The Phenology of Pieris Napi Microstriata (Lepidoptera: Pieridae) During and After the 1975–77 California Drought, and its Evolutionary Significance

Interest in the theoretical basis of insect phenology has increased very markedly in recent years (Bradshaw, 1974; Cohen, 1970; Giesel, 1976; Levins, 1969). The evolution of phenological "strategies" via natural selection is of interest to ecologists and applied entomologists alike. Insect phenology involves responses to both "normal" and "abnormal" weather. The developmental plasticity displayed by a population may determine its survival in seasons of unusual meteorological stress and in turn may reflect a history of selection by recurrent exposure to that stress. The 1975-77 California drought was a short-term climatic anomaly with no equal in the meteorological records of that state. Any event of such magnitude would be expected to affect both phenology and reproductive success of a great variety of organisms, especially annual or ephemeral species. Since 1972 the phenology of entire butterfly faunas has been monitored along a transect paralleling Interstate Highway 80 from sea level at Suisun Bay to 2750 m at Castle Peak, north-central California. This has permitted year-toyear comparisons within localities as well as within-year comparisons among localities. This long-term study involving over 150 species includes the 1975-77 drought and the tremendous rains of winter 1977/78. Certain butterfly populations showed very pro-