1,721,014 research outputs found
The phenomenon of Apis mellifera capensis laying workers in Apis mellifera scutellata colonies in the summer rainfall region of South Africa
Get PDFDissertation (MSc (Zoology and Entomology))--University of Pretoria, 2007.African honeybee workers, Apis mellifera scutellata can activate their ovaries under queenless conditions to produce male (haploid) offspring. In contrast, laying workers of the Cape honeybee, Apis mellifera capensis, produce female (diploid) offspring via thelytokous parthenogenesis. In the early 1990’s colonies of A. m. capensis were transported into the distribution area of A. m. scutellata (corresponding to the summer rainfall region of South Africa), leading to the “capensis calamity”. Laying workers of A. m. capensis invaded and killed colonies of A. m. scutellata leading to losses of thousands of commercial colonies. A survey of the apiaries in the A. m. scutellata region was conducted over 18 months from 1997 to 1998, to determine the extent of the problem. It was found that the parasites were established in many apiaries throughout the distribution range of A. m. scutellata. As the problem seemed to be more severe with commercial and migratory beekeepers, the apiaries surveyed were divided into risk groups related to beekeeping practices. The low risk group included apiaries of beekeepers in areas that are separated from commercial beekeepers and their high risk activities. These low risk colonies were sedentary vs the migration to high risk ares eg. Aloes, sunflower pollination areas, citrus and other fruit pollination areas of the high risk apairies. The apiaries were monitored and records of the colonies’ condition were taken. Samples of workers were collected for dissection. It was found that the low risk group had a lower rate of infection, a higher production of brood and honey and a higher rate of survival over a 12 month period. The significant characteristics for identifying infection of a colony were determined as being the colour of the workers, the brood pattern, the presence of multiple eggs in cells and the presence of the queen. Indeed, the presence of dark workers with a black scutellum, an irregular brood pattern, the presence of multiple eggs in cells and the absence of queen were all prevalent in infected colonies. As sample of workers from all inspected colonies were dissected and the average ovariole counts as well of the development stage of the ovaries proved to be significant variables in the diagnosis. Other variables eg. Ovariole counts, spermatheca size and aggression proved to be not significant, but in conjunction with other variables, could be used for diagnosis. The genetic nature of the invasive parasitic population was determined using polymerase chain reaction (PCR) analysis. Nine loci were tested and the DNA fingerprints of all individuals sampled throughout the summer rainfall region were proved to be identical. This genetic identity led to the descripter of these individuals as a pseudoclone. In contrast, workers of A. m. scutellata were tested with the same loci and showed the normal distribution of an out-breeding population. In order to investigate the spread of the parasite within an apiary, colonies were exposed to heavily infected hives and inspected regularly. Ninety five percent of the colonies had either died or absconded within 12 months. It is concluded that this phenomenon of social parasitism is the consequence of apicaultural activities and that it can be managed by adopting low risk beekeeping practices.Zoology and Entomologyunrestricte
Intracolonial demography, biomass and food consumption of Macrotermes natalensis (Haviland) (Isoptera: Termitidae) colonies in the northern Kruger National Park, South Africa
Get PDFDissertation (PhD)--University of Pretoria, 2003.This thesis reports on the number of individuals in Macrotermes natalensis (Hav.) colonies, their biomass and food consumption in the northern Kruger National Park (KNP). The ecology of M. natalensis is largely undocumented despite the abundance of colonies in southern African savannas. New approaches to mound excavation, sub-sampling and data management are introduced. Via the intracolonial demography of colonies the contribution of each caste in number or proportion is determined. Using this information in combination with body mass and mound density data, biomass per unit area has been computed indicating the importance of this termite in synecology. The measurement of food consumption gives further insight as to how much litter is removed, fragmented and redistributed as nutrients in the ecosystem. Mounds were completely excavated, termites collected by means of vacuuming, and colony size estimated by sub-sampling. It was estimated that, on average, small mounds contain more than 5 000, medium mounds more than 45 000, and large mounds more than 200 000 individual termites. A highly significant relationship between total number of individuals (N ) and mound height (h ) was found, given by lnN = 7.893 + 1.093h (r = 0.92). The proportion of soldiers was found to change as colonies grew larger. In order to derive biomass estimates, a statistical bootstrap procedure was carried out using three databases: body mass, colony population sizes and mound density. Live biomass for small, medium and large mounds was found to be 0.17, 1.40 and 4.16 kg. Dry/wet body mass ratios were established for workers (23.7 %), major soldiers (20.3 %), minor soldiers (35.3 %), nymphs (17.1 %), king (35.4 %) and queen (20.8 %). Average live and dry biomass was calculated to be 0.51 kg/ha (0.051 g/m2) and 0.11 kg/ha (0.011 g/m2). Geology, geomorphology, elevation, local relief, soil patterns and annual rainfall were the abiotic factors shown to be most