Parasitoid sex allocation affects co-evolution of patch selection and stability in host–parasitoid systems

Previously, we have show that the co-evolution of patch selection strategies of hosts and parasitoids in heterogeneous environments can lead to contrary habitat choices in which the hosts preferentially select patches that the parasitoids avoid. Since this work did not include the variable parasitoid sex ratios that have been found in field and laboratory systems with contrary choices, we extend previous analyses to determine how parasitoid sex allocation co-evolves with host and parasitoid patch preferences. In our analysis, we assume the environment consists of two patch types: lower quality patches and higher quality patches. In the lower quality patches, hosts have a lower intrinsic rate of growth and female parasitoid larvae are less likely to survive than male parasitoid larvae. Our co-evolutionary analysis reveals that the co-evolved parasitoids preferentially search for hosts in higher quality patches, lay primarily female eggs on hosts encountered in these patches, and are more likely to lay male eggs on hosts encountered in the lower quality patches. As a co-evolutionary response, the hosts lay twice as many eggs in the poorer patches as they would if parasitoid sex ratios did not evolve. We conclude by showing that the co-evolution of parasitoid sex allocation with patch selection can stabilize host–parasitoid interactions even when co-evolution of patch selection by itself does not.