1. Egg hatch in the two species of sycamore aphid was temporally separated: the median time to hatch was 30 days later in Drepanosiphum acerinum than in D.platanoidis. 2. D.platanoidis was larger at egg hatch than D.acerinum. Progeny of D.platanoidis adults were also larger than those of D.acerinum. 3. D.platanoidis was the larger of the two species as an adult, as a consequence of its greater birth weight. 4. Over a range of temperatures, development rates in the two species were the same, while the growth rate in D.acerinum was significantly higher at high temperatures. 5. The reproductive rate of the two species was significantly different at 6d̀C and 20d̀C.
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