A GENERIC POPULATION-MODEL FOR THE AFRICAN TICK RHIPICEPHALUS-APPENDICULATUS

We present a simulation population model for the African tick Rhipicep halus appendiculatus, based on previous analyses of the mortality fact ors most closely correlated with observed population changes at 11 sit es in equatorial and South Africa. The model incorporates temperature- dependent rates of egg production and development, climate-driven dens ity-independent mortality rates, particularly during the adult-larval stage, and density-dependent regulation of both nymphs and adults. Dia pause is also included for tick populations in southern Africa. The mo del successfully describes both the seasonality and annual range of va riation in numbers of each tick stage observed at each of 4 test sites in Uganda, Burundi and South Africa. Sensitivity analysis showed that the final version of the model is robust to 4-fold variation in most parameter values (that were per force based on informed guesses), but is more sensitive to the regression coefficients determining density-d ependent interstadial mortality (that were derived from analysis of fi eld data). The model is able to predict the seasonality of ticks from a site in Kenya where a full prior population analysis was not possibl e because only adults and nymphs had been counted. The model is potent ially applicable to other species of ticks, both tropical and temperat e, to predict tick abundance and seasonality as risk factors for tick- borne diseases.