Abstract. 1. The incidence of diapause in twenty‐three populations of Plodia interpunctella from fifteen countries representing all continents of the world was examined. The origins of populations varied from 52°N to 35°S and included two from equatorial regions. 2. Diapause occurred in all population samples at 20°C in short photoperiods (LD 11:13) and in continuous light, although the proportion of larvae doing so was less than 25% in samples from the equatorial belt. 3. The critical photoperiod was less than 13 h in five samples, all from the tropics, or southern hemisphere. The remaining samples, including three from the southern hemisphere, had critical photoperiods of 13 h or more. 4. Diapause was completely avoided by a 15 h photoperiod at 20°C in thirteen of the twenty‐three samples, including all but one of those from the southern hemisphere. 5. At 25°C larvae entered diapause in short photoperiods (LD 9:15) in about half of the samples tested in both hemispheres, but the proportion per sample was always less than a third. Copyright © 1979, Wiley Blackwell. All rights reserved
