| With the increasing of human activities such as metallurgy, usage of polluted mud, treatment of debris and polluted water irrigation, more and more heavy metals permeate the earth environment. As the heavy metals cannot be degraded, they can accumulate in the body of animals and affect the biological level. Under the burden of excessive heavy metals, the insects can discharge part of them through feces or molting by utilizing all kinds of defense or detoxification in order to prevent from the damage imposed by excessive heavy metals.The herbivorous insect Oxya chinensis is a crucial agricultural pest that feeds on gramineous plants and is characterized by huge appetite and strong reproductive capacity. The thesis made a profound analysis on the accumulation of Zn and Cd in insect body and the effect of Zn and Cd on the antioxidant defense system of insect that could be generalized as follows:Under the condition of artificial stimulation ecological environment, the1st instar nymphs of Oxya chinensis was feed with Cd-Zn contaminated wheat seedlings for the chronic intoxication, then the Cd-Zn concentration of wheat seedlings, and slough and feces of Oxya chinensis was measured by atomic absorption spectrometry. The results showed that in the team with the same period of growth, the concentration of Cd increased and then decreased, and the concentration of Zn in the insect body depended on the concentration of Zn solution. In different growth periods of Oxya chinensis, the concentration showed a tendency of descending after ascending. The concentration level of imago was equivalent to the initial period of intoxication. The accumulation order of Cd and Zn in the feces was that the concentration of Cd in the feces of the2nd instar nymphs was the highest in the team with the same period of growth, the concentration of Cd in the feces increased and then stabilized, and the concentration of Zn in the feces of the2nd instar nymphs was also the highest while the lowest was in the feces of imago. In the team with the same period of growth, the concentration of Zn in the feces of Oxya chinensis increased in direct proportion to that in the wheat seedlings. The accumulation order of Cd and Zn in the slough was that the both concentrations drop obviously in the period of imago. The effect of dual contamination of Cd-Zn on SOD and GPx activity, T-Aoc and malonaldehyde was studied by means of spectrophotometry. The results showed that in all periods of growth, the concentration of MDA increased with the increasing of Zn and with the concentration of heavy metals in the insect body. The activity of SOD reached its maximum value at the4th and5th instar nymphs and the value of imago was a little lower than that of the5th instar nymphs. The GPx activity under the unique Cd treatment was higher than the contrast team while descended with the augment of the Zn concentration and reached its lowest value at Cd20mg·L-1+Zn200mg·L-1. The T-Aoc in the Cd-Zn treatment team was higher than the contrast team and reached its maximum value at Cd20mg·L-1+Zn100mg·L-1, and reached its lowest value at Cd20mg·L-1+Zn200mg·L-1. The5th instar nymphs and the imago was lower than the2nd to4th instar nymphs and there existed a huge difference(P<0.05).Then the change rules for MDA and antioxidant within different time periods under the condition of acute intoxication were analyze by injecting the Cd-Zn to the5th instar nymphs. The results showed that under the constant concentration of Cd, the MDA increased with the increasing of Zn and reached its maximum at Cd20mg·L-1+Zn200mg·L-1and there existed a huge difference (P<0.05). The activity of SOD presented a tendency of descending after ascending, the activity of enzyme droped tremendously at Cd20mg·L-1+Zn200mg·L-1and there existed a huge difference (P<0.05). The enzyme of GPx was lower than the contrast team after48h and72h of treatment. |
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