On the direct influence of photoperiod on diapause in Trichogramma embryophagum (Hymenoptera,Trichogrammatidae)

A direct photoperiodic reaction of T. embryophagum larvae was investigated in the laboratory. Maternal females developed at 20°C and day length of 12 h. Progeny generation developed at 14°C and day lengths of 0, 4, 8, 12, 16, 20, and 24 h. Experiments showed that under the short days (12, 8, and 4 h) and in continuous darkness, the percentage of diapausing individuals was significantly higher than under the long days of 16 and 20 h. Under permanent light, however, the inclination to diapause also increased. The earlier investigated maternal influence on T. embryophagum progeny diapause showed a somewhat different pattern of photoperiodic reaction. These results suggest that the direct effect of the day length on Trichogramma diapause is a relatively autonomous process rather than just a side-effect of the photoperiodic reaction determining maternal influence. However, this direct effect is very weak and could possibly be a “rudimentary reaction.”