This paper considers the dynamics of a two-dimensional discrete-time model for host-parasitold interactions, and shows that the model has two attractors: the fixed point where two species coexist and a boundary cycle where the parasitoid is absent. The analysis with the Liapunov exponent confirms that this kind of bistability is common in this model. The generality of this phenomenon in host-parasitoid interactions is also discussed. (c) 2005 Elsevier Inc. All rights reserved.