Effect of temperature on photoperiodic response in a selected 'non-diapause' strain of Pyrrhocoris apterus (Heteroptera)

The artificially selected 'non-diapause' strain of Pyrrhocoris apterus (L.) (Heteroptera) showed no diapause response to photoperiod at 26 degrees C (Socha & Hodkova, 1994). However, the diapause response to short-day photoperiod (LD 12:12 h) became apparent at lower temperatures of 17 degrees C (70% diapause) or 20 degrees C (41% diapause), Diapause was induced in 60% females by short-day photoperiod combined with thermoperiod of 26/16 degrees C, whereas only 20% diapause was induced by the same thermoperiod under continuous darkness. Thus the time-measuring system was not removed by artificial selection but the diapause response was shifted to lower temperatures, The diapause response to short days seems to be favoured rather by low temperature during scotophase than by low temperature throughout the whole light/dark cycle. If the percentage of diapause at 26 degrees C is compared in F-1 hybrids and in wild and selected parental strains the diapause appears to be dominant at LD 13:11 h but recessive at LD 11:13 h and LD 10:14 h, A hypothesis is proposed that the inheritance of the percentage of diapause in F1 hybrids is determined by interactions of genes controlling the temperature dependence of photoperiodic response.