Modelling the vertical distribution of insects

The Weibull distribution has been used to model the vertical distribution of insects under a number of activities: natural flight without any artificial stimulus, resting behaviour, and response to trapping involving colour attractants and odour baits. Initial approximations of the Weibull parameters are obtained using the least squares method, with more accurate values computed using the maximum likelihood estimates. Coefficients of determination are obtained after linearization of the Weibull equation and results show that these coefficients are generally high, indicating suitability of the model for fitting the observed data. The model yields an analytical formula for determining the mean heights at which the activities tend to occur. The model is tested on data from three sources: coleoptera in natural flight over Tallulah, Louisiana; Glossina palpalis palpalis at rest during the dry season in Nigeria; and catches of Glossina spp., in Rwanda, by traps placed at varying heights above the ground. Results show that different species of insects tend to fly, rest or be trapped at heights which are characteristic of the species.