Investigating the simultaneous effect of age and temperature on the population dynamics of female tsetse flies

[摘要] ENGLISH ABSTRACT: Age and temperature are two factors that affect mortality in adult tsetse flies. Both are foundto be very important, but the simultaneous effect of these factors on the mortality rate havenot been studied. This study seeks to address this, with an application to a population offemale tsetse, using a model based on partial differential equations. Adult mortality is agedependentand is modelled as the sum of two exponentials, with four parameters (coefficientsof each exponential): numerical analysis of a population model with this mortality structurepredicts exponential growth. Analysis of each of the parameters through parameter variationshows that two of these parameters control the mortality of the nulliparous (ages 0 − 10days) flies only while the other two only take care of flies of mature ages. Measurement ofthe impact of these parameters on the mortality of tsetse of different ages by the normalizedforward sensitivity index method is also carried out. This is followed by fitting the modelbased on the age-dependent mortality along with a constant tsetse birth rate to data representingthe catches of female Glossina pallidipes at Rekomitjie Research station, Zimbabwe.Considering a three parameter adult tsetse mortality, parameter analysis shows the effect ofone of the parameters to affect the mortality of flies of all ages while a second controls only themature tsetse flies of reproductive ages. A further analysis resulted in the estimate of theseparameters as functions of temperature, thereby leading to the establishment of an age andtemperature-dependent adult tsetse mortality. Using data for the daily average temperaturerecords obtained in 1981 on Antelope Island, Lake Kariba, Zimbabwe, daily changes in thepupal duration (adult tsetse birth rate) changes negatively with temperature change. Incorporatingthis (temperature-dependent ) birth rate into the model, together with the establishedage and temperature-dependent adult mortality, the adult tsetse population dynamics is explorednumerically. The latter model is then fitted to population data of female Glossinamorsitans morsitans obtained from the same Island and for the same period as used forthe temperature data. The data suggests peak tsetse population to be in the month of Julyand lowest in the month of December. The first quarter of the year is predicted to be mostfavorable for breeding tsetse while the second, showed a period of stable growth rate and atime of tsetse abundance. In addition, the dynamics with both age and temperature showed anon-uniform daily population growth contrary to that with age effect only. This study has enhancedour understanding of tsetse population dynamics for age and temperature-dependentadult mortality with temperature-dependent pupal duration and suggests the period of tsetseabundance on Antelope Island.

[发布机构] Stellenbosch University