Diapause termination and thermal requirements for postdiapause development in Aphelinus mali at constant and fluctuating temperatures
1990
Trimble, R.M. | Blommers, L.H.M. | Helsen, H.H.M.
Diapause termination under natural and simulated overwintering conditions, the effect of subzero temperature on postdiapause development and the relationship between postdiapause development rate and constant and fluctuating temperatures was studied in a Dutch population of Aphelinus mali Hald. (Hymenoptera: Aphelinidae). The rate of diapause termination was similar in larvae overwintering under natural and simulated conditions. Most larvae had terminated diapause by the last week of February. Some female larvae may have remained in diapause until the end of March. The exposure of postdiapause larvae to −10 °C for two weeks did not affect their survival or postdiapause development rate. Postdiapause A. mali larvae could complete development and the adults emerge from their mummified aphid hosts at constant temperatures from 12 to 24 °C. Although some larvae completed postdiapause development at 10 °C, few emerged. The theoretical threshold temperature (to) for postdiapause development was 9.4 °C and the thermal constant (K) 136.4 degree-days. K was 121.4 and 134.8 for first and 50% emergence, respectively. The number of heat units accumulating above 9.4 °C to 1st and 50% emergence was similar under constant and fluctuating temperatures.
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