The Simbad model has been developed by the authors for modelling the demography and feeding behaviour of the four main African species of cotton bollworms. Linked with the cotton crop simulation model Cotons®, CotonSimbad allows an assessment of yield loss due to a bollworm attack, given the size of the pest population, the species composition of the population, the date of the attack and the crop management sequence. The goal of the integrated model is to define rules allowing decision on a chemical spray according to the environment and the crop management. These decision rules have then to be tested at the on-farm level. This paper illustrates the use of CotonSimbad model to produce simple decision rules that can be tested in the field.