Diapause in twenty-three populations of Plodia interpunctella (Hübner) (Lep., Pyralidae) from different parts of the world

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.