Masters Degrees (Agricultural Economics)

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Browsing Masters Degrees (Agricultural Economics) by browse.metadata.advisor "Giliomee, J. H."

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    A study of the biology and control of the western flower thrips, Frankliniella occidentalis Pergande
    (Stellenbosch : Stellenbosch University, 1996) Badenhorst, Jacqueline Anne; Giliomee, J. H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agricultural Economics.
    ENGLISH ABSTRACT: The effect of temperature on the development of Frankliniella occidentalis, Pergande on lima bean (Phaseolus limensis) leaf discs was investigated at five constant temperatures (15°, 18°, 22°, 25° and 30°C). Further studies examined the effect of temperature on reproduction and population growth at three constant temperatures (18°, 25° and 30°C). Life table studies showed that adult longevity and developmental rate of each life stage were inversely related to temperature. The prepetual and pupal stages showed greatest sensitivity to temperature. The nett replacement rate (R,) was highest at 25°C and th intrinsic rate of natural increase (r,) highest at 30°C. The generation time (T) declined with an increase in temperature. Fecundity of females peaked at 25°C. The minimum threshold for development was found to be 8.9°C and degree days for development ranged from 198.9 to 232.9. Populations of male and female F. occidentalis were monitored over an 18 month perdiod in a chrysanthemum glasshouse. Fluctuations in numbers female were significantly correlated to temperatures both within and outside the glasshouse, while male numbers showed no correlation at any time. Males outnumbered females at low population densities. When high numbers of thrips were caught, females formed more than 65% of the trapped individuals. The susceptibility of two strains F. occidentalis to endosulfan and formetanate was tested in residue on-glass bioassays in the laboratory. Diagnostic doses resulting in approximately 50 % and 90% mortality are proposed for endosulfan, namely 280 and 840 ppm a.i., respectively. Similarly diagnostic doses of 6 and 75 ppm a.i. are proposed for formetanate.