THERMAL REQUIREMENTS OF DIAERETIELLA-RAPAE (MINTOSH) ON RUSSIAN WHEAT APHID (DIURAPHIS-NOXIA MORDWILKO, HOM, APHIDIDAE) HOSTS

Studies were undertaken to assess the effect of temperature on development, and to estimate the thermal requirements (t and K) and upper developmental thresholds of three developmental periods (i.e. egg-mummy, mummy-adult, egg-adult) in Diaeretiella rapae (M'Intosh) (Hym., Aphidiidae) from China on Diuraphis noxia (Mordwilko) (Hem., Aphididae) hosts. Experiments were conducted at 5 constant temperatures: 10.0, 15.5, 21.1, 26.7, and 29.4 degrees C (+/-1.0 degrees C). Photoperiod and humidity conditions were maintained at 14L:10D and 50-70% R.H., respectively. In general, the developmental times and rates for the three developmental periods in D. rapae were influenced by the temperature to which they were exposed. Developmental times for the egg-mummy period increased from 7.3 days at 29.4 degrees C to 28.5 days at 10.0 degrees C; for the mummy-adult period from 4.6 days at 29.4 degrees C to 20.0 days at 10.0 degrees C; and for the egg-adult period from 11.3 days at 29.4 degrees C to 48.3 days at 10.0 degrees C. At all five temperatures, the developmental times for the egg-mummy period were longer than the developmental times for the mummy-adult period. There were no differences in developmental times between males and females at the temperatures tested except at 15.5 degrees C where males developed slightly faster than females (P < 0.011), i.e. 23.2 and 24.0 days, respectively. The estimated t and K values were, respectively, 2.47 degrees C and 198.99 degree-days for the egg-mummy period; 3.89 degrees C and 106.45 degree-days for the mummy-adult period; and 3.56 degrees C and 292.29 degree-days for the egg-adult period. The upper developmental threshold for the three developmental periods is considered to be above, but near 29.4 degrees C since the developmental rate decelerated but did not cease at this temperature.