THERMAL REQUIREMENTS OF DIAERETIELLA-RAPAE (MINTOSH) ON RUSSIAN WHEAT APHID (DIURAPHIS-NOXIA MORDWILKO, HOM, APHIDIDAE) HOSTS
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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. eggmummy, mummyadult, eggadult) in Diaeretiella rapae (M'Intosh) (Hym., Aphidiidae) from China on Diuraphis noxia (Mordwilko) (Hom., Aphididae) hosts. Experiments were conducted at 5 constant temperatures: 10.0, 15.5, 21.1, 26.7, and 29.4C (1.0C). Photoperiod and humidity conditions were maintained at 14L: 10D and 5070% 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 eggmummy period increased from 7.3 days at 29.4C to 28.5 days at 10.0C; for the mummyadult period from 4.6 days at 29.4C to 20.0 days at 10.0C; and for the eggadult period from 11.3 days at 29.4C to 48.3 days at 10.0C. At all five temperatures, the developmental times for the eggmummy period were longer than the developmental times for the mummyadult period. There were no differences in developmental times between males and females at the temperatures tested except at 15.5C 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, 2.47C and 198.99 degreedays for the eggmummy period; 3.89C and 106.45 degreedays for the mummyadult period; and 3.56C and 292.29 degreedays for the eggadult period. The upper developmental threshold for the three developmental periods is considered to be above, but near 29.4C since the developmental rate decelerated but did not cease at this temperature. 1995 Blackwell Verlag GmbH
