Photoperiodic and temperature control of reproductive diapause induction in the predatory bug Orius strigicollis (Heteroptera: Anthocoridae) and its implications for biological control

The effect of day-length and temperature on the duration of the egg to adult period and reproductive diapause in Orius strigicollis (Poppius) (Heteroptera: Anthocoridae) from central Japan (36°N; 140°E) was studied in the laboratory. At 20 °C, the egg to adult period tended to increase with lengthening of photoperiod from short day [10:14 (L:D) h] to long day [14:10 (L:D) h], but slightly decreased with further lengthening of photoperiod, whereas at 24 °C, an opposite trend was recorded. At 28 °C, the developmental period was much shorter and there were no obvious trends. It is assumed that photoperiod-mediated acceleration of nymphal growth takes place in autumn when ambient temperature and natural day-length are decreasing, thus promoting earlier emergence of adults prior to the deterioration of environmental conditions. The species showed a long-day photoperiodic response of reproductive diapause induction: at 20 and 24 °C, 83–100% females entered diapause under short-day conditions [10:14 (L:D), 11:13 (L:D), and 12:12 (L:D) h], whereas 82–91% of females were reproductive under long-day conditions [14:10 (L:D), 15:9 (L:D), and 16:8 (L:D) h]. The critical day-length was close to 13 h at 20 °C and to 12.5 h at 24 °C. Diapause induction was strongly suppressed at 28 °C: its incidence did not exceed 50% even at 10:14 (L:D) h. It is estimated that O. strigicollis produces four or five generations in central Japan. The seasonal cycle and tendency to enter diapause are compared with other Orius species and other geographical populations of O. strigicollis. Implications of diapause-related traits for biological control are discussed.