The excitation of instabilities caused by the parametric coupling between an external source and the normal modes of bubbly flow is investigated. It is shown that the presence of two species of bubbles gives rise to two types of parametric excitations. In the first one the frequency of the external source is smaller than the larger of the natural frequencies of the species. As a result, the excited mode is nonoscillatory. In the second type the driving frequency is bigger than both natural frequencies and the resulting instability is oscillatory. The threshold amplitude of the external source is calculated as well as the growth rates and frequencies of the different types of instabilities.