Alternating Temperatures Enhance the Hatchability of Overwintered Eggs of the Gall-forming Aphid Paracolopha morrisoni (Aphidoidea : Eriosomatinae)(Physiology, Biochemistry, Development and Genetics)

Overwintered eggs of the gall-forming aphid Paracolopha morrisoni hatch early in spring synchronously with the budburst of the primary host plant Zelkova serrata. During embryogenesis the eggs are exposed to increasing mean temperature with diel fluctuations. This study examined the effects of temperatures and the odor of expanding host buds on egg hatching. Overwintered eggs were incubated in darkness at constant (14, 17, 20 and 24℃), increasing (from 14℃ to 24℃) and alternating (19 : 7℃ and 20 : 14℃) temperatures. Hatchability at the constant temperatures was low, ranging from 15% to 34%, with the maximum at 20℃. At this temperature, however, 98% of the eggs advanced embryogenesis until eyes became discernible. A stepwise temperature increase without diel fluctuations had no positive effect on hatchability. Incubation under the alternating temperature regimes increased hatchability to 78% and reduced the heat sum required for hatching. When eggs were incubated with and without cut unfolding buds of Z. serrata under the alternating 19 : 7℃ regime, the presence of host buds had no effect on the hatchability and hatching time of the eggs. These results indicate that embryogenesis can proceed under various temperature conditions without being influenced by host chemicals but that daily cycles of temperature are prerequisite for hatching.