influential in determining termite biomass, either directly or indirectly. Termite biomass is high in undulating areas where the elevation is 250-400 m, where granitic and rhyolitic soils occur, and where annual rainfall is high (650-700 mm) in the context of the region. Major workers fetch woody litter outside the nest through ingestion into the section of the crop and gizzard. Gut contents were dried, weighed, ashed and reweighed. The ash mainly represents soil particles. The ash-free mass of food that is consumed during a single foraging trip by a foraging individual is 0.166 ± 0.009 mg (CI). Frequency of foraging trips between the mound and food source was observed using translucent tubing. The annual food consumption is given by the formula 365mnp/t , where m = individual mass of ashed crop-gizzard contents, n = number of foraging major workers, p = daily foraging period, and t = individual time spent between nest and food source. Food consumption of this termite in the northern KNP is calculated to be 20.2 kg/ha/yr. It is shown that termites are primary decomposers and contribute to litter fragmentation and the recycling of nutrients into the soil. This thesis gives greater insight into aspects such as colony development, biomass investment and resource utilization of M. natalensis in the northern KNP.Zoology and Entomologyunrestricte
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Analysis of Varroa destructor infestation of southern African honeybee populations
Get PDFDissertation (MSc (Entomology))--University of Pretoria, 2007.The discovery of the honeybee-specific ectoparasitic mite Varroa destructor in South Africa in October 1997 raised the spectre of massive honeybee colony losses as has occurred in most parts of the world where the varroa mite has been found. This was particularly concerning in Africa because of the importance of honeybees in the pollination of indigenous and commercial crops, and because of the numbers of small-scale beekeepers in Africa. The mite has now spread throughout South Africa and is found in almost all honeybee populations, both commercial and wild, and is also now present in most neighbouring countries. Varroa has not left a trail of destruction in South Africa as had been expected and no large scale collapse of the honeybee population occurred, despite the majority of beekeepers deciding not to protect their hives with chemical varroacides. Some colony losses did occur at the front of the varroa spread, and all colonies were found to be deleteriously affected by the mite which developed populations of 50 000 and more in some colonies. Infected colonies were also not as efficient as pollinators as uninfected colonies. Colonies exhibited all the same varroa effects witnessed in other parts of the world, with the exception that the majority of colonies did not die as a result of the infestation. The relative tolerance of African bees to the varroa mite has been confirmed by the long-term monitoring of both wild honeybee populations and commercial stock, and by population dynamic studies of the mites. In both wild and managed honeybee populations varroa appears to have been reduced to the status of an incidental pest. The development of mite tolerance took 3-5 years in the Cape honeybee (Apis mellifera capensis) and 6-7 years in the Savanna honeybee (Apis mellifera scutellata). The rapid development of mite tolerance in the Cape bee is thought to be due to the well developed removal of varroa-infested brood and the short post-capping period of worker brood. Together these resulted in a very rapid increase in infertile mites in the colony, the collapse of the mite population, and varroa tolerance. Tolerance does not develop as rapidly in Savanna honeybees as the post-capping period in these bees is similar to that of European bees and does not result in as many infertile mites. Nonetheless, varroa tolerance in Savanna bees develops more rapidly than would be the case in European bees because of more effective hygienic removal of varroa-infested brood. In both Cape and Savanna bees, the absence of varroacide applications and a “live-and-let-die” approach to the wild and commercial honeybee populations was crucial to the developed of population-wide varroa tolerance, in contrast to the selective breeding and pesticide treadmill practised in most parts of the world in an effort to get rid of the varroa mite. Varroa destructor is concluded not to be a serious threat to honeybees and beekeeping in Africa, and efforts should be made to prevent the use of pesticides and techniques that could hinder the development of natural mite tolerance in Africa.Zoology and Entomologyunrestricte
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Senario SA letsatsi la tahlego le pheletso ya go ata ga nose ya mamapo ya Afrika
Get PDFInvitation to the first lecture of the UP expert lecture series delivered by Prof Robin Crewe, 26 August 2010 17:00, Senate Hall, Hatfield Campus, University of Pretoria.The threat to honeybee populations in the USA, Europe and Latin America over the past few years has received extensive media
attention.Yet, very little is said about African honeybee populations, even though honeybees come from Africa.Die bedreigde heuningbybevolkings in die VSA, Europa en Latyns-Amerika het die afgelope paar jaar baie aandag van die media
ontvang. Tog word daar baie min oor Afrika-heuningbybevolkings berig, alhoewel heuningbye vanaf Afrika kom.Tshosetso ya go ata ga nose ya mamapo ya USA, Yuropa le Amerika ya Lathine mo mengwageng e se mekae ya go feta e
hweditse tlhokomelo ye kgolo ya mediya. Le ge go le bjalo, ga go bolelwe kudu ka go ata ga nose ya mamapo ya Afrika, le ge e le
gore dinose di tswa Afrika
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