Abstract: 【Aim】 To understand the action mechanisms of ultraviolet B (UV-B) radiation in successive generations on the change of protective enzyme activities in the grain aphid, Sitobion avenae (Fabricius) and to find the drive on insect evolution under the pressure of UV-B environment.【Methods】 In this study, we used 0.25 W/m² of UV-B to radiate each generation of S. avenae for 6 h, and then continuously reared the nymphs for 18 generations. We chose the 1st, 4th, 8th, 12th, 15th, 18th generations of wingless and parthenogenetic adults in both the treatment group and control group, and used spectrophotometry to measure the activities of three protective enzymes (superoxide dismutase, SOD; peroxidase, POD; catalase, CAT) in them. 【Results】 The activities of SOD, CAT and POD in the control groups of different generations had no significant difference (P>0.05), while those in the treatment groups of different generations had significant difference (P<0.05). With the increase of the generations under UV-B radiation , the SOD activity first rose and then declined, reaching the peak in the 15th generation. The POD activity showed a declining trend with the increase of the generations under UV-B radiation but kept higher than that in the control group, and only in the 1st and 4th generations were there significant differences in the POD activity between the treatment group and the control group. The CAT activity first fell and subsequently increased with the increase of the generations under UV-B radiation, and those in the 8th, 12th and 15th generations under UV-B radiation showed no significant difference with the control group (P<0.05), but the CAT activity in the 18th generation under UV-B radiation showed extremely significant difference with that of the control group (P<0.01). 【Conclusion】 When S. avenae is irradiated by UV-B for a short time, the activities of protective enzymes in the body rise to resist the damage of radicals. As UV-B radiation works longer, the POD activity tends to be stable, while the SOD and CAT activities are significantly higher than the normal level to protect against UV-B stress.  

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