The population biology of the free-living phase ofHaemonchus contortus

Abstract

A deterministic model for the demography of the free-living stages ofHaemonchus contortusis described. The model consists of three compartments: the pre-infective stages, comprising the eggs and first- and second-stage larvae combined; third-stage larvae in the faeces; and third-stage larvae on the pasture. The mortality(μj)of each of these stages was a function of temperature (K, where K = (degrees Celsius + 30)/100) of the form,μj= ajexp [xjK] + bjexp [– βjK]. The minimum time to second moult (γ) and the moulting rate thereafter (σ) were also functions of temperature (In [1/γ] = c1+ c2[1/K], and σ =d1exp[d2K] respectively). The rate at which L3 larvae migrated out of the faeces was treated as a constant (0.165/larva/day).