Abstract
Laboratory investigations demonstrated that the survival of the preimaginal stages and pharate adults of Trichogramma principium was not significantly dependent on temperature over the range from 17 to 30°C but the temperature of 35°C caused a two-fold decrease in the mean number of survived progeny per one female. The rate of the preimaginal development of T. principium (from oviposition to adult emergence) at the temperatures of 17–30°C could be rather closely approximated by linear regression. The sum of effective temperatures was 145–150 degree-days with the lower threshold of about 11.8°C. In addition, at a temperature of 17°C the duration of development significantly (P < 0.001 with the Student’s t-test) depended on the day length: the mean and SD constituted 26.96 ± 0.34 and 27.85 ± 0.27 days at photoperiods of 12 and 18 h, correspondingly. The adaptive role of this quantitative photoperiodic response is not clear. Potentially, the “autumnal acceleration” of development, triggered by the combination of low temperature and short day, raises the proportion of individuals that have reached the diapausing stage before the winter season.
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