Alternative Specifications and Extensions of the Economic Threshold Concept and the Control of Livestock Pests

Outlines economic threshold models developed by various authors as an aid to decision-making about pest management. Particular attention is given to the models proposed by Stern et al. (1959) and by Headley (1972) and the major differences in their concepts of the economic threshold. Limitations and scope for applying these models is discussed as well as differences in the extent of their applications are reviewed. After considering general issues in this respect, particular matters are given attention such as difficulties raised by 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. An extension is provided for multiple species pest models to incorporate both multiple-pest species and pest resistance. The presence of fixed costs and the complexities in determining actual cost functions for pest control are also raised as additional qualifications to existing economic models of decision-making about pest control. The combination of these factors limits the applicability of profit-maximising thresholds for livestock management, especially compared to other strategies such as prophylaxis, although improvements in dynamic biological modelling and computer simulations are increasing the scope for applying profit-maximising models.