at different time intervals, population densities and temperature regimens. However, the EPNs performed these processes to different extents. Host mortality significantly increased with time. The EPNs also infected insect hosts at the two experimental temperatures. However, host mortality was higher at the temperature regimen of 20° C and lower at 30° C. Host infections were not significantly different at two tested population densities of 500 and 1000 infective juveniles. The levels of interaction between temperature and time and temperature population density were not statistically significant. The subsequent biological process of recovery was evaluated. The EPNs recovered at both population densities and temperature regimens. The infective juvenile recoveries were statistically insignificant at both population densities and temperature regimens. Since recovery was based on the mere presence of progeny infective juveniles, the percentages were high which contributed to the statistical insignificant findings. This also contributed to the non-significant interaction between population density and temperature. The last biological process investigated was the progeny yield of infective juveniles. The yields were significantly different between both population densities of infective juveniles and temperature regimens. Higher yields were obtained at the temperature regimen of 20° C and 25° C. Lower yields were obtained at 30° C. The unexpected finding was higher progeny yields obtained from the lower population densities of infective juveniles. This contributed to the significant interaction present between population density and temperature. The bacteria were thereafter molecularly characterized. The symbiotic bacteria shared a 99 % sequence similarity to the species Xenorhabdus sp. strain GDc328. It was interesting to observe the infectious abilities of the bacteria without contributions from the EPNs. This study was measured at different bacterial doses, time intervals and temperature regimens. Host mortality was achieved without contributions from the EPN. Host mortality significantly increased with bacterial dose and time. Host mortality was also significantly different between each temperature regimen. Higher mortalities were observed at 30° C and lower mortalities were observed at 20° C. The differences in the performance between the EPN-bacterial partnership and the bacteria alone were attributed to the manner in which adaptation occurred. Since the EPN-bacteria existed as a bi-partite entity, the partners evolved as a bi-partite complex. The bacteria were removed from the symbiosis and cultured individually. External factors may have re-shaped the performance of the bacteria at the different temperature regimens. To further understand the genetic mechanisms of temperature adaptation, host infectivity and symbiosis, the draft whole genome sequence of the bacteria was then acquired. The genome of the bacteria comprised several genes which encoded the flagella system of the bacteria. Also pairs of co-localized toxin-antitoxin genes were discovered. Temperature acclimatization was performed through different cold and heat shock proteins and lastly several molecular chaperones. The studies showed that the species Steinernema spp. and its associated symbiotic bacteria Xenorhabdus sp. strain GDc328 were good bio-pesticide candidates for application against endemic insect pests. / LG2017

Naturalists, state administrators and farmers in France and its colonies developed a myriad set of techniques over the course of the long eighteenth century to manage the circulation of useful and harmful insects. The development of normative protocols for classifying, depicting and observing insects provided a set of common tools and techniques for identifying and tracking useful and harmful insects across great distances. Administrative techniques for containing the movement of harmful insects such as quarantine, grain processing and fumigation developed at the intersection of science and statecraft, through the collaborative efforts of diplomats, state administrators, naturalists and chemical practitioners. The introduction of insectivorous animals into French colonies besieged by harmful insects was envisioned as strategy for restoring providential balance within environments suffering from human-induced disequilibria. Naturalists, administrators, and agricultural improvers also collaborated in projects to maximize the production of useful substances secreted by insects, namely silk, dyes and medicines. A study of these scientific and administrative techniques will shed light on how scientists, administrators and lay practitioners in the French Enlightenment came to assess and manage the risks and opportunities afforded by the related processes of commercial and ecological globalization.