Abstract
Effects of temperature and photoperiod on the development of Plusia agnata STAUDINGER, one of the major defoliators of soybean, were investigated in the laboratory. The number of moults in the larval stage varied from five to seven, and the appearance rate of the 6th instar type was higher than that of the others under the condition of 17-30°C. The threshold temperatures for the development in egg, larva, pupa and egg to adult emergence were 8.9, 7.9, 10.5 and 9.0°C and the thermal constants 56. 5, 263.2, 109.9 and 434.9 day-degrees, respectively. Neither larval nor pupal diapause was induced by a short photoperiod of 8L-16D. The factors affecting the number of instars, the number of generations a year and the possibility of overwintering in Fukuoka Prefecture were discussed.
