THE "PHENOLOGICAL DATE" AS AN INDICATOR OF THE FLIGHT PERIOD OF NOCTUID MOTHS

Abstract

Climatic factors which may control the time of occurrence of seasonal phenomena are discussed, and in particular the role of temperature in initiating periodic cycles in animals in continental North America. The seasonal flight periods of nine species of noctuid moths at two localities in western North America are considered in terms of the lengths of the summer season at these localities. Among the species discussed, those that are in flight prior to midsummer fly earlier, and those that are in flight after midsummer fly later, in the area with a long summer than in the area with a short summer. A factor termed the "phenological date," which is based on the number of days above 42°F in a given area, is proposed as a measure of seasonal development. The factors of photoperiod and temperature that may have a controlling influence on periodic events are discussed. Variance analysis suggests that the phenological date has greater predictive value in estimating the periods of flight of the species considered than have the other factors.