Abstract: The differentiation of sexual morphs of the pea aphid, Acyrthosiphon pisum (red morph) in the 3rd generation after 2 continuous generations under different photoperiods (8L∶16D, 10L∶14D, 12L∶12D and 14L∶10D) was observed in lab. The results showed that the ovipara of red pea aphid in Lanzhou were wingless, while males were winged. Photoperiod had a significant influence on the differentiation of sexual morphs of pea aphid (P<0.05). No sexual morph was produced under 14L∶10D photoperiod, but the sexual morphs were produced under the other photoperiods (8L∶16D, 10L∶14D and 12L∶12D). The percentage of male sexual morphs gradually diminished, while the percentage of ovipara remained unchanged in the 3rd generation with decreasing illumination time. The percentages of males and sexual morphs were the highest (15.03% and 91.43% respectively) under 12L∶12D photoperiod, but the percentage of vivipara was the lowest (8.57%). Under 10L∶14D photoperiod, the percentage of vivipara was the highest, but the percentage of sexual morphs was the lowest. Under 8L∶16D photoperiod, the percentage of ovipara was the highest (78.88%), but was not significantly different from those of the other treatments (P>0.05). The reproductive period of the 1st generation also had a significant influence on the differentiation of sexual morphs in the 3rd generation under the same short illumination conditions (P<0.05). Meanwhile, there was a certain time sequence to produce sexual morphs of pea aphid (first ovipara and last males) with some vivipara in the process of sexual morph transition. Hence, the critical photoperiod of red pea aphid was between 12 to 14 hours of illumination. Relatively longer illumination was advantageous to produce males, while the male differentiation time was delayed and the male differentiation days were shortened with decreasing illumination time. The results suggested that the photoperiodic change was a critical factor of reproductive plasticity and sexual morph differentiation of red pea aphid. The illumination length by which maternal pea aphid experienced influenced sexual differentiation of offspring.

Key words: Pinus koraiensis, diameter at breast height, tree-ring, latitude, climate change