Models for the rates of pupal development, fat consumption and mortality in tsetse (Glossinaspp)

Abstract

Environmental temperature is an important driver of the population dynamics of tsetse (Glossina spp) because the fly's immature stages are particularly vulnerable to temperatures (T) outside the range T = 16–32°C. Laboratory experiments carried out 50 years ago provide extensive measures of temperature-dependent rates of development, fat consumption and mortality in tsetse pupae. We improve on the models originally fitted to these data, providing better parameter estimates for use in population modelling. A composite function accurately models rates of pupal development for T = 8–32°C. Pupal duration can be estimated by summing the temperature-dependent daily percentage of development completed. Fat consumption is modelled as a logistic function of temperature; the total fat consumed during pupal development takes a minimum for T ≈ 25°C. Pupae experiencing constant temperatures <16°C exhaust their fat reserves before they complete development. At high temperatures, direct effects kill the pupae before fat stores are exhausted. The relationship between pupal mortality and temperature is well described by the sum of two exponential functions. Summing daily mortality rates over the whole pupal period does not reliably predict overall mortality. Mortality is more strongly correlated with the mean temperature experienced over pupal life or, for T ≤ 30°C, the fat consumption during this period. The new results will be particularly useful in the construction of various models for tsetse population dynamics, and will have particular relevance for agent-based models where the lives of individual tsetse are simulated using a daily time step.

Projecting the Potential Distribution of Glossina morsitans (Diptera: Glossinidae) under Climate Change Using the MaxEnt Model

“…Climatic variables may influence the transmission cycle of trypanosomiasis [ 8 ]; for example, temperature drives both relative abundance of and trypanosome infections due to tsetse flies. Specifically, temperature can influence the survival and growth rate of tsetse flies [ 9 ] as well as the growth and proliferation of trypanosomes within the tsetse flies. G. morsitans are diurnal and are only active between the temperatures of 18–32 °C [ 10 ].…”

Dispersal in heterogeneous environments drives population dynamics and control of tsetse flies

“…In terms of model parametrization, recent field and laboratory data on mortality, development and dispersal were incorporated into our model, decreasing the paucity of information on tsetse species other than G. m. morsitans [60]. Our sensitivity analysis highlights the need for more biological studies to better infer mortality variation with temperature, and more accurately estimate temperatures as perceived by insects, an issue recently raised for another tsetse species [60]. Such a complementary interplay between models, field observations and laboratory experiments is fundamental to make accurate predictions.…”

Extinction probabilities as a function of temperature for populations of tsetse (Glossina spp.)

“…Various workers have obtained mathematical expressions for the temperature dependence of such functions as daily survival probabilities for young, and mature, adult females, and pupae, and the inter-larval period and pupal duration [6,8,[14][15][16][17]. Using these functions allows us to estimate extinction probabilities, time to extinction and mean of tsetse population size at different levels of fixed temperatures.…”

“…The relationship between temperature and the instantaneous daily mortality rate of pupae is modelled as a the sum of two exponentials (Fig 1) [14].…”