Abstract
The critical photoperiod for short-day induced diapause was examined in eight different populations of Orius sauteri collected from northern Japan (36.0°N-45.4°N). Five out of six populations from Hokkaido had steep long-day type photoperiodic responses, i.e., almost all females grown under 14L-10D or shorter photoregime entered reproductive diapause and as little as a 1 h transition of photoperiod around the critical photoperiod drastically changed the diapause response. The curves of the photoperiodic response were relatively gentle in the most southern population of the Hokkaido and two northern Honshu populations. In particular, some females of the Tsukuba population (36.0°N) even laid eggs under such short daylengths as 11L-13D or 12L-12D. The critical photoperiod was longer in the populations from higher latitudes and shorter in those from lower latitudes, i.e., a clinal relationship was observed. The benefit of introduction of the southern populations to Hokkaido was discussed from the viewpoint of diapause. The advantages of the use of non-diapause strains selected from southern populations such as the Tsukuba population were also considered.
