We introduce a multitype interacting particle system, which is a natural generalization of the contact process. Here, individuals in the population have two life stages, young and adult. Only adults can give birth and each new offspring is young. Transition from young to adult occurs at constant rate, and individuals die at rates that depend on their life stage. Important to the analysis of this process is the construction of a multitype dual process.
"The two-stage contact process." Ann. Appl. Probab. 9 (2) 331 - 351, May 1999. https://doi.org/10.1214/aoap/1029962745