Masters Degrees (Zoology and Entomology)
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Browsing Masters Degrees (Zoology and Entomology) by Author "Brown, Deodanda"
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Item Open Access Aspekte van die bio-ekologie van Aedes aegypti (Diptera: Culicidae)(University of the Free State, 2001-07) Brown, Deodanda; Van der Linde, T. C. de K.English: Aedes aegypti (Linnaeus) was reported for the first time in 1996 in the Bloemfonteinregion. Due to the fact that this was not the normal distribution area of this species, the main objective of the study was to do research on the bio-ecology of Ae. aegypti in order to determine whether it can get established in the Free State. Trapping of both adult and immature mosquitoes were done at two weekly intervals from 1996 - 1998. This was done at three localities in the Bloemfontein urban area viz the "Dam van Trane", Valley of Seven Dams and the Pony Club Dam, in the region where this species was recorded for the first time. The aim of these trappings was to get a general idea of the species diversity, relative abundance and seasonal fluctuations of the mosquitoes in this area. Ten mosquito species were collected during the study. Aedes juppi McIntosh was the most abundant species, accounting for 36,6% of the total catch followed by Culex theileri Theobald (32,4%) and Aedes aegypti which constituted only 0,5% of the total catch. The seasonal fluctuation and abundance of all the species that were caught, were analyzed and correlated with meteorological parameters such as temperature, rainfall and relative humidity. From these is was concluded that no parameter can be singled out, but that a combination of all the above parameters playa role in the occurrence and distribution of the mosquito species.An Ae. aegypti laboratory colony was established. Results originating from various experiments contributed to the sucessful colonization of this species. Adults were kept in electronically controlled rearing rooms at a temperature of 25°C ± 1°C and a relative humidity of70% ± 2%, with a day-night cycle of 12 hours light and 12 hours darkness including a dawn and a dusk period of one hour respectively. For carbohydrate feeding, adults were fed on 7% sugar water and pigeons were used for bloodmeals. Oviposition occurred on white strips of paper towel which were placed in black plastic containers filled with 300ml of 0,02M NaCl-solution and a small amount of larval food. These containers were placed inside the mosquito cages and left for three days.Eggs had to be dried for at least four days at 25°C and a relative humidity of >68% before they were submerged in the water for hatching to occur successfully. Larvae were held in shallow pans filled with O,02M NaCI-solution and kept in the rearing rooms at 25°C_ They were fed a mixture of brewer's yeast and an infant cereal. Carbohydrates play an important role in the bloodfeeding, ovipositioning and survival of the females. Females that were fed on cane sugar as carbohydrate source, performed significantly better in taking a bloodmeal and producing eggs than females that fed only on fruit. The fruit-fed females also had a significantly lower survival. If Ae. aegypti females have regular access to bloodmeals, they are capable of surviving on protein from the blood. Ae. aegypti larvae are able to take up NaCI from diluted solutions (O,OIM - O,02M) and are able to survive and develop in distilled water. NaCl-solutions above O,08M had a negative impact on larval development and at concentrations above O,12M NaCl survival is negatively influenced Successful development and survival of the immature stages occurred at temperatures between 15°C and 35°C. The optimum development temperature was 30°C. A constant temperature of 35°C however, had a negative influence on the physical size of the adults. The results obtained from the laboratory studies were used in an attempt to explain the occurrence of Ae. aegypti in the Free State and to try and determine whether this species will be able to establish itself permanently in the Free State.