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

Studies were undertaken to assess the effect of temperature on develop ment, and to estimate the thermal requirements (t and K) and upper dev elopmental thresholds of three developmental periods (i.e. egg-mummy, mummy-adult, egg-adult) in Diaeretiella rapae (M'Intosh) (Hym., Aphidi idae) from China on Diuraphis noxia (Mordwilko) (Hem., Aphididae) host s. 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 hum idity conditions were maintained at 14L:10D and 50-70% R.H., respectiv ely. In general, the developmental times and rates for the three devel opmental periods in D. rapae were influenced by the temperature to whi ch they were exposed. Developmental times for the egg-mummy period inc reased 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 da ys at 10.0 degrees C; and for the egg-adult period from 11.3 days at 2 9.4 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 th e developmental times for the mummy-adult period. There were no differ ences in developmental times between males and females at the temperat ures tested except at 15.5 degrees C where males developed slightly fa ster 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 19 8.99 degree-days for the egg-mummy period; 3.89 degrees C and 106.45 d egree-days for the mummy-adult period; and 3.56 degrees C and 292.29 d egree-days for the egg-adult period. The upper developmental threshold for the three developmental periods is considered to be above, but ne ar 29.4 degrees C since the developmental rate decelerated but did not cease at this temperature.