Univoltine and bivoltine life cycles in insects: A model with density-dependent selection

Selection for univoltine and bivoltine life cycles in insects under resource-limited but favourable temperature conditions is analyzed with a difference equation model including density-dependent population dynamics based on the conceptual framework of an evolutionarily stable strategy. The model predicts that the bivoltine type can spread in a univoltine population when the fraction of density-independent rate of annual increase by producing a second generation exceeds the survival rate during diapause of the univoltine type, but monopoly of the bivoltine type is not possible unless it attains an equilibrium population density exceeding that of the univoltine type. The applicability of the model prediction in explaining the occurrence of a partial bivoltine cycle in predominantly univoltine population in the temperate zones is discussed.