Fitness Consequences of Hibernal Diapause in the Pitcher-Plant Mosquito,wyeomyia Smithii

The mosquito, Wyeomyia smithii, develops only within the water-filled leaves of the purple pitcher plant, Sarracenia purpurea, where it overwinters in larval diapause. We reared uniform-aged cohorts in the leaves of intact plants in three environments: near-optimal summer conditions, intentionally stressful summer conditions, and a 23-wk simulated winter. Overwintering W. smithii suffered a 60% loss in fitness (R0), comparable to the 68% loss in fitness imposed by the summer stress. Overwintering cohorts lost fitness through reduced survivorship, fecundity, fertility, adult longevity, and mass-specific fecundity. We argue that very real trade-offs occur between summer performance and winter performance among temperate insects in general. Survivorship and reproduction of the overwintering generation should therefore be an important source of selection shaping not only the seasonal expression of dormancy, but also the evolution of summer life-history syndromes as well.