Use of parametric and non-parametric survival analysis techniques to evaluate the effectiveness of two acaricides in controlling tsetse flies. (<i>Diptera Glossinidae</i>).

Abstract

This paper presents parametric and non-parametric survival analysis procedures that can be used to compare acaricides. The effectiveness of Delta Tick Pour On and Delta Tick Spray in knocking down tsetse flies were determined. The two formulations were supplied by Chemplex. The comparison was based on data collected from trials carried out in Zimbabwe at Rukomichi Research Station in 2003. Rukomichi Research Station is owned by the Department of Veterinary Services and is mainly used for conducting research on tsetse flies. The Kaplan Meier estimate of survivor and hazard function was used as the non-parametric procedure for comparing survival times of tsetse exposed to Delta Tick Spray and Delta Tick Pour On. In addition the log rank statistic was also used to explore the differences between the two formulations. The parametric procedure assumed that the survival times follow a lognormal distribution after checking the suitability of the distribution and estimating the hazard, survivor function and quartiles assuming the distribution. A proportional hazard model was also fitted to compare the two formulations. The non-parametric procedure revealed that the median survival times of tsetse exposed to Delta Tick Pour On was 10 minutes compared to 12 minutes for those exposed to Delta Tick Spray. The parametric procedure showed that the median survival time of tsetse exposed to Delta Tick Pour On was 10.59 minutes compared to 13.70 for those exposed to Delta Tick Spray. The proportional hazards model indicated that the hazard of being knocked down is 1.335 more for tsetse exposed to Delta Tick Pour On than those on Delta Tick Spray (p < 0.001). Keywords: Acaricides, parametric, non-parametric survival analysis procedures, tsetse flies