Complex periodic and aperiodic behaviours are reported in an unstirred Belousov-Zhabotinsky oscillatory reaction performed at temperatures varying between 0 degreesC and 8 degreesC. A route to chaos following a Ruelle-Takens-Newhouse (RTN) scenario is identified. Thus, temperature effects on the coupling between chemical kinetics, diffusion and convection, seem to be responsible for the observed RTN scenario. In this Letter we demonstrate that the temperature is a bifurcation parameter for the sequence period-1 --> quasiperiodicity --> chaos.