No. 5/2003

Anders Skonhoft
Nils Chr. Stenseth
Herwig Leirs
Harry P. Andreassen
Loth S.A. Mulungu

The paper treats the economy of controlling an African pest rodent, the multimammate rat, causing major damage in maize production. An ecological population model is presented and used as a basis for the economic analyses carried out at the village level using data from Tanzania. This model incorporates both density-dependent and density-independent (stochastic) factors. Rodents are controlled by applying poison, and the economic benefits depend on the income from maize production minus the costs for maize production, fertiliser and poison. We analyse how the net present value of maize production is affected by various rodent control strategies, by varying the duration and timing of rodenticide application. Our numerical results suggest that, in association with fertiliser, it is economically beneficial to control the rodent population. In general the most rewarding duration of controlling the rodent population is 3-4 months every year, and especially at the end of the dry season/beginning of rainy season. The paper demonstrates that changing from today's practice of symptomatic treatment when heavy rodent damage is noticed to a practice where the calendar is emphasised, may substantially improve the economic conditions for the maize producing
farmers. This main conclusion is quite robust and not much affected by changing prices and costs of the maize production.