Alternative specifications and extensions of the economic threshold concept and the control of livestock pests

This paper outlines economic threshold models developed by various authors as an aid to decision-making about pest management and their applicability to pests of livestock. The definitional confusions relating to economic threshold models are raised as are limitations for applying threshold models. Complexities in the nature of yield loss function due to uncertainty in pest densities, the presence of multiple pests, and the occurrence of pesticide resistance are discussed. An extension is provided that incorporates both multiple-pest species and pest resistance to control measures. Complications relating to the cost functions for pest control are considered. The combination of these factors limits the applicability of profit-maximising thresholds for livestock management, especially compared to other strategies such as prophylaxis.