[Ecological and evolutionary aspects of photothermal regulation of diapause in Trichogramma]

Facultative winter diapause in species of the genus Trichogramma Westw. (Hymenoptera, Trichogrammatidae) is regulated, like in the majority of other insects, by photoperiod and temperature. In trichograms, prepupae are diapausing, but sensitivity to length of the light day and to temperature as to the cue factors inducing diapause is characteristic of all stages of development from embryo to the egg-laying female. The action of the cue factors affects not only the current, but also the subsequent generations. Under natural conditions the photothermal regulation provides the timely induction of the diapause coordinated both with astronomical year time (the photoperiodic reaction) and with specificity of this season (the temperature reaction). In the course of special experiments in trichograms there are also revealed the "rudimentary" reactions that have lost their adaptive role. Results of these studies prove once more that specificity of photoperiodic and temperature reactions inducing diapause and their relative importance and confinement to certain sensitive stages are determined not only by peculiarities of ecology of different insect taxa, but also by the course of their previous evolution